Moisture is an important issue

Shrinkage of RedOak between 18%and 6%. At the startof the test bothpieces ( 1 1/4” x 4”)had the same sizeand 18% moisturecontent. The upperpiece dried down to6%, whereas thelower piece waskept at the 18%.

(a)

Nobody would worry about moisture in wood floors orconcrete slabs, if it would not be for the ugly cupping,and bowing, milky finishes, mold issues and relatedhealth hazards. Regulations have been established toavoid mold. Customer complaints have made inspec-tors and contractors more aware of moisture problems.Who wants to look at a cupped floor?

For centuries wood has been used in buildings, as struc-tural material, for furniture, floors, moldings, etc. It looksbeautiful and can be shaped easily. It is strong enoughto carry a house on its shoulders and is constantly re-plenished by our ever-growing forests.

Wood has always been sensitive to moisture. It shrinkswhen loosing moisture and expands when absorbingmoisture.

Every board moves differently when the moisturechanges! Shrinkage depends on the pattern of the yearrings. Most shrinkage occurs in the direction of the yearrings. Minimal shrinkage occurs perpendicular to theyear rings. The different shrinkage factors within the sameboard cause warpage by pulling the board in differentdirections. Quarter-sawnboards (a) are stablewith very litt leshrinkage. Sinceonly a few quarter-sawn boards canbe cut out of a roundtree, these boardsare of high gradeand expensive.

Considering moisture problems, wood floors have al-ways presented a special challenge:- Tiny changes in each board add up to big changes,

when hundreds of boards are laid side-by-side.

cabinetry, furniture, wood floors 6-9%moldings, window frames 9%outside painting and sealing 14%construction lumber below 19% 19%

- After installation, all changes in moisture are comingeither from the top or the bottom causing cupping orcrowning. Cupping occurs when the top of the floordries out . Crowningoccurs when thetop layer of the floorabsorbs moisture.

To avoid problems, all moisture sensitive materialswithin the building envelope including the concrete floorslabs, subfloors and of course the hardwood floorplanks have to be dry. Otherwise, moisture will migrateinto the wood floor until an equilibrium has beenreached. One section being too dry or too wet can influ-ence the entire installation.

Another crucial factor is the relationship between airhumidity and wood moisture. Dry air will pull moistureout of the wood floor (cupping). Wet air will releasemoisture into the wood floor (crowning). These changeswill take place until an equilibrium with the surround-ing air has been reached. Following are some ex-amples showing the impact of relative humidity:Moist summers versus dry winters.

At 700F and 35% rel. humidity, wood moisture will reach 7%.At 700F and 75% rel. humidity, wood moisture will reach 14%.At 700F and 20% rel. humidity, wood moisture will reach 5%.

Using a Pin Meter and a Thermo-HygrometerPin meters such as the mini-Ligno E/D are well suitedfor checking the moisture in wood floors and subfloors.Thermo-Hygrometers measure relative humidity andtemperature. Comparing relative humidity and woodmoisture will tell you whether the floor planks are dry

Suggestedmoistureranges

well acclimated. Before taking moisture readings checkthe manual for necessary wood species corrections.Temperature corrections may be necessary if the woodtemperature is over 800F or under 600F. When you arefilling out a report make sure the name of the meter,the wood species and the temperature settings are in-cluded.

Using a Pin Meter with a Slide-Hammer Electrode

More advanced meterssuch as the mini-LignoDX/C can be used with aslide-hammer electrodeand accurately adjustedfor tropical and domesticspecies. For the floor in-spector the slide hammerelectrode comes in handywhen checking a subfloorwithout removing the floorplanks. When measuring“hard” hardwood floors, it

is easier to hammer the electrode pins into the wood thanpushing the integral pins on the meter into the wood.

Using a Pinless MeterThe advantage of having no pinholes is obvious whendealing with a customer, who does not want pinholes inhis floor. Pinless meters can easily detect wet spotsand trouble areas in wood floors. To obtain accuratemoisture readings, corrections for wood species are nec-essary. Pinless meters such as the Ligno-Scanner SDMhave those correction factors built-in. After setting thewood species, slightly press the meter against the flatsurface. Record moisture readings and wood speciessetting. For later reference, you can take a photo withan identification mark such as a doorframe in the picture.Then, in case of problems, the same spot can be foundeasily and moisture values can be compared with the

original readings. (Tem-perature corrections arenot necessary for pinlessmeters.) The Ligno-Scan-ner SDM has very uniquecalibrations for bamboo.This is the only meter onmarket which has bam-boo calibrations.

