Spray in-place Concrete Fence

8/13/2019 Spray in-place Concrete Fence

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How To Build A Spray-In-Place

Concrete FenceWith Appendix Added Spring 2012


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Before

After

A spray-in-place concrete

fence adds a beautiful

touch to any yard. Not

only does it delineate, but

the fence also give a beau-

tiful backdrop to landscap-

ing. This fence by this

home in Italy, Texas varies

from six to four feet tall.

Disclaimer. All of the information given in this booklet is to the best of our knowledge factual and useful. The engineering data

given is from practical experience. Any person building these fences is advised to have each particular fence engineered by a profes-

sional engineer competent in this type of endeavor. The engineering will of necessity take into account the soil bearing, snow loads,

wind loads, seismic values, etc.

How To Build A Spray-In-Place

Concrete Fence


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Step 1Design the Fence Layout

Where is the property line?Whenever a fence is built, it

should be ascertained where the prop-

erty line is, or at least, exactly wherethe fence is to be constructed.

If the fence is between two prop-

erty owners it is best to have an agree-

ment on what the fence is to be like,

how it should be laid out, and who is

to pay for and install it.

The laws on fences vary from

state to state, so if you dont get an

absolute agreement with your neigh-

bor, it is probably best that you check

with an attorney to see what your legal

options are.

The property line must be determined, agreements between neighbors must be reached,and a plan decided on before constructioncan begin.

The zigzag fence is superior to the straight line fence. Notice the zigzag fence only requiresa fence post every 16 feet, while the straight line fence requires a post hole every 8 feet.

After locating and marking the

property lines decide with the neigh-

bors on the best fence layout. This is

doubly important if the fence is to be

zigzag.

During planning remember to

design the layout so it does not hinder

future plans, remodeling, or expan-

sions. For instance, if there is no exitto the back lot and some day you want

to build a swimming pool there, you

will nd it very difcult to go through

the concrete fence. Therefore, a gate

would be in order.

Fences perform many functions,

not the least is to keep them out

and us in. Them can be critters,

people, wind, snow drifts. Us usu-

ally consists of the residents and the

pets of the home.

An appropriate fence height


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Straight Fence vs. ZigzagFirst you will want to decide

whether or not to build a straight fence

or one with a zigzag. Both types of

fences, the straight line and the zigzag,

have advantages. You must decide

which of the two fences is most appro-

priate for your application.

The Straight Fence AdvantagesThe straight line fence is the tra-

ditional fence. It obviously can follow

precisely along given property lines,

and is utilized in most neighborhoods.

The straight fence has a series

of posts, in line, all standing verti-

cally. These posts acting together, in

concert, keep the fence standing and

prevent it from tipping over, even

when loads are applied, such as: high

winds, some one backing into it, or

something piled against the fence.

A straight fence has the advantage

of taking the least amount of land and

being an exact delineator between two

properties.

The Straight FenceDisadvantagesThe straight fences main disad-

vantage is strength. Expansion and

On a straight line fence(right) the wind pressureand vibration can oftenenlarge the post holes andeventually push the fenceover or snap the posts atground level.

Because of the zigzag,pressures act very differ-ently on this fence (below)from those of a straightfence. The 2 thick fencewith a one foot offsetzigzag acts as if it were atwo foot thick fence. Pres-sures applied act to turnover the fence rather thanto break it off at groundlevel. It is much morestable

needs to be established. Here again

it is wise to check your local city

ordinances. In many places a fence

over three feet tall in the front of the

house is not allowed. In other places

a fence has a maximum height in the

back of eight feet. You will nd the

fence ordinances vary everywhere in

between. Normally a six foot fenceis acceptable for everything but front

yards, where they may be hazardous

to motorists, especially on a corner lot.

The best choice is get the rules.

The spray-in-place concrete fence

is amazingly versatile. There are many

creative options for layout and design.


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Well laid-out plan for a zigzag fence (above). It would be even better if the ends of the fenceby the driveway had doubled fence posts, a box (see drawing page 5), or a turn to give greaterstability and a more nished look.

contraction is more severe especially

for long straight runs of fence. Twice

as many posts need to be installed

because they are all that hold it up.

