Wood Protection for Log Home Owners

PB1767

$7.00

ContentsBasics of Wood 3 Wood Anatomy 3 Sapwood and Heartwood Wood Species Differences 4 Appearance Strength Wood and Water 5 Moisture Content of Wood and the Fiber Saturation Point Green Wood and Seasoning Hardwoods vs Softwoods Wood Shrinkage Kiln Drying Wood Deterioration 7 Physical and Mechanical Damage 7 Sunlight and Weathering Settling Checking Standing Dead Timber for Log Homes Fire Biological Damage 9 Insect Attack of Wood Fungal Attack of Wood Mold on Wood Non-microbial Stains Dry Rot Isn’t DryWood Protection for Log Homes 15 Importance of Keeping Wood Dry 15 Wood Preservatives 16 Sapstain Chemicals Restricted-use Preservatives Boron-based Preservatives Natural Durability Finishes 18 The Weathered Look — A Traditional Finish for Log Homes Application of Finishes & Refinishing The Durability Pyramid 19 Dry Design Careful Construction Durable Materials Inspection and MaintenanceReferences 22

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Wood Protection for Log Home OwnersAdam M. Taylor Assistant ProfessorTennessee Forest Products CenterUniversity of Tennessee

Stephen L. QuarlesWood Durability AdvisorUniversity of California Cooperative Extension

Karen M. VailAssociate ProfessorEntomology and Plant PathologyUniversity of Tennessee

Woodisabeautifulmaterialthathasbeenusedforcenturiesforbuildingloghomes.Woodisalsoahighperformancecompositewithgoodstrength,insulation,fireresistanceanddurabilitycharacter-istics.Thismeansthatuniquelybeautifulloghomescanbeasefficientandlong-lastingasstructuresmadefromwoodenlumber,steelorconcrete.

Anunderstandingofwoodpropertieswillhelploghomeownersprotectandenjoytheirhomes.Thispublicationisdesignedtoprovidebasicinfor-mationaboutwood,woodprotectionandtheuseoflargetimberstobuildloghomes.

Basics of WoodTheroleofwoodintreesistoprovidestructural

supportandtoconductwaterupfromthegroundtotheleaves.Thus,woodneedstobestrongbutalsoporous.Woodinlivingtreescontainsalotofwaterand,althoughwooddriesandshrinksafterharvest,

thelogsinahomealwayscontainsomeamountofwater.Therelationshipofwaterandwoodisthemostimportantfactorindeterminingthebehaviorofwoodandhowlongitwilllast.Inaddition,lum-berandotherwood-basedproductscomefromawiderangeoftreespeciesthathavedifferentprop-erties.Treesalsochangeastheygrowolder,sowoodishighlyvariable.Finally,wood—anorganicma-terial—isbiodegradableandcanbebrokendowninmanywaysintothecarbondioxideandenergy(trappedsunlight)fromwhichitwasmade.

Wood AnatomyWoodismadeofthousandsofsmallcells,

whicharelong,slendertubes.Mostofthecellsareorientedparalleltothelengthofthetreetrunk,andthisgiveswoodagraininthatdirection.Ifyoucutacrossthetreestem,youexposetheopenendsofthousandsofcells.Thisendgrainabsorbs(orreleases)watermuchmorequicklythantheotherwoodsurfaces,whichcanhaveimportantimplica-tionsfortryingtokeepwooddryandprotectedfromdecayandinsects.

Sapwood and heartwoodSapwoodistheouterbandofwoodthatcontains

somelivingcellsandalsoconductswaterinthelivingtree.Theinnercoreofheartwoodcontainsonlydeadcells.Theheartwoodofsomenaturallydurabletreespeciescontainschemicals(extractives)

Log homes can be beautiful and long-lasting. The most important factor in making your log home a durable structure is a design that keeps the wood dry.

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thatrepelfungaldecay(rot)andinsects.Examplesofnaturallydurablewoodsthatareusedinloghomesincludecedars,cypressandwhiteoak.Extractivescanalsoresultinspecialcolorsorodorsinthewood.Forexample,incensecedarheartwoodgivespencilstheircharacteristicodorandtheheartwoodofebony(usedfortheblackkeysonapiano)isblack.Thesapwoodofallspeciesislightincolorandissusceptibletodecayandinsectattack.

Wood Species DifferencesManydifferenttreesareusedformakinglog

homes,includingvariouspines,oak,cypress,cedarandothers.Logsfromthesetreesvaryinappear-ance,strength,weight,howeasilytheydry,andtheirnaturalresistancetodecayandinsects.Loghomebuilderscantakeadvantageofthenaturalfeaturesofsomespecies,butgivenproperdesign,anyspeciescanbeusedtomakeanattractiveanddurablestructure.

AppearanceWoodvariesincolor,grain,knotpattern,ten-

dencytosplitorstain,andotherfeaturesthatcan

affectthelookofalog.Themostattractivewoodspeciesisamatterofpersonalchoice.Theouterwoodclosesttothebark(sapwood)ofalltreestemshasalightcolor,soifroundlogsareused,thecolorofthefreshlogwillbelight.Theinnerwood(heart-wood)canbeexposedwhenlogsarecut,forexam-ple,insquaredtimbers.Inspeciessuchascedarandredwood,theheartwoodhasadarkcolor.Thecolor(andodor,insomecases)ofthesespeciesisprizedbysomepeople.Ofcourse,thecoloroflogscanalsobechangedbyusingfinishes;awidevarietyofstainsisavailableforthispurpose.

StrengthWoodisremarkablystrong.Dependingonhow

strengthismeasured,woodcanbestrongerperunitweightthansteel.Differentwoodspecieshavedifferentstrengthratings;and,ingeneral,heavierwoods(hardhardwoodssuchasoak)arestrongerthanlessdensewoodssuchaspineorcedar.How-ever,woodissufficientlystrongthatthestrengthofthewoodspeciesisnotanimportantconsider-ationforlogwalls.Ingeneral,allspecieswillbestrongenoughgivenproperdesign.

Bark

Longitudinal direction — almost no shrinkage

One growth ring of wood is formed each year.

Anatomyof a log

Sapwood — light colored wood

Heartwood — may be naturally durable

Tangential direction — shrinks twice as much as the radial direction

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Hardwoods vs. SoftwoodsPeople often refer to some species

of trees as soft hardwoods or hard hard-woods. To make matters more confusing, pines can be grouped as hard pines or soft pines, even though all pines are softwoods. So how can wood be hard and soft at the same time?

The classification of tree species as hardwoods or softwoods is based on a bo-tanical distinction. Softwoods (or gymno-sperms) are the conifers, or cone-bearing trees, that are often evergreen and have needle-like leaves. Softwoods include the pines, eastern redcedar and cypress. Hard-woods (or angiosperms) are broad-leaved, mostly deciduous trees, that is, they drop their leaves. Oaks and poplar are examples of hardwoods.

The wood of both hardwoods and soft-woods varies in hardness, and this is the source of confusion: hard and soft wood oc-curs in different species of both hardwood and softwood trees. Hardness is a function of the heaviness, or density, of the wood: the amount of wood material compared to air spaces. Hard woods are denser, soft woods contain more air. On average, the wood of softwoods is softer than hardwoods. Howev-er, there are many exceptions to this trend. The Southern pines are softwoods, but they are denser than yellow poplar, which is a hardwood. Because of the wide range of wood density in the hardwood tree species, people will often distinguish between hard hardwoods (e.g. hickory, oak, ash) and soft hardwoods (e.g. yellow poplar, gum, willow). Likewise the pines, which are softwoods, can be organized into hard (e.g. Southern, red) and soft (white, sugar) groupings.

Both hardwoods and softwoods are used to make log homes. Factors such as size, cost, natural durability and appearance are generally more important considerations than whether the wood is relatively harder or softer, or a hardwood or a softwood.