Selectable Measuring Depth in Pinless MetersThe thickness of wood matters for pinless meters. Mostpinless meters are calibrated for a measuring depth of3/4”. When measuring wood floors less than 3/4” thick, themeasurements will include part of the subfloor or the con-crete underneath. This can be avoided by using a metersuch as the Ligno-Scanner SD with selectable measuringdepths 1/4” or 3/4” deep. In addition, the Scanner SD canbe used to check engineered floors thoroughly, becausethe top layer can be measured independent from the back-ing. Choosing the 1/4” depth is also recommended whenchecking the dryness of waterborne finishes.

Using the RH Method for Moisture in ConcreteThe NWFA Installation Manual states that readings fromnon-invasive scan meters or pin meters should not beused to determine if a concrete slab is dry enough to put awood floor down. The in-situ RH test and the Calcium Chlo-ride test are recommended.

Between those two tests, the in-situ probe test is more con-clusive because the moisture inside the slab is measured,whereas the Calcium Chloride test only considers mois-ture up to 1/4” deep.

RH Sensor is inserted into a sleeve andcapped off for acclimation. The capcan be removed at any time anda cable can be connected formoisture readings.

After the test is finished, the cable is connected again to pull the sensor outof the sleeve. The sensor can be used for further testing.

As always when installing a floor, allow the floor to ac-climate and check the moisture top and bottom beforestarting the job.

Proper Storage: All floors should be stored in a closed-in area with a controlled climate. If stored in a dampplace, dry wood will pick up moisture from the air. Checkrelative humidity and temperature in the warehouse, orother storage areas and compare to the moisture con-tent of the floor planks.

Proper Acclimation: Manufacturers of wood floors andthe NWFA organization suggest allowing time for accli-mation before installing a wood floor. During acclima-tion the room climate should be the same as after-wards when the room is in use.

Seasonal Changes: Depending on the climate in yourarea, summers may have a high relative humidity andwinters may have a low relative humidity. Unless aHVAC is operated year round the moisture in the woodfloor will follow the outside climate. During dry wintermonths tiny cracks may appear which disappear dur-ing moist summers. As mentioned before the extent ofthis “natural” moisture movement depends on woodspecies and grade.

If you want to determine the climate changes through-out the year for your area measure the same floor sec-tion in your home, shop or office once every month.After 12 months you have a series of moisture mea-surements that reflect seasonal changes.

Repair of Moisture Defects: For short moisture intru-sions, the damage can be superficial and may disap-pear after the floor has been dried out to its originalmoisture content.

If floor planks were not dry at the time of installation orabsorbed extra moisture later on, the floor may be cup-ping or crowning. In some cases the floor can be re-paired by resanding and refinishing, but only after ithas been confirmed that the floor is dry now.

If defects are so severe that permanent damage to thestructure of the wood has occurred, there is no cure.The floor has to be replaced. Therefore, moisture prob-lems have to be avoided before they occur.

Measuring the moisture is one important step wheninstalling floors of lasting beauty.

Helpful HintsCommon Causes for Moisture Problems- Floor planks were not dry when installed.- Subfloor was too wet when installed.- Existing or new concrete slab was too wet.- Water spills or leaks.- Ambient conditions see listing on page 2.

Record Keeping and Problem Diagnosis: In case ofcomplaints the question always comes up, who is toblame. The problem may be very obvious, but the causefor the problem is often hard to find:The home owner turning the air-condition off, the floorsupplier delivering wet floor planks, the installer mak-ing mistakes, the contractor not checking the concreteslab, and so on. Taking moisture measurements andkeeping notes is important at every step until the job iscompleted.

Buying Wood Floors: Upon delivery, check the mois-ture content. Notify the supplier promptly, when the mois-ture content is not right. If you wait too long, the suppliermay not accept any claims and put the blame on im-proper storage, while the floor was in your care.

Selecting a Wood Species: Not all wood species shrinkthe same. Unfortunately, more shrinking is always ac-companied by more warping. In entranceways, kitch-ens or bathrooms, it may be advisable to choose morestable floor planks of a higher grade to avoid problems.One rule applies to all floor planks: The more parallelthe grain runs to the edges of the board, the less cup-ping, crowning or shrinking can be expected. (See pg 1)

Engineered Floors: Not all engineered floors look likethis. Two problems were found in this floor plank andsorry to say, there was no cure: The floor was manufac-

tured before the toplayer and the backingwere dry. When thefloor planks dried out,the multi-layeredbacking did not shrink,

but the top layer shrank considerably, pulling the edgesup. The 8” width of the planks made matters worse.

When selecting an engineered floor, consider the widthof the floor planks and the shrinkage factor of the toplayer. The higher the shrinkage factor, the more sensi-tive the floor will be to moisture changes. The multi-layered backing is usually stable.