The posts need to be a little larger in

diameter and be deeper in depth.

Consider wind pressure: A wind

blowing 100 miles per hour against

a vertical fence will push with 50pounds per square foot against the

fence. If the fence is six feet tall that

means there is 300 pounds of push

per foot down the length of the fence.

The taller part of the fence has a

lever action against the ground which

increases its propensity to roll over.

In other words, the taller the post

the more leverage it exerts. This 300

pound push is considered in average

three feet above the ground. If the

posts are eight feet apart and we havean average of 300 pounds of push,

that equals 2400 pounds of push on

one fence post.

That fence post must be able to

resist snapping off at ground level and

the post hole must resist enlarging to

prevent turn over at ground level. If

the hole starts to enlarge even a little

bit, the fence tends to pound the hole

larger and larger as the wind hits it

and backs off over and over again. A

fence that can withstand being tippedover from a one-time push may fail to

the buffeting of an intermittent wind.

It is therefore very important that the

post be larger in diameter and set deep

enough to withstand this turn over at

the ground line.

The Zigzag Fence AdvantagesThe zigzag fence is much stron-

ger and more durable than a straightfence. It will stand up to expansive

soils, wind loads and expansion and

contraction much better than a straight

fence. It proves interesting by being

Note the forms set up for shotcreting (left).This four-foot high fence is zigzagged onefoot off center each way. Surprisingly, whencompleted one hardly notices the zigzagsin this fence. The posts have already beenpoured. The bracing must resist wind untilthe fence is sprayed and solid.


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zigzagged, forming pockets for plant-

ing trees and shrubs. It can be taller

without signicantly increasing post

size.

A zigzag fence is a stronger fence

because of the zigzag. It acts as if it

were a wide fence. Note on the dia-

gram (see page 3) the pressures act on

a zigzag fence vastly differently fromthose of a straight fence.

When pressure is applied against

the top of the fence it tries to turn the

fence over. The posts certainly prevent

some turn over, but mostly they pre-

vent the fence from sliding sideways.

It is far easier to prevent a fence from

sliding sideways than it is to prevent

it from turning over. In order to turn

over the zigzag fence the wind must

pick up one whole side of the zigzag.

The amount of zig (off set fromcenter) determines how much pres-

sure will have to be applied before the

forward post can lift and bend over

against the back post. In other words,

the ability of the forces to hold against

pressure is much greater as the zigs

increase.

If the zigzagging is 2 feet every

16 feet the fence behaves as if it were

a two-foot wide fence. Air pressure

working against the fence is doing

more to lift the high side of the fencethan it is to turn over the fence. The

zigzag fence is enormously strong.

The zigzag fence is a very pretty

fence, besides being very structural.

Small alcoves can have benches

placed in them. Trees and plantings

look great set in the enclosures of the

insets.

The zigzag also acts as an expan-

sion joint at each change of direc-

tion, providing greater exibility in

expansion/contraction situations. The

amount of the zig can be varied. A

four-foot fence many only need twelve

to eighteen inches of zigzag. A six to

eight foot fence might be better with

eighteen inches to two feet of zigzag.

The zigzag fence can easily be

built eight, ten, twelve feet high. The

straight fence is best kept at lower

heights. The zigzag fence gets along

very easily with posts 16 foot on

Above, an eight foot fence constructed forthe Christmas Festival in Waxahachie, Texashas walls connected to the fence to delineatebooths. More importantly, they signicantlyadd to the strength of the fence.

Anytime an adornment or offset can beadded strength will be added to the fence.This straight line fence has small offsetevery eight feet and nishes with a decora-tive and strengthening box at the end of thefence.


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center. The straight fence should have

posts 8 foot on center.

The Zigzag Fence Disadvantages

The zigzag fence takes up a littlemore space. If you want a zigzag

fence the neighbors must absolutely

determine where the fence posts are

going to go. To be fair the posts

should zigzag across the property line

so that each of the parties have the

same amount of property taken up by

the fence itself. It takes a little more

layout. It is somewhat nontraditional.