Wood and WaterMoisture content of wood and the fiber saturation point

Forwoodproducts,theamountofwaterinwoodiscalledthemoisturecontent(MC)andismeasuredastheweightofwaterrelativetotheweightofbone-drywood.Accordingtothismethodofmeasur-ing,unseasoned(green)woodcanhaveamoisturecontentover100percent!Fullyseasonedwoodwillhaveamoisturecontentrangingfrom5percentto15percent,dependingonthetemperatureandrela-tivehumidityofitsenvironment.

Waterexistsintwoformsinwood.Liquid,orfree,waterfillsthehollowcentersofwoodcellsandothervoidregions.Boundwaterischemicallylinkedtothecellwall.Asgreenwoodbeginstodry,freewaterisremoved.Afterallofthefreewaterhasgonebutalloftheboundwaterremains,thewoodisattheso-calledfiber saturation point(FSP).Thisoccursatabout25percentmoisturecontent.Furtherdryingbelowthefibersaturationpointismoredif-ficult(requiresmoreenergy)becausetheboundwa-terhasastrongattractiontothewood.Itshouldbenotedthatduringdrying,moistureisnotevenlydis-tributedthroughoutthewood.ThusthesurfaceofadryinglogmightbebelowtheFSPatthesametimethattheinnerportionsofthelogarestillverywet.

Thefibersaturationpointhasimportantimplica-tionsforwoodproperties.Belowthefibersaturationpoint,fungalgrowth(moldordecay)cannotoccurandwoodislessattractivetomanyinsects.IfwoodcanbedriedrapidlyandmaintainedatamoisturecontentbelowtheFSP,itwillbeverydurable.Fortunately,ifwoodiskeptoutofcontactwithliquidwater,itwilleventuallydrytoamoisturecontentbelowtheFSP.

Green wood and seasoningWhenalivingtreeiscut,thewoodisgreen—it

containsalotofwater.Insomespecies,therecanbemorewaterby(measuredbyweight)inthewoodthanthereisdrywood.Themoisturecontentofthewoodexceeds100percentinthesesituations.Afterthewoodiscut,mostofthiswater(butnotall)willevaporatefromthewood.Eventuallytheamountofwaterinthewoodwillcometoabalancewiththeamountofwaterintheair.Atthatpointthewoodisdryorseasoned.Theamountoftimethatittakes

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forwoodtogofromgreentoseasoneddependsonmanyfactors,includingthetemperatureandrelativehumidityoftheair,andthesizeandspeciesofthepieceofwood.Inthecaseoflogs,thisprocesscantakeafewyears.Iflogsarekiln-driedpriortoassembly,thetimetoreachmoistureequilibriumwillbereduced.

Ifthelogsinaloghomearewettedduetorainorotherwatersources,themoisturecontentofatleastthesurfaceregioncaneventuallybecomeveryhigh.Oncethewatersourceisremoved,thewoodwillagaindrytoanMCthatisinbalancewiththetemperatureandrelativehumidityoftheairsurroundingit.Thiseventualbalanceofmoistureinwoodwithconditionsinitsenvironmentiscalledtheequilibrium moisture content(EMC).

Wood shrinkageShrinkageoccurswhenwoodisdriedbelowthe

fibersaturationpoint.AbovetheFSP,theremovaloffreewatersimplyemptiesthewoodcellsanddoesnotchangetheirdimensions.Whenboundwaterisremovedfromthewallsofcells,theybegintoshrink.Asaruleofthumb,forevery3percentreductioninmoisturecontentbelowtheFSP,thewoodwillshrinkinvolumebyabout1percent.

Asmentionedabove,fullyseasonedwoodhasamoisturecontentrangingfrom5–15percent,dependingonitsenvironment,whilegreenwoodhasamoisturecontentwellabove25percent(abovetheFSP).Thusshrinkageisinevitablewhenwoodisusedforhouses.Evenmoreimportantly,woodshrinkageisnotuniform.Woodshrinksverylittleinlengthbutsubstantiallyacrossthegrain(5–10percentfromthegreensize).Thismeansthatthewallsofastick builthousewillchangeverylittleinheightasthewoodenstudsinthewallcavitiesdryout.Incontrast,awallmadefromlogscanshrinkseveralinchesinheight(thewidth-wisedirectioninthelog)asthewooddries.

Itisalsoimportanttoknowthatwoodshrinksabouttwiceasmuchparalleltothegrowthrings(tangentialdirection)asitdoesperpendiculartothegrowthrings(radialdirection).Thisimbalanceisthereasonwhysomesplittingofthesurfaceoflogsisinevitable(seechecking,below).

Kiln dryingKilndryingreferstoputtingwoodintoaheated

enclosure(akiln)toacceleratethedryingprocess.Kilndryingcanreducethedryingtimesforsomelumberspeciesfrommonthstodaysandcanalsore-ducedryingtimeforlogsandotherlargemembers.

WOOD & WATERNORMALIN-SERVICE

RANGE(5-15%)

NO FUNGAL GROWTHBELOW FSP

“GREEN”WOOD

(60-150%)

Shrinkage starts when wooddries below 25% M.C.

ONLY “ BOUND” WATER “FREE” WATER PRESENT

~25% MOISTURE CONTENT0%

~8%

SHRINKAGE

0%

Water has a large impact on wood properties. Trees are wet, but the logs in a house are relatively dry. Drying results in shrinkage, but it also helps protect the wood from attack by insects and fungi.

Resin is bleeding from this pine log. Kiln drying of the logs can prevent this.

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Anextremeexampleisthehigh-temperaturedry-ingofpinelumber,whichcanreducethemoisturecontentfromgreen(>100percent)to19percentinacoupleofdays.Inadditiontotherapidremovalofwater,theheatinadrykilncankillinsectsandotherorganismsthatmightbelivinginthewood,particularlythosethatmaybeinthestandingtrees,andwillalsohelptoset the pitch.Inresinousspe-ciessuchaspinessticky,defensiveliquids(pitch),producedbythetreeasadefenseagainstinsects,canleakoutofthewoodafteritiscut.Exposingthewoodtohightemperatureswillhardenthepitchsothatitwillnolongerbeanaestheticproblem.

Removingwaterfromwoodtolowerthemois-turecontentbelow25percentwillpreventattackbymoldanddecayfungi(rot).Kilndryingcanshortenthetimerequiredforalogtogettothissafercondition.Hardwoodlumberiskilndriedtoachieveamoisturecontent(5–15percent)thatwillpreventmostfutureshrinkage(assumingthelumberstaysinaninteriorenvironmentandisn’trewetted).Becauselogsarenotkilndriedtosuchlowlevels,shrinkageoflogswillcontinueafteraloghouseisassembled.

Wood DeteriorationWoodcanbedegraded

bybothphysicalfactorsandlivingorganisms.Woodisanorganized,solidcombinationofcarbondioxide,waterandenergyfromsunlight.Thevariousagentsthatbreakwooddownarepartofthenaturalrecyclingofwoodthatultimatelyendsinthe

releaseofcarbondioxide,waterandenergy.Withappropriatedesignandmaintenance,deteriorationcanbedelayedalmostindefinitely;thus,aloghomecanlastvirtuallyforever.

Physical and Mechanical DamageSunlight and weathering

Justasultravioletrays(UV)insunlightcancausechemicalchangesinourbodybytanningourskinorbleachingourhair,theycanalsocausechemicalchangesinwood.UVbreaksapartcom-poundsonthesurfaceofexposedwoodresultingindegradedwoodfibersandchangesincolor.WhenUVexposureiscombinedwithwindandwaterexposure,thiscanresultintheslowerosionofwoodfibersfromthesurfaceofthewood.Thisprocessiscalledweathering.Weatheringisusu-allyunevenanddependsonhowmuchsunlightandwaterthewoodisexposedtoandhowsoftthewoodis.Softwoodssuchascedarwillweatherfasterthanharderwoodssuchasoak.Also,thedifferentpartsoftheannualgrowthringsinapieceofwoodwillweatherunevenlybecausetheearlywood(woodformedinthespring)issofterthanthelatewood(formedinthesummer).This

This building has weathered siding. The darker areas are exposed to more sunlight. In protected areas under the eaves, the wood is closer to its original light color. Finishes can be used to prevent weathering and improve the appearance of exterior wood.