Summary of the Principle DifferenceThe major difference in the

strength dynamics of these two fences

is what it will take to knock the

fence down.

The straight line fence is held in

place by the soil. Force against the

fence does two things. One, it tries

to snap the post off. But, the con-

crete post is very strong. Secondly,

it tries to make the post hole bigger.

Force acting against the top of the

This particular fence starts with twelve feetstraight, then a two foot deep triangle onthe right, then twelve straight feet of fence,then a two foot deep triangle to the left, andcontinues with alternating triangular niches.These niches create wonderful landscapingopportunities for benches, roses, anything.This fence acts as a 4 foot thick fence. It isextremely stable under all conditions.

There are few limitations to creative design.One could build a variation of the above

using square offsets instead of triangles. Thefence can be built serpentine. The spray-in-place concrete fence allows for the imagination to run wild.

fence forces it to rock back and forth,

enlarging the hole. The fence, to a

certain extent, is only as strong as the

soil.

For the zigzag fence the dynam-ics are totally different. It is not a soil

issue, or snapping off of the posts.

Here, force acting against the fence

tries to tip the fence over. The posts

serve mainly to keep the fence from

sliding sideways in the soil -- the

fence itself is the strength. A zigzag

fence that zigs one foot off center one

way and zags one foot off center the

other acts as if it were a two foot thick

fence.

Soil Considerations: Moving GroundMany parts of the United States

have expansive soil. This means that

when the ground gets wet it expands

and when it dries out it contracts.

Where we are here in Italy, Texas,

it is extremely bad. The contraction

will pull all of the dirt away from a

post, or it may lift the post, or in the

case of the concrete fence, it may try

to lift the fence.

If you are building in that type of

soil condition, we suggest again that

you very seriously look at the zigzag

fence. If you dont look at a zigzag

fence, then look at a very sizable size

post. The four foot high fence would

have a three foot deep post. An eight

foot high fence would have a four to

ve foot deep post. The straight line

fence should have at least an eight

inch post. The zigzag fence could get

by with a six-inch post and in all cases

it doesnt need to be especially deep,

three feet would be just right.

If the soils persist in moving the

fence around, then you can dig the

soil out from under the length of the

fence and that should stop. I am hesi-

tant to dig out from under the fencein most areas because that invites ani-

mals to dig under the fence. In most

places there is not going to be enough

expansion or contraction to bother the

fence itself. You should just monitor

it and if it looks like it is going to be

a problem then dig out half of the soil

out from under it, or two thirds, or all

of it if you need to.


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The Top of the FenceThe top of the fence in general

should be delineated. This can be as

simple as a 2 x 2 runner along the

top of the form or can have an inter-

esting pattern fastened to the forms as

illustrated.

As the fence is sprayed the con-

crete is shot up underneath this top

nish board so there is a place to stop.

The imagination can be free on how

to nish the top. It could be made to

look like a picket fence, it could be

made to have a at top, or it could be

let run wild and have an organic look.

Corners, Inclines, and more...This fence is marvelously ver-

satile. The corners can be square,

angled or rounded. On an incline the

fence can come down in steps or can

follow the slope of the hill. The fence

easily spans ditches because of its

strength. It is simple to vary the heightof the fence for privacy or a favorite

view.

The top of the fence can have any desired nished shape. Likewise the fence itself isextremely versatile. On an incline it can come down in steps or follow the slope of the hill.


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The post should be poured up ush with the ground level or 1/2 to 2 above the ground level,then insert three vertical bars of #3 rebar. The fence post above is the thickness and depth fora zigzag fence. Fence posts poured in a zigzag pattern (below).

The next step in building either of

the fences is installing the fence posts.

Measuring The LayoutPull a string along the property

line to delineate it. Measure carefully

the distances along the string and from

the string for the proper zigzag or

other pattern.

Determine The Post

Size And DistanceThe posts are obviously key to the

fence standing up. The size must belarge enough to restrain movement in

the soil. If the fence posts are in line

they must be larger than for the zigzag

fence.

The size of the post is best deter-

mined by the type of the soil. If the

soil is sand and not prone to loosing

while wet, a 6 inch fence post may

be all that is needed. More than likely,

the fence post should be 8 inches

in diameter. If the soil is subject to

ooding and not much strength when

wet, the post may need to be built 12

inches in diameter.

If the soil doesnt have some good

side to side holding characteristics

then a straight fence is probably not

the best to build. The zigzag fence

may be used here, but may be even

increased to 3 foot zigzag on 16 feet.

The post hole is then of not much

importance, a 6 inch or 8 inch post

hole would be ne.The post for the straight fence

should be eight feet apart and for the

zigzag fence they can be twelve to

sixteen feet apart.

Installing The PostCare must be taken to ll the post

Step 2Install Fence Posts


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hole to the top with concrete. The

concrete of the upper part of the post

must rest securely on that poured in

the hole.

Into the near center of the post

should be placed three vertical bars of

#3 rebar, extending up to the top of

the fence. They should be arranged

in a attened triangle along the line ofthe fence. If the fence is higher than

eight feet the rebar should probably be

changed to #4 bar and the post holes

may need to be increased to 18 inches

in diameter for the straight fence; 8

inches will still be ne for the zigzag

fence.

The post should be poured up ush with the ground level or slightly above ground level(above) with three vertical bars placed near center. Using a the side discharge door of aMonolithic Integrator SL30 (below) makes lling the post holes astoundingly quick and easy.


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Place the forms vertical and two to three inches off the center of the post. Note (above)

the rebar coming out of the hardened concrete post are arranged in a attened triangle.Waferboard, 2 x 4s, and stakes for bracing (below) provide easy and inexpensive formworkfor this four foot tall fence.

The forms can be made of virtu-

ally anything that will hold still.

We have found a light framework

of 2 x 4 faced with 7/16 inch thick

waferboard makes inexpensive form-

ing for this fence.

If the fence is only four feet tall,the waferboard can be laid down

horizontally. If it is six to eight foot

tall then the waferboard must be stood

on end.

These form boards are called

single side forms. One side of the

forms we will call off side that is

the side where we are going to do the

least amount of spraying. It is the side

for the bracing. The near side is the

Step 3Form The Fence


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Step 4Attach The Rebar

Now that the forms are in place,

plumbed and staked, we can put the

rebar in place. The rebar should be #3

(3/8 inch diameter) and run approxi-

mately 18 inches each way.In general the rst layer of rebar

is the horizontals, but it can be either

the horizontal or verticals. Fasten the

rst layer of rebar by drilling a small

hole on each side of the rebar through

the form boards. Then push a tie wire

through the holes and twist it tight in

the back. It takes about 4 attaching

points per 20 foot length of rebar. The

rebar should be tightly attached to

these forms so that it doesnt wave and

wiggle.When it is time to remove the

forms cut the wires on the off side

which will free the form.

The top rebar should be about two

inches below the top of the concrete.

The bottom should be about two

inches above the bottom of the con-

crete and then spread out the rebar

in-between, evenly, but not to exceed

eighteen inches.

The vertical rebar can then be

applied over the horizontal rebar andfastened with wire ties. These should

also be spaced evenly but not to

exceed eighteen inches.

The post is the structural key.

Center the rebar so it fastens into the

rebar of the fence. Make sure there is

a reasonable diameter to the size of the

post as it comes out of the ground. It

can be thinned to the thickness of the

fence in the rst 2 to 3 feet above the

ground. The rebar from the fence posts

is spaced about three inches apart and

attached to the horizontal rebar.

(Above) Drill small holes above and below the rebar through the form boards. Fasten the rstlayer of rebar by wiring it to the off side. The rebar should be lightly attached to these formsso that it doesnt wave and wiggle. Keep the rebar square and neat. It takes about 4 attachingpoints per 20 foot length of rebar.