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resultsinroughsurfacesonweatheredwood—especiallyontheendgrain.

Theeffectsofweatheringarelimitedtothesur-faceofwood,andtheprocessisquiteslowoverall.Researchsuggeststhatwoodremovalduetoweath-eringisonlyabout½inchpercentury,evenwithsoftwoods.Thusweatheringisnotastructuralcon-cernforloghomeswithwallsthataremanyinchesthick.Thebiggerconcernwithweatheringisthechangedandirregular(non-uniform)colorofunpro-tectedwood,whichisanaestheticissue.

Weatheringcanbepreventedbyprotectingthewoodfromexposuretosunlightandwaterandbyapplyingfinishesthatblockultravioletradiationandshedliquidwater.Clearfinishescancontainchemi-calsthatareUVblockers.Pigmented(colored)fin-ishesalsoprotectwoodagainstUVexposure.

SettlingAsexplainedabove,woodshrinkswhenit

dries.Loghomesalwayscontinuetodryaftertheyareassembled,sosomeshrinkageoflogwallsisinevitable.Becauseshrinkageisgreatestacrossthegrain,logwallshrinkage—orsettling—canresultinaconsiderablechangeinwallheight.Forexample,a10footlogwallmaysettle2inchesormore,dependingonthewoodspeciesandthemois-turecontentofthelogswhentheywereassembled.Becauselumberisorientedinthelongitudinal(lowshrinkage)orientation,othercomponentsinaloghome—interiorstudwalls,windowsanddoors,andcabinets—donotsettleappreciably.Allow-ancesforsettlingmustbemadewhereverlogwallsconnecttotheseitems.

CheckingCheckingisthedevelopmentofcracksinthe

surfaceofwood.Woodshrinksmoreparalleltothegrowthringsthanitdoesacrossthegrowthrings.Thisimbalanceresultsinlargestressesaslogsdry.Inlogs,thesestresseseventuallyovercomethestrengthofthewood,whichfails,resultinginthedevelopmentofacheck.Thesechecksappearonthesurfaceaswidecracksthatextendinwardtowardthecenterofthelog.Thesechecksareduetonatu-ralwoodcharacteristicscombinedwithinevitabledrying.Becauseshrinkageparalleltothegrowthrings(thetangentialdirection)isapproximately

A check in a house log. This kind of split is the inevitable result of the normal drying process and the uneven nature of shrinkage in wood.

Standing Dead Timber for Log Homes

In some areas of the country, thousands of trees have been killed by insect or disease outbreaks. This standing dead timber can be used for log homes. Such logs may have a lower moisture content than normal green wood, which results in lighter logs and potentially a shorter seasoning time. However, even standing dead timber will continue to shrink and check after it is assembled into a log home. Furthermore, standing timber can be attacked by decay fungi or insects before it is harvested. Logs should always be inspected before use, but inspection is particularly important when the use of fallen, or standing dead trees is being considered.

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twicethatinthedirectionperpen-diculartothegrowthrings(theradialdirection),checksareimpossibletopre-ventandshouldbeconsideredanormalpartoftheloghomelook.Logsusuallydeveloponelargecheckinsteadofsev-eralsmallerones.Ifyoucanseewherethecheckisstarting,itissometimespossibletorotatethelogduringinstal-lationtohidethecheckorpositionitinalessvulnerablelocation.

Checkingcanalsooccurinwoodbecauseofrapiddrying.Whenthesurfaceofwooddries,itstartstoshrinkbeforetheinsideofthepiecedoes,causingstressestodevelopinthesurfacelayers.Ifthesedevelop-ingstressesexceedthestrengthofthewood,acheckdevelops.Thesechecksdonotnecessarilyextendacrossthegrowthringsandcanbepreventedbycarefuldrying.

FireWoodisacombustiblematerial.Thisisagood

thingwhenthefireisconfinedtoafireplaceorwoodstove,butitalsomeansthatloghousescanburn.However,thedangersoffirearenotusuallygreaterinloghomesthaninstructuresframedwithothermaterials.Firescanoccurinalmostanybuild-ingwhenkitchenaccidentsorelectricalproblemsigniteinteriorfurnishings.Thepotentialcombusti-bilityoflogwallsisnotreallyanadditionaldangerbecausesuchlargepiecesofwoodactuallyburnquiteslowlyduetothechar layerthatdevelops.Therefore,logsretainmostoftheirstrengthduringtheinitialstagesofafire.Becauseoftheprotectiveeffectofthecharlayer,buildingcodesusuallyas-signbetterfireratingstolargermembers.

Inwildland/urbaninterfaceareaswherewild-firesareaconcern,logwallscanbeapositivecomponentofamorefire-safehome.Themostvulnerablepartofthelogwallinaloghomeisthebetween log joint.Thejointshouldbefilledtopro-videprotectioncomparabletothelogitself.

Inawildfire,manyhomesarelostasaresultofflameoremberentryintoatticorcathedralceilingspaces.Toavoidtheseexposures,highlycombustible

vegetationshouldberemovedfromnearthelogwalls.Similarly,otheritemsthatcouldresultinigni-tionofthelogwall(e.g.,gasolinecontainers),withsubsequentflamespreadtotheeavearea,shouldalsobeavoided.

Biological DamageInsect attack of wood

Manykindsofinsectscanattackwood.Woodprovidessomeinsectswithsuitablehabitat(aplacetolive),foratleastpartoftheirlifecycle.Examplesoftheseinsectsincludecarpenterants,carpenterbeesandsomewood-boringbeetles.Otherinsectsattackwoodbecauseitprovidesafoodsource.Examplesofinsectsthateatwood(orpartsofwood)includetermitesandwood-boringbeetles.

TermitesTermitesarethemostseriousinsectpestof

loghomes.Termiteseatwoodandthuscancausemajorstructuraldamage.Termiteseitherliveinthewoodtheyareeating(drywoodordampwoodtermites)orinthesoilinthevicinityofthehousetheyareinfesting(subterraneantermites).Becausesubterraneantermitecoloniesarelargerthan

Dry wood has good insulating and fire-resistance properties. However, the gaps between logs are important in determining the overall performance of the wall. If the chinking that fills the gaps is missing, is in poor repair or has low fire-resistance properties, the wall may leak or perform poorly in a fire.

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drywoodtermitecolonies,theyarecapableofdoingmoredamagetoawoodstructure.FormosantermitesareoneverydestructivespeciesofsubterraneantermitefoundinthesoutheasternUnitesStates.Formosantermitescanbefoundinthesoil,butalsoinabovegroundlocationsincarton nests thatmaintainamoistenvironment.Cartonnestsaren’tinwoodmembersbutcanbeinwallcavitiesandhollowedouttrees.Becausedampwoodtermitesrequirewetwood,theyaren’tusuallyfoundinside.

Fortunately,anumberofeffectivetermitepesticidesandtreatmentsareavailablefrompestcontrolmanagementprofessionals.Knowingwherethetermiteslivecanhelpyouunderstandthebesttreatmentforagiveninfestation.Soiltreatments(baitsandliquidsoilapplications)canbeeffectiveagainstsubterraneantermites,includingtheFormosan,butwon’tbeeffectiveagainstdrywoodtermites.Similarly,wholehousefumigationorlocalchemicaltreatmentsinjectedintowoodmemberswillonlybeeffectiveagainsttermitesresidinginthetreatedmember.Thesetreatmentsarenoteffectiveagainstsubterraneantermites,whereonlyasmallfractionofthecolonyisinthehomeatanygiventime.Thebesttreatmentfordampwoodtermitesistodryouttheaffectedwoodmembers.

Apreconstructiontermitetreatmentisrecommendedfornewhomes.Homeownerscanalsotakestepstodiscouragetermiteinfestationsintheirhomes.Keepingpotentialtermitefood,suchasmulchandfirewood,awayfromlogwallscanhelptopreventtermiteinfestation.Termitesarealso

attractedtomoistureorpartially-rottenwood,sokeepingaloghomeandnearbyareasdrywillhelptoreducetheriskoftermiteattackinadditiontoreducingtheriskoffungaldecayormold.