Left is a 6 tall zigzag fence formed with rebaattached, ready for shotcreting. Only a sec-tion of the fence is formed, the remainder wilbe four feet tall and formed later. At the fenceposts there are three lengths of vertical outof the post rebar spaced 3 apart instead ofone rebar every 18.


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Place the rebar 15 to 18 on center. Deter-mine the distance by spacing the rebarevenly between the post. In general the hori-zontal rebar is placed rst, but the rst layer

of rebar can be either the verticals or hori-zontals.

The forms are up with the vertical rebar inplace. Note the single 2 x 4 brace onthe near side of the form so there is a mini-mal amount of obstruction for the shotcreterOnce the horizontal rebar is in place the concrete spraying can commence.

The rebar should be evenly spaced but notto exceed 18 inches apart, and come up totwo inches from the top of the fence and twoinches from the bottom of the fence.


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Step 5Applying the Shotcrete

The next step is applying the

shotcrete. This requires a working

understanding of cement, shotcreting,

aggregate and your options.

Ingredients for a fence: sand, cement, water,ad mixture, and colorant for the nal coat.

The Monolithic Integrator SL30 attached toa skid loader is self-bucketing and easy toload up with sand.

Types of Portland Cement

Type I. Normal Portland Cement.Use this general all purpose

portland cement. It is available at

most lumber yards and cement supply

stores. Following is the long explana-

tion. It is here for those who wish to

know more.

This is a general purpose cementsuitable for all uses when the special

properties of the other types are not

required. It is used in pavement and

sidewalk construction, reinforced

concrete buildings and bridges, rail-

way structures, tanks and reservoirs,

sewers, culverts, water-pipe, masonry

units, soil-cement mixtures, and for all

uses of cement or concrete not subject

to special sulfate hazard or where the

heat generated by the hydration of the

cement will not cause an objectionablerise in temperature.

Type II. Modifed Portland CementThis cement has a lower heat of

hydration than Type I and generates

heat at a slower rate. It is mixed with

Type I in some locations. It will work

well if available.

Air Entraining Portland Cement.There are three types of air-

entraining portland cement corre-sponding to Types I, II, and III. In

these cements very small quantities

of certain air-entraining materials are

incorporated by intergrinding them

with the clinker during the manufac-

turing process. They have been devel-

oped to produce concrete resistant to

severe frost action and to effects of

applications of salt to pavements for

snow and ice removal.


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tors experience.

Concrete StrengthsNormally shotcrete is much

stronger than conventional concrete

because of several factors. First more

cement is used in the mix. Also the

impaction created by the air tends to

drive out the larger air spaces thusproviding a somewhat denser product.

Usually shotcrete will have a compres-

sive strength of more than 4,000 psi.

The concrete strength depends

greatly on the aggregate, the amount

of cement and the amount of water.

AggregateThe best aggregate for shotcrete

is a very even gradation from 3/8 to

nearly nothing. If any of the sizes are

left out that size must be replaced by

the cement creating a much harder

mixture to pump and work with.

Rarely in the United States do we nd

nice, even graded aggregate. Aggre-

gate that has been crushed is also

much harder to work with than river or

natural aggregates. The jagged edges

of the crushed aggregate tend to hang

up in the pumping process. Rarely do

we nd an even graded aggregate. So

generally we have to make the bestwith what we can nd in the locality.

Mix WaterWherever possible the water/

cement ratio needs to be held at .4 to

.45. This creates an extremely strong,

workable concrete. Sometimes addi-

tional water must be used to create

a pumpable mix. This is done most

often when some of the aggregate is

off-size or cracked. Theoretically the

slump test will give you an indicationof the water cement ratio. However,

with 3/8 minus aggregate slump tests

are very unreliable.

Slump TestThe slump test is performed by

lling an inverted cone with concrete,

then removing the cone and measuring

the distance the concrete slumps from

the original height. A slump test is an

The concrete is being poured over the frontof the Monolithic Integrator SL30 ConcreteMixer into the MudSlinger EHP 1500 con-crete pump (above). The mixer also has aside gate for letting smaller amounts out(below), such as would be needed for llingpost holes. The side dump is demonstratedbelow.