Thefollowingareafewpracticalwaystopreventatermiteinfestation:• Repairstructuralandplumbingleaks.• Clearpilesofwoodandtrash.• Keepfirewoodpilesawayfromthestructure.• Keepguttersclean.Ensurethatwhendownspouts

terminateattheground,waterisdirectedawayfromthefoundation.

• Gradearoundthefoundationtodrawwaterawayfromthebuilding.

• Usepreservative-treatedlumberwhenwoodisingroundcontactandforthestructuralsupportmembersforexposedporchesanddecks.

Wood-Boring BeetlesCertainbeetleswillattackwood.Theycanbe

groupedintothosethatstaynearthebarklayer(barkbeetles)andthosethatboreintotheinternalstruc-tureofthewood(wood-boringbeetles).Theseinsectsboreintowoodtolaytheireggsandfeedoncarbo-hydrates(sugarsandstarch).Signsofabeetleinfes-tationincludesmallholesinthesurfaceofthewoodandnearbypilesofsawdustmixedwithwaste(fra-ss).Somespeciescanre-infestseasonedwood(logsinthiscase)whileothersthatinfestalivingtreewillnotreturnoncetheyhavelefttheseasonedwoodinaloghome.Theseinsectsalsovaryintheamountofdamagetheycause.Forthesereasons,itisimportant

Drywood termite damage in a fence. Drywood termites inhabit the wood they are eating.

The surface of this log has numerous powderpost beetle entry holes. Powderpost beetles can attack and re-infest logs after they are assembled into a home.

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toidentifytheinsectsothatthepropercontrolmea-surescanbetaken.1Insomecases,“control”willinvolveonlywaitingfortheinsectstofinishemerg-ingfromthelogsbecausetheywillnotreturn.

Reinfesting beetles. Powderpostbeetlesincludelyctid,anobiidandbostrichidbeetles.Theycanbedistinguishedbythetypeofwoodtheyattack,thesizeandshapeoftheboreandemergenceholesandthefrass.Powderpostbeetlescanreinfestdrywoodandcaneventuallycausesignificantdamage;how-ever,thisisaslowprocess.Somepowderpostbeetlespreferunfinishedwoodwithrelativelyhighmoisturecontent,sokeepingthewooddryandapplyingafinishlayermaybeenoughtokeeptheinsectfromreturningtothewood.Borate-basedwoodpreserva-tivesorinsecticidesrequireunseasoned(wet)woodtopenetrateandkillthebeetles.Spray-orbrush-appliedtreatments(tologsalreadyinahome)willnotpenetrateverydeeply.Therefore,inordertobetrulyeffectiveagainstexistingpowderpostbeetleinfestations,borate-basedpreservativesmustbeapplied,priortoassembly,usingapressureimpreg-nationprocess.Otherdip,brushorspraychemicaltreatmentsdonotpenetratethewood,buttheywillprovidelocalizedprotectionandmaypreventreinfestation.Certainlonghornedbeetles(Ceramby-cidae),suchastheoldhouseborer,canalsore-infestlogsinahome.Theseinsectspreferthesapwoodofsoftwoodssuchaspine.Largeoldhouseborerlarvaecanbeheardastheyfeed.Astethoscopeorotherlisteningdevicecanbeusedtolocatetheselarvae.Woodnearthegallerycanbedrilledandinjectedwithinsecticide.Despitetheirname,oldhouseborersareusuallyfoundinhomeslessthan10yearsold.

Non-reinfesting beetles.Ambrosiabeetles,barkbeetles,andmostflat-headedandround-headedbor-ersareinsectsthatwillnotre-infestlogsinahome.Exceptforthebarkbeetles,theseareboringbeetlesthatpenetrateintothewood.Althoughtheappear-anceoftheseinsectsmaybeunsightlyandalarming,theyarenotasignificantthreat.Oncetheycomeout

1If beetle attack is observed, the type of beetle should be determined. Contact an Extension entomologist for help with identification. More information on managing wood-infesting insects can be found in UT Extension’s PB1703 Wood Destroy-ing Organisms at http://eppserver.ag.utk.edu/PSEP/second-level/thirdlevel/WDO/WDOindex.htm. Extension personnel in many states have prepared Web-based information on wood-infesting organisms.

ofthelog,theyaregoneforgood.However,someoftheseinsectscantakemanyyearstodevelopandemerge,soitisimportanttohavethecorrectidentifi-cationbeforeconsideringcontrolmeasures.

Carpenter BeesCarpenterbeesarelargeflyinginsectsthatresemblebumblebees.Theydonoteatwood;rather,theyborelarge(½”diameter)holesintologsandotherexteriorwoodsurfacestoexcavategalleriesinwhichtolaytheireggs.Carpenterbeesarenotaggressiveandrarelysting.Althoughcarpenterbeescreatebigholesinwoodasbroodchambersfortheiryoung,theyareunlikelytocausestructuraldamage

This log shows attack by bark beetles that occurred when the tree was standing. This log is still structurally sound and the beetles will not cause further damage.

A carpenter bee hole in a rafter. Carpenter bees are a common pest of log homes.

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initially;however,repeateduseofthesamegalleriesovermanyyearsmaycausesignificantdamage.Itisbelievedthatcarpenterbeesarelesslikelytoboreintowoodthathasbeenpainted,butthefinishesgenerallyusedonloghomesdonotpreventattack.Moreresearchisneededtoevaluatepreventivecarpenterbeecontrolstrategies.Carpenterbees’galleries(holes)canbetreatedwithdust,sprayorfoaminsecticidesand,aftera24-hourwaitingperiod,physicallyblockedwithawooddoweltodiscouragefurtheractivity.Carpenterbeesarealsoveryslow-movingandwilloftenhoveraroundtheirholes.Forthisreason,manypeoplerecommendaflyswatterortennisracketasthemosteffectivemeansofcontrol.

Carpenter AntsCarpenterantsarelarge,oftenblack,antsthat

cannestinwood.Theyoftenpreferwetorpartiallyrottenwood.Unliketermites,carpenterantsdonoteatthewoodandarelesslikelytocausesignificantstructuraldamage.Signsofacarpenterantinfesta-tionincludeflyingants(alates)inoraroundthehomeandpilesofsawdustcontaininginsectpartsbelowantentrypoints.Carpenterantscanbeanui-sanceandcanbecontrolledbylocatingandtreatingthenestwithspray,dustorfoaminsecticides;baitingforagingants;ortreatingtrailsandpotentialentrypointswithanonrepellent,professionally-appliedinsecticide.Cleaningupkitchenwasteandotherpo-tentialfoodandeliminatingwatersourceswillhelpdiscourageantinfestations.Trimmingvegetationsothatitdoesnottouchthestructureandsealingwireandpipewallpenetrationscanalsoreduceantentryintothehome

Fungal attack of woodThefungi,whichincludethecommonbutton

mushroom,areorganismsthatdecomposeorganicmatter.Theyarenature’srecyclersandmanyspeciesoffungihavetheabilitytoattackwoodinvariousways.Thefungithatcanattackwoodaredividedintomold,stainanddecay(rot)groupsbasedonthedamagethattheycause.Decayfungiarethemostseriousthreat;however,thepresenceofanyactivefungusmeansthatthewoodiswetandatrisk.Keepingwooddrywillpreventfungalproblems.

Mold and Mildew FungiMoldcanbeseenasafuzzyordiscoloredlayer

onthesurfaceofwood.Moldsarefungithatgrowoncertainportionsofwood,bread,oranges,oranysurfacethatprovidesasuitablecombinationofmod-eratetemperature,moistureandfood.Mildewisan-othertermformold.Moldsfeedonnutrientsfoundinthestoragecellsinwoodandarepredominantlyonthesurfaceofwood.Theydonoteatorweakenthewooditself.

Mold on WoodRecently there has been increased

concern about mold on wood. Reports of so-called toxic molds, in particular, have caused people to be more interested in preventing, detecting and eliminating mold on the wood and other materials in their homes.

Under some conditions these molds can produce mycotoxins — special chemi-cals that can be toxic. Despite the alarm-ing name, the dangers of toxic molds are often over-emphasized. The musty smell of mold is not caused by mycotoxins. Most molds don’t produce mycotoxins, and even those molds that can produce mycotoxins don’t produce them all the time. In gen-eral, while moldy wood may be unsightly or trigger allergic reactions in sensitive in-dividuals. Typical exposures don’t pose a health hazard for most people.

Both termites (top) and ants (bottom) have flying reproductive forms (alates). Termites have straight antennae, equal length wings and abdomens that are as wide as the rest of their bodies. Ants have bent antennae, wings of unequal length and constricted waists.

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Molds(andotherfungi)producemillionsofmi-croscopicspores.Thesporesfrommostspeciesofmoldaredisseminatedbythemovementofair.Thesporesofsomespeciesattachthemselvestothebod-iesofinsects(usuallybeetles)andaredepositedwhentheinsectlands.Howevertheyarrive,oncethesesporeslandonthesurfaceofwood(orothermaterials)whenconditionsareright,anewgrowthofmoldwillresult.Air-bornemoldsporesareallaroundusandintheairwebreathe.Highconcentra-tionsofmoldsporesmaycauseallergicreactionsinsensitiveindividuals.

Thebestwaytopreventorstopmoldfromgrow-ingonwoodandwood-basedproductsistokeepthesurfacedry.Thismeansthatbathrooms,kitchensandbasementsshouldbewellventilated.Existingmoldcanberemovedbywashingwithwater,andbleachordetergentscanbeusedtoeliminatediscolorations.Unfortunately,iftheconditionsconduciveformoldgrowthremain,newsporeswilllandonthewoodandfreshmoldwillgrow.

Chemicaltreatmentsthatcanhelppreventmoldgrowthdoexist.However,thewarm,wetconditionsthatleadtomoldmayalsoleadtowoodrot,sopre-ventingtheelevatedmoisturecontentnecessaryformoldgrowthisthebestsolution.

Stain FungiUnlikemostmolds,stainfungicanpenetrate

belowthesurfacebyfollowingnaturallyoccurringvoidspacesandopeningsinthewoodcells(rays)thatextendfrombelowthebarktothecenterofthetree(pith).Becauseoftheirpigmentedhyphae,stainfungicauseblue,blackorbrowndiscolorationininfestedwood.Thesefungidonotsubstantiallyweakenthewood.Stainfungi—alsoknownasbluestainorsapstain—arerestrictedtosapwood,whichcontainsthesugarsandstarchesthatarefoodforthefungi.Sporesofstainfungicanquicklyattackfreshlyfallenlogs.Rapiddryingofthesurfaceofthewood(topreventsporegermination)orsurfaceapplicationoffungicidescanpreventstainfungifrombecomingestablished.Oncelogshavebeenseasoned,rewettingwillnotusuallyleadtostainingbyfungi;however,otherfungalproblems(moldfungi,whosesporesaremorereadilyairborne,anddecay)willdevelop.Becausethediscolorationscausedbysapstainersextenddeepintothewood,theycannotberemoved.

Bluestain has penetrated the sapwood of this pine log. The heartwood is not affected. The stain cannot be removed but the log is still structurally sound.

Non-microbial StainsIn addition to sunlight and fungi, wood can be

discolored by chemical reactions. When a tree is harvested, the living cells within the sapwood continue to live for a while. These cells produce substances that can later oxidize and discolor the wood. Formation of these stains, which are also known as kiln burn, can be influenced by heating, and they may not appear until after kiln drying. The color and extent of the stain can be influenced by species (e.g. brown stain is charac-teristic of white pine and sugar pine) or localized variations in moisture content (e.g. sticker shadow or sticker stain under, or adjacent to, the spacers that separate boards in lumber piles). Regardless of the color or pattern, non-microbial stains do not weaken wood and will not expand after the wood is seasoned.

Some species of wood, including oak and ce-dar, can also become discolored when chemi-cals in the wood react with iron. Iron is present in sawmill processing equipment and in nails. Stain-less steel, hot-dipped galvanized or other protect-ed screws and nails should be used on exposed wood surfaces to minimize iron stain. Iron stains can be removed from wood using an oxalic acid solution. (For more information on these discol-orations, please refer to Chapter 16 in the Wood Handbook. The URL for the online version is listed in the references at the end of this manual.)

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Bleachingthesurfaceofthewoodmaymakethestainlessnoticeablebyremovingandlighteningthecoloredpartofthefungus.Applicationofpigmentedfinishtothesurfaceofalogcanalsohidethepresenceofthestain.

Decay FungiUnlikemoldandstainfungithatcandiscolor,

butdonotweakenwood,woodrotters–ordecayfungi—consumepartsofthewoodcellwall.Therearemanyspeciesofdecayfungithataregroupedbytheappearanceofthewoodafterattack.Thetwomaintypesofdecayfungiarebrown rotandwhite rot.Regardlessofthetypeofwooddecay(or

This log has been weakened by fungal decay. Butt joints are especially vulnerable areas because water that enters the joint is absorbed by the porous end-grain of the logs.

thecommonnamesthatareusedtodescribeit),allrequirethatthewoodbewet.

Brownrotfungiutilizethecelluloseandhemicel-lulosesinthewoodcellwall.Abrown,crumblyresi-dueofligninisleftbehindandthusthenamebrownrot.Brownrottersaremostoftenassociatedwithsoft-woods,buttheycanattackhardwoods,too.Whiterotfungitendtoeatallcomponentsofthewoodcellwall;and,whenadvancedwhiterotdecayispresent,thewoodisturnedintoawhite,stringymass.Bothwhiteandbrownrotfungidestroythestructuralintegrityofthewood.Significantstrengthlossescanoccurintheveryearlystagesofattack,evenbeforevisualindica-torsarepresent.Fortunately,whendecayispresent

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Dry Rot Isn’t DryWater is the basis of life. This is true for animals

and plants, and it is also true for the fungi. So what do people mean by dry rot? Usually when wood decay is identified as dry rot, it is a misiden-tification of brown rot. In the advanced stages of brown rot, all that remains of the wood is a spongy brown material that can easily be broken by hand. If this dries out after the fungus has run its course, the dusty, crumbly residue will then be both “dry” and “rotten,” but it is still correctly re-ferred to as brown rot.

Most decay fungi feed on wood that is ex-posed to a steady source of water. This can oc-cur if wood is in contact with the ground or if a leak in a building traps water in contact with the wood. There are however a few, relatively rare fungi that can transport the needed water to the wood. These species may be called the dry rot fungi, but they are actually water-transporting brown rot fungi. Meruliporia incrassata, or “Po-ria” is one such fungus that is found in the United States, in particular in the southeast and south-ern California. Poria produces specialized water-conducting tubes called rhizomorphs that can transport water from wet areas (e.g. the ground) to nearby wood.

Poria is very susceptible to drying out (desic-cation), so it is unlikely to become established on wood that is in a dry environment. Poria gains ac-cess to a home because of construction details that allow the water-conducting rhizomorphs to reach wood members without drying out. Rhizo-morphs are initially small and grow only in diam-eter once they become established. This is one reason why they are susceptible to dehydration. Examples of construction details that allow ac-cess to the structure include siding that extends below grade, a humid crawl space, low earth-to-wood clearance and planter boxes that are attached directly to the exterior wall.

Wood is a remarkably durable material, and wooden buildings exist that are many centuries old. The key to this longevity is keeping the wood dry. This not only prevents attack by decay fungi but also prevents mold and stain and reduces the risk of insect infestation and weathering.

atthislevel,theextentofdecayisusuallylocalized,withmostofthememberbeingsound.