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Safe Operations and PracticesThe use of appropriate safety equipmentis required. This includes face shields, orsafety goggles, respiratory protection (asneeded) and waterproof gloves. Wet con-crete will burn unprotected skin. Shoesshould be water proof and provide physicalprotection to the wearer. The rst layer ofshotcrete should be about 1/2 to 3/4 of oneinch. After it is set, a second coat can beapplied to bury the rebar.

The MudSlinger GHP1500 concrete pump isan ideal size for building fences. This is avery simple pump and can be driven by run-ning an air compressor.

extremely valid measurement for con-

crete in the 5, 6 sack range with 3/4 or

larger aggregate.

Compressive Strength TestsCompressive strengths in the

conventional concrete industries are

performed by breaking cylinders that

have been lled and set aside for thatpurpose. A good correlation between

a series of cylinders is about 20%.

Unfortunately shotcrete doesnt test

very well in cylinders unless they

are special shotcrete cylinders which

are hard to come by. The most valid

system for testing shotcrete seems to

be the Windsor probe or spraying a 2

thickness that is later cubed and tested.

Cubed tests and Windsor Probe

tests are generally quite comparable.

The Windsor Probe is much easier asit is simply a matter of ring a bolt

with a predetermined charge into the

concrete and measure the depth of

penetration. It is somewhat destruc-

tive in that theres a small hole left

with a bolt sticking out of it. Cubed

tests are totally nondestructive unless

they are taken as cores. The major

problem with cubed tests is always

the question -- was the concrete cured

under exactly the same conditions that

are in the facility itself.

Concrete ThicknessEvery endeavor is made to make

concrete the proper thickness. This

thickness is gauged by the amount of

embedment on the steel and by the

experience of the nozzleman. It is

further checked and corroborated by

the calculations of the volumes needed

for the project. In general, however,

the thickness is less important thanproperly embedding all of the rein-

forcing steel.

When 1/2 inch to 3/4 inch of con-

crete covers the rebar on both sides, it

is thick enough.


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The shotcrete is placed in layers. The rst layer is left for several hours or overnight to gain

strength. Then the second layer can be applied, then, of course, the third layer. By the timethe second and third layers are in place the fence will be very strong.

Shown above the rst layer of concrete is in place. There are places where some of theconcrete sloughed off. These places will be easily lled in with the second layer of concrete.

Shotcrete Mix DesignMix Design for 1/3 cubic yard

Shotcrete mix design varies from

job to job due to different types of

materials and other conditions. How-

ever, following is a mix design that

works well in most areas.

Cement 188 lb. Two sacks of

standard Type I or II or I-II Portland

cement. This is what the lumber yard

will carry. It is not mortar mix.

Water about 80 lbs. (10 gal-

lons.) Water must be clean (potable).

To Mix or Not to Mix

Do you want to use ready-mix or

mix on-site? In order to use ready-

mix you will need a larger pump and

will want to have more of the fence

formed. Mixing on-site has advan-

tages, such as ease of pouring the

fence posts and convenient schedul-

ing.

Obviously, if the job uses thou-sands of yards of concrete, a ready

mix plant is the only way to go for

ordering shotcrete. But for the small

jobs using the small pumps, we sug-

gest you consider mixing on site.

Mixing on-site with small mixers

must be well organized. The mixers

can be a Porta-mix mounted on a skid

loader, or a plaster mixer, or small line

concrete mixer. The biggest advan-

tage of on-site mixing is the ability to

control the speed and delivery. There

is nothing worse than waiting a few

hours for the ready-mix truck and then

immediately having a breakdown that

prevents unloading it.


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The nozzleman applies the second layer ofshotcrete. One can see that the rebar isbeing buried with this second layer. Thefence is now approximately one and a halfinches thick. The rebar needs to be scrapedor ridges will be left. Do not apply all theshotcrete at one time. Cover the fence thengo back and do it again. After a sectionsets for even a short time it can often beresprayed.

(Below) The nozzle should be held perpen-dicular to the work or slightly pointed up asshown on page 22. Never, never spray downwith only one exception spraying the basefooting of the fence.