Therearetwopracticalmethodsforpreventingrotofwood:1)keepthewooddry(below25percentMC,thenominalfibersaturationpoint),or,incaseswherethatisnotpossible,2)makethewoodtoxictothefungus.Woodthatiskeptoutofcontactwithliq-uidwater—i.e.,insideorundercoverandnottouch-ingtheground—willremaindryenoughthatdecaywillnotbeaproblem.Inareaswherewettingisun-avoidable—forexample,deckinglumberorpostsintheground—preservativescanbeaddedtothewoodtoconsiderablyextendtheusefulservicelifeofthewoodmember.Theheartwoodofnaturallydurablespeciescontainsnaturalpreservativesthatcanhelpprotecttheheartwoodagainstinsectsandfungi.

Wood Protection for Log Homes

The Importance of Keeping Wood DryAloghouseisashowcaseforthenaturalbeauty

ofwood.Imperfectionssuchasknotsandcolorvariationsarepartofthisbeauty.Likewise,checkingandsettlingarenormalfeaturesoflogwalls.Theseirregularitiesareuniquecharactermarksthatshouldbeaccountedforindesignbutotherwiseembracedaspartoftheloghomelifestyle.

Themostimportantfactorinprotectingwoodiskeepingitdry.Woodthatisprotectedfromlong-termwettingwillnotbeattackedbyfungiandwillbelessattractivetowood-inhabitinginsects.Mostofthestepsthatcanbetakentokeepwooddryaretakeninthedesignstage,e.g.,byhavinglargeroofoverhangs(andadesignthatkeepsthelogsfromextendingbeyondthatoverhang),keepinglogwallswellabovegroundlevel,andprovidinggooddrainageawayfromthefoundation.

Properconstructionpracticesarealsoimportanttoensurethatwateriskeptoutofthebuilding.Wallpenetrations(e.g.,holescutforelectricalwires)andopeningssuchaswindowsanddoorsareareaswherepoorinstallationandmaterialchoicesoftenresultinleaksinthebuildingenclosure.Aftertheloghomehasbeendesignedandbuilt,timelyinspectionandmaintenanceplaysanimportantroleinkeepingwooddry.Guttersshouldbekeptcleantoavoidoverflowingandallowingwaterto

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protectionisrequired.Variouschemicaltreatmentsareavailableforprotectingwoodfrominsectsandfungi.Theproperwoodpreservativechoicedependsontheintendeduse.Withtheexceptionofafewover-the-counterpreservativesandmold-inhibitingchemicalsthataresometimesincludedinfinishes,homeownersdonotapplywoodprotectingchemicalsthemselves.Woodpreservativetreatmentsareeitherappliedduringthemanufacturingprocessfortemporaryprotectionagainsttemporaryproblems(e.g.,anti-sapstainchemicals),ortheyareappliedtowoodusingspecialequipmenttoprovidelong-termprotection.Themajorwoodpreservativetypesaredescribedbelow.

Sapstain chemicalsAsdiscussedabove,sapstainorbluestainare

fungithatcanrapidlydiscolorthesapwoodoffreshly-cutlogs.Somemanufacturersdiporsprayunseasoned(debarked)logsorlumberwithpreservativestoprovideprotectionagainstsapstainfungi.Thissurfacetreatmentisdesignedtoprotectthewoodtemporarilyuntilthesurfaceisdryenoughsothatsapstainisnolongerarisk.Therearemanytypesofsapstainchemicalbutnoneofthemprovideslong-termprotectiontowood.

Restricted-use preservativesDecayfungiandtermitescausestructuraldam-

agetowood,soitisimportanttoprotectagainsttheseorganismsifexposedwoodisgoingtoberepeatedlywetted(e.g.,exposeddeckingandtheunderlyingstructuralsupportmembers)oristouch-ingtheground(e.g.,columnsandposts).Anumberofheavy-dutypreservativesystemsareavailabletoprovidelong-lastingandeffectiveprotectionforwood.Creosoteandpentachlorophenolaretwodark-colored,oil-basedpreservativesthatareusedtoprotectrailroadtiesandutilitypoles.Creosotehasastrongsmell,andbothpreservativesleavethewoodwithanoilysurface,soneitheriscom-monlyusedinhomes(oldcreosote-treatedrailroadtieshaveoccasionallybeenused).Anumberofcopper-basedpreservativesexist.Thesechemicalsgivethewoodthefamiliargreenishcolorthatcharacterizesthetreatedwoodcommonlyavailableinhomeimprovementcentersandlumberyards.Thesepreservativesarewater-based,sothesurface

This is an example of poor design. The log roof beams and their supports are exposed to wetting. Fungal attack is likely. Because of the greater permeability of wood in the longitudinal direction, fungal damage is especially likely to occur in the exposed logs ends.

splashonthewallsofthebuilding.Treesandshrubsshouldbekepttrimmedawayfromthebuilding.Crawlspaces,kitchens,bathroomsandotherhumidareasshouldeitherbevented,orspecificdesignmeasuresshouldbeimplementedtocontrolandlimitmoisturedevelopment.

Wood Preservatives (if you can’t keep the wood dry)

Asmentionedabove,keepingwooddryisoftenthesimplestandalwaysthebestwoodprotectionmethod.Insomecircumstances,however,extra

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ofthetreatedwoodiscleanandpaintable.Insomepartsofthecountry,treatedwoodisoftenusedfordeckingandexposedrailings.Treatedwoodisalsocommonlyusedforstructuraljoists,beamsandcolumnsthatsupportdecks.Treatedlumberisoccasionallyusedforframinghousesinareaswithhightermiteordecayhazards,butitisrarelyusedforthelogsofloghomes.Exceptwhenincorporatedintopressure-impregnated(treated)members,heavy-dutypreservativesgenerallyarenotavailabletohomeowners;thesetreatmentsareappliedinfac-tories,usingpressurecyclestoforcethechemicalsbeyondthesurfaceofthewood.

Coppernaphthenateisaneffectivewoodpreser-vativethatisavailabletothegeneralpublic.Thisdarkgreenorbrownliquidistheover-the-counter“woodpreservative”thatisavailableathardwarestores.Zincnaphthenateisalsoavailabletothe

Durable materials should be used when the wood cannot be kept dry. Preservative treated wood (bottom); western redcedar, a naturally durable wood (middle); and wood/plastic composite or WPC decking boards (top) are some of the options for exposed decks. Each of these materials should be used with care. Note that the inner core of the treated pine is not green in color. This means it was not penetrated by the preservative treatment and is relatively susceptible to attack by decay and insects. The western redcedar board contains sapwood (the whitish wood on the left-hand edge), which is not naturally durable. Wood plastic composites are not suitable for structural elements and some formulations have poor fire-performance characteristics.

publicandisclearincolor.Althoughcopper(orzinc)naphthenateiseffectiveagainstawiderangeofinsectsandfungi,thelimitedpenetrationavail-ablethroughbrush-onordiptreatmentsinthefieldprovideonlyslightprotection.Thisisbecausethechemicalstaysnearthesurfaceofthewood.Becauseitalsohasanodorthatisdisagreeabletosome,itsuseislimitedtoexteriorapplications.

Manufacturersoftreatedwoodsometimesrec-ommendafieldtreatment,suchasbrushingoncoppernaphthenate,toprovideextraprotectiononthecutendsoftreatedwood.Especiallyinwesternspecies,fieldcutsusuallyexposeanuntreatedcore.Inthesesituations,useofafield-appliedpreserva-tivewillsupplementthedurabilityofthetreatedlumber.Theamountofcopperincoppernaphthe-nateisspecifiedasa“percentcopperasmetal.”Themaximumamountavailableinanover-the-counterformulationis2percent(copperasmetal).Thisamountshouldbeobtainedtomaximizetheprotec-tion.Adiptreatmentwilltypicallyresultindeeperpenetrationthanabrushapplication.

Considerableworkiscurrentlyunderwaytode-velopnon-copper-basedpreservatives.Thesenewpreservativesgenerallyconsistoftwoormoreco-biocidestoenhanceprotectionagainstfungiandin-sects.Newgenerationpreservativescanbefoundinexteriorcoatings(e.g.,paintsandstains)andotheranti-sapstainandmoldformulations.

Boron-based preservativesBoron-basedwoodpreservatives(borates)can

alsoprovideprotectionagainstawiderangeofin-sectsandfungi.Borateshaveanumberofpotentialadvantages:theyarecolorless,odorless,havelowmammaliantoxicityandareinexpensive.Boratesdonotprovidegoodprotectionagainstmold,thusborateformulationsoftencontainanadditionalbiocidetoprovideprotectionagainstmoldfungi(anexampleofaco-biocide).Boratesarewater-soluble,whichmeansthattheycanbeappliedtothesurfaceofwetwoodandthechemicalwilldiffuseintothewetareasofthelog.Thisresultsinprotectionbeyondthesurface.Someloghomemanufacturersapplyboratepreserva-tivestologsusingapressuretreatmentcyclebutmostoftenboratesarebrushedorsprayedontotheexte-riorofloghousesafterassembly.Boratescanalsobeformedintorodsthatareinsertedintoholesdrilled

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intologs.Ifboraterodsareusedinyourloghome,theyshouldbeinsertedintoholesdrilledatanup-wardangletoavoidwatermovingintothelogdownthelengthofthehole.

Ifboratepreservativesareappliedtodrywood(moisturecontent<25percentornofreewater),theycannotdiffuse,andtheprotectionwillbelimitedtothesurfaceofthewoodortheareaaroundtheboraterod.Becauseboratesarewater-soluble,theywilleventuallymoveout(leach)fromwoodthatisexposedtolong-termwetting.Forthisreason,bo-ratesshouldonlybeusedonwoodthatisprotectedfromcontinuouswetting.Someborate-basedprod-uctscontainglycol.Glycolmayimprovetheefficacyofthepreservativeagainsttermites,butithaslittledocumentedimpactonthediffusionorretentionoftheborate.

Natural durabilitySometreespeciesgrowwoodthatisnaturally

resistanttoattackbyinsectsandfungi.Thisnatural durabilityisduetochemicalsthatthetreedepositsintheheartwoodasitisformed.Redwood,cypressandcedarareexamplesofspecieswithadurableheart-wood.Itisimportanttonotethatonlytheheartwood(theinnercorewoodfromthelivingtree)isdurable.Thesapwoodofallspeciesissusceptibletodecayandinsectattack.Theheartwoodinmostnaturallydura-blespeciesisdarkerincolorthanthesapwood,whichisgenerallywhiteortan.Barkshouldberemovedfromalllogsusedforloghomes—barkincreasestheriskofdecayandproblemswithinsects.

FinishesFinishes,whichincludepaints,penetratingstains

andwaterrepellents,areliquidmixturesthatarebrushedorsprayedontowood.Finishesarenotwoodpreservatives,buttheycanhelptoprotectwood.Fin-ishesservetwopurposes.Thefirstistoprotectthesurfaceofthewoodfromweatheringandshort-termwetting.Pigments(colorparticles)andotheraddi-tivescanhelpprotectthewoodfromdamagebytheultravioletraysinsunlight.Thewaxesandresinsinfinishescanhelptorepelliquidwaterandthuspro-tectthewoodfromweatheringandthewettinganddryingcyclesthatcaneventuallyresultinsurfacechecking.Thesecondfunctionofafinishistochangeormaintainthelookofthewood.Awidevariety

The Weathered Look — A Traditional Finish for Log Homes

In the past, log homes and other structures with exposed wood were often unfinished. These buildings quickly turned brown or grey due to the action of sunlight. But, because wood is very durable if it is kept dry and because weathering is a very slow process, some of these buildings have lasted for hundreds of years. So, if a log home is well designed and the discolored and non-uniform appearance of weathered wood is acceptable, the home owner can dispense with finishes altogether. This will save the homeowner the time and expense of finishing and refinishing, and will provide a traditional look to the home.

Only the heartwood of naturally durable wood species is resistant to decay and insect attack. The sapwood (the outer band of light-colored wood) of this eastern redcedar post has been almost completely destroyed, while the heartwood remains sound.

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ofpigmentcolorsandconcentrationsisavailable.Darkerfinishes,withmorepigments,providegreaterprotectionbutalsotendtohidethenaturallookofthewood.

Finishescanbeorganizedintotwogroups:film-formingandpenetrating.Film-formingfinishesincludepaintandsolid-color(orheavy-body)stains.Thesefinishesremainonthesurfaceofthewoodandoftencontainhighlevelsofpigmentsthatcanprotectthewoodandthefinishitself.Penetratingfinishesareabsorbedintothesurfacelayersofthewood;examplesincludesomewaterrepellentsandsemi-transparentstains.Penetratingstainshavetheadvantagethattheywon’tpeellikethefilm-formingfinishescan.Themostcommonfinishesappliedtologhomesarepenetratingsemi-transparentstains,whichhavesomepigmenttoprotectthewoodandprovidecolorbutalsoallowthewoodgraintoshow.

Waterrepellentscanbestand-alonefinishesorcanbeusedasaprimerbeforeapplyingotherfin-ishes.Thedifferenceisintheamountofwaxtheycontain,soitisimportanttoknowwhichtypeyouareusing.Waterrepellentscanalsocontainapreser-vative,whichisincorporatedtohelpcontrolmold/mildew.However,finishesarenottruewoodpreser-vatives,noteventhewaterrepellent/preservatives.Finishesareintendedonlytoprotectthesurfacefromliquidwaterandsunshine—theydonotprovidelong-lastingprotectionagainstinsectsorfungi.

This wood has been finished with a semitransparent penetrating stain. The pigments provide some color, but the grain of the wood is still visible. Similar finishes are commonly used on log homes. Refer to Chapter 16 in the Wood Handbook for more information on wood finishes.

Application of finishes & refinishingIngeneral,followingtheapplicationdirections

onthecontainerwillensurethebestresults.Generalfinishingtipsinclude:• Finishesshouldbeappliedtoclean,drysurfaces.• Avoidapplyingfinishesinveryhotorverycold

weather.• Completeentirewallsinoneapplication.Thisis

especiallyimportantwithpigmented(colored)finishestoavoidlap marks,whichcanrevealtheoverlapofdifferentapplications.

Finishesshouldbereappliedwhentheystopdoingtheirjob—thosefunctionsbeingsheddingwaterandkeepingthewoodlookinggood.Finishesdonotlastverylonginexteriorapplications:sixmonthstonomorethanafewyearsisanormallifetime.Theresidualwaterrepellentcharacteristicscanbetestedbysprinklingwateronthewood:ifthewaterdoesn’tbeadonthesurface,thetreatmentshouldbereapplied.Becausepenetratingfinishessuchassemi-transparentpenetratingstainsfailgradually,refinishingisaccomplishedbyapplyingnewfinishovertheoldfinish.

Refinishingfilm-formingfinishesismoredifficult;theoldfinishmustbescrapedandsandedtoprovideasuitablesurfaceforthenextapplication.Dependingonthefinishbeingapplied,aninitialprimercoatmayberequired.Followtheinstructionsthatpertaintothefinishbeingapplied.

Cleaningmayberequiredtoprovideacleanandattractivesurfacepriortorefinishing.Anumberofsuitablechemicalwashesareavailableforthisjob.Logswallscanalsobecleanedusingpressurewashersorsand(orotherabrasivemedia)blasting.Thesemethodsremovethesurfacelayersofthewood,socareshouldbetakennottodamagethewood.

The Durability PyramidAlthoughproperconstruction,durablematerials

andmaintenancearenecessaryforadurableloghome(i.e.,onethatwillperformwelloverthelongrun),startingwithadry designiscritical.

Dry designThespecificaspectsofdrydesignwillvary

somewhatonthetypeofloghomebutwillconsistofdesignmeasuresthatkeepwaterawayfromthewalls

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ofthehome(forexample,byprovidingforawideroofoverhang)andbyincorporatingwallfeaturesthatallowawettedwalltodry.2

Manyloghomesuseroundlogs,butlogscanbeprocessedintodifferentshapes(stylingandprofiling)withthebuildingstillbeingreferredtoasalog home.Forexample,logscanbeprocessedsuchthatavertical(flat)surfaceisobservedontheinsideand/oroutsideofthehome.Manytermsareusedtodescribehowthelogwilllookafterprocessing(eitherbeforeorafterconstruction).Logscantakeona“D”shape(flatonthetopandbottom,roundedontheinsideand/oroutside),flatonallsurfaces(squareorrectangular),fullyround,orroundwithaconcavebottom.Thefinalshapeofthelogwill

2This practice can be summarized by the “4 Ds” of wood con-struction: Deflection of moisture away from the exterior walls, Drainage of moisture, Drying of wetted materials and use of Durable materials. This concept was developed by researchers in Vancouver, Canada, in response to numerous water-related building problems in that city. More information can be found at http://www.durable-wood.com/pdfs/The_4_Ds.doc

determinehowthememberswillfittogetheratthehorizontaljointsandverticallyatthecorners.Regardlessofthelogprofile,thegoalisadrydesign—eitherpreventthelogsfromgettingwetinthefirstplaceorfollowadesignthatwillallowthewalltoshedwateranddryquickly.

Mostmoisturerelatedproblemsinhomesareassociatedwithwaterleaksatpenetrationsandjoints(i.e.,atwindows,buttjointsoflogs).Logs(andheavytimbersingeneral)havetheadditionalchallengeofthepotentialtodevelopcracks(checks)asaresultofstressesthatdevelopduringwettinganddryingcycles.Logstructuresusuallyhavemorejointsthanotherframedconstructionsystems,andsomorecaremustbetakenduringdesignandconstructionandalsoduringpost-constructioninspectionsaspartofaroutinemaintenanceprogram.

Careful constructionCarefulconstructionmeansthatallmaterials

andcomponentsareassembledandinstalled

Inspection& Maintenance

Durable Materials

Careful Construction

DRY DESIGNThe log home durability pyramid. Inspection and maintenance cannot compensate for bad design, poor construction details or the failure to use durable materials.

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properly.Poorinstallationcanresultinleaksatwindows,doorsandotherpenetrations.Watervaporcanalsobetrappedandcondensedinsidethebuildingenclosureifconstructiondetailsareoverlookedorincorrectlyapplied.Inloghomes,thelogswillconstitutealargeportionofthebuildingenclosure.Waterentryintothelogs(atcracks,buttjoints,etc.)willresultininternaldecayandpossiblyalsoinsectdamage.Carefulconstructionalsomeansthatconnectionswhererigidcomponents(doors,windows,studwalls)meetlogwalls,whichwillsettleduringinitialdrying,allowfortheinevitablemovement.

Durable materialsInlocationswherewoodwillinevitablybe

exposedtowetting,durablematerialsshouldbeused.Theselocationsincludeanygroundcontactexposuresaswellasdeckingandrailingsnotprotectedbyarooforcovering.Durablewoodproductsincludepreservative-treatedwoodandnaturallydurablewoodssuchastheheartwoodofcypress,redwood,cedarsandwhiteoak.

Theuseofdurablematerialscanalsoprovideanadditionallayerofprotectionforcomponentsthataremostlyprotectedfromtheelements.Theuseoflessdurablerawmaterialsputsmoreimportanceontheotherthreecomponentsofthedurabilitypyramid.

Inspection and maintenanceRegularinspectionandmaintenanceisalsoimpor-

tantbecauseofthedifferencesinservicelifebetweenthemanycomponentsandassembliesthatmakeupaloghome.Forexample,aroofcoveringwillnotlastaslongasthesidingofahome(thelogwallsinthecaseofaloghome).Inparticular,finisheshavearelativelyshortlife-spanandshouldbeinspected,andreappliedifnecessary,onanannualbasis.

Themostimportantfactorinprotectingwoodiskeepingitdry.Withthisinmind,maintenanceofaloghomeshouldfocusonpracticesensuringthatraindoesnotgetintothehouseandthatexcesswaterva-porisallowedtogetout(orpreventedfromgettingin,dependingontheclimate).Guttersshouldbekeptcleanandvegetationtrimmedawayfromthebuild-ing.Kitchens,bathrooms,basementsandcrawlspacesshouldbewellventedorventilated.Maintenanceshouldalsoincluderegularinspectiontofind—andfix—anywaterleaks.Evensmallleaksinarooforaroundawindowcanbringinlargeamountsofwater,resultinginbigproblemsthatmayrevealthemselvesfarfromthesource.Inspectionsshouldalsolookforevidenceoftermites—significantdamagecanoccuriftermiteactivitygoesundetected.

Modernloghomesarelarge,comfortableandattractivebuildings.Agooddesignthatiswellexe-cutedandincludestheappropriateuseofdurablema-terialswillensurethatonlyregularmaintenancewillberequiredtokeepaloghomestandingandlookinggoodformanyyears.

Durable materials should always be used when wood will be exposed to wetting. The decking shown here is made from preservative-treated wood; but the railing is made from non-durable, untreated wood. Despite the finish that has been applied and the end caps on the posts, this railing is at very high risk of decay.

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References

TheWoodHandbook.Adownloadablereferencewithinformationonwoodproperties.www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

WoodDesignFocus,Volume14,Number1,Spring2004.PublishedbytheForestProductsSociety(quarterly).

LogConstructionManual:TheUltimateGuidetoBuildingHandcraftedLogHomes.Chambers,R.W.2003.DeepStreamPress,RiverFalls,Wis.272pp.

Preservation&MaintenanceofLogStructures.PreparedbyTheLogHomesCouncil(www.loghomes.org/)aloghomemanufacturersgroup.Availablefordownloadathttp://www.loghomes.org/uploads/Preservation%20%20Maintenance%20of%20Log%20Structures%2010-15-03.PDF

TheLogHomeMaintenanceGuide:AFieldGuideforIdentifying,Preventing,andSolvingProblems.Schroeder,G.2003.TheCountryPress.Woodstock,Vt.176pp.

WoodDestroyingOrganisms.VailK.,Burgess,G.,Pless,C.andTaylor,A.[eds].2006.UniversityofTennesseeExtensionPB1703.76pp.Atrainingmanualforpestmanagementprofessionalsthathasinformationonidentifyingpests—seechapter2.http://eppserver.ag.utk.edu/pat/PATinfo/WDO/WDOindex.htm

WeatheringandProtectionofWood.Feist,W.C.Proceedingsofthe79thAnnualMeetingoftheAmericanWoodPreserver’sAssociation,79:195-205.1983.http://www.fpl.fs.fed.us/documnts/pdf1983/feist83a.pdf

Despite repeated applications of finishes and caulking, these logs are failing due to fungal decay. This wall is exposed to rain because of an insufficient roof overhang. Homeowner maintenance could not compensate for a poor design.

PB1767-1M-5/07E12-4915-000-015-0707-0101

Programsinagricultureandnaturalresources,4-Hyouthdevelopment,familyandconsumersciences,andresourcedevelopment.

UniversityofTennesseeInstituteofAgriculture,U.S.DepartmentofAgricultureandcountygovernmentscooperating.

UTExtensionprovidesequalopportunitiesinprogramsandemployment.

Protecting Your Log Home

Wide overhangs to keep walls dry.

Keepflammables away from under deck.

Trim back vegetation from walls to allow wood to dry. Eliminate tall, branching or dead vegetation to lower wildfire risk.

Build foundation well above ground line to keep bottom logs dry. Apply vapor retarder between top of foundation and sill log.

Vent moisture from humid areas inside house – e.g. bath and kitchen.

Use preservative-treated or naturally durable wood for decks and other exposed areas.

Install gutter and downspouts to direct water away from house.

Ensure sufficient access for emergency vehicles.

Maintain roof and flashing and clean away debris.