This will vary from job to job and

must be adjusted. The water in the

aggregate will cause a difference in

the amount of water needed. Adjust to

a proper slump. 2 to 6 as needed.

Concrete Sand 690 lbs. (Ten, 5

gallon buckets is a good approximate

measure).

Pea rock 140 lbs. (Two, 5

gallon buckets.) The amount of pea

rock is adjusted per gradation of the

sand. If the sand is high in larger

aggregate the pea rock may be left out.

If it is low, then more may be needed.

This is a place to start for maximum

strength. The total of the sand and

pea rock should equal the 830 pounds

(twelve, 5 gallon buckets). Usually,

the pea rock is left out of the nal

coats to provide a smoother nish.

Kel-Crete use 2 oz. minimumper batch. Try up to four ounces per

batch. Adjust between for the best

results. We normally use 2.5 ounces.

Add the Kel-Crete additive in with

the water for easier dispersion. If the

Kel-Crete is not added, another 1/3 of

a bag of cement should be added.

Nylon bers use 1/3 lb. Per

batch. These are the best bers we

have found for what we are doing.

Total weight of this batch will be

about 1,100 pounds.

Spray the ShotcreteThe posts are obviously key to the

fence standing up. The size must be

large enough to restrain movement in

the soil. If the fence posts are in linethey must be larger than for the zigzag

fence.

The concrete of the upper part

of the post must rest securely on that

poured in the hole.

Blow and clean any material off

the top of the lower portion before

shotcreting the upper portion.

And be sure and spray onto the

top of the post immediately (rst) to

prevent rebound or other materials


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21

The fence is now structurally strong. It needs one more layer to even it up and then thenal layer of colorant.

After the forms are removed spray another 3/4 inch to both sides of the fence. After this hascured a few hours nish the fence with a 1/4 inch thick coat of concrete with colorant added.One can choose to nish with the gray concrete and stain it or just leave it gray. This nalcoat can be etched to simulate rock, brick or block nish.

to accumulate between the layers of

concrete.

Once all of the form work and

rebar are in place a light coating of

concrete is sprayed onto the form

through the rebar.

The placing of the concrete is

simple when done right. Apply the

concrete as evenly as possible at all

times. This helps in keeping the thick-ness correct.

The shotcrete is started at the

bottom. The entire footing (top of

posts) should be covered rst with a

thick layer that extends about 1 foot

up the wall. This is to make sure

that the concrete on the footing is

good concrete and not just shotcrete

rebound.

This rst layer of concrete

includes the nylon bers to make the

mix stick better. The idea is to cover

the plywood completely and to build

up some on the rebar.

It is not necessary that this rst

run of concrete be very thick. If it is

working very well and sticking well,

then go ahead and put a 1/2 to 3/4 inch

on it. If all you can get to stick is a

1/4 of an inch, that is ne.

Let this concrete set over night,

or until there is approximately 600 psi

strength. This concrete will be tough,but it still can be scratched with a key.

If the weather is inclement let the con-

crete set for two days. If the concrete

is going to be subjected to severe rain

or frost it will need to be covered. If

it is real cold then it will need to be

heated between the covering and the

concrete surface.

The next day spray the fence

again with concrete, bringing the total

thickness up to about an inch and a

half. This may take two spray ses-sions. Often it can be sprayed twice

the second day.

Build the fence out, embedding

the rebar very thoroughly. Care

should be taken to scrape the rebar

after each spraying of the concrete so

it does not have a large build up on it.

The rebar needs to be embedded

in the concrete with about a 1/2 to 3/4

inch of cover. The spraying process

the second day doesnt need to get it


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22

Here can be seen the layering of the fence.The fence on the left has two layers of shot-crete and the forms have been stripped. Thesection on the right still has forms in place,some of which has been sprayed with therst layer of concrete.

With the forms removed from the back, andthe third coat applied, the fence is now readyfor the nish coat of colored concrete. This

is the time to consider etching the fence tolook like a rock wall.

out to full thickness because we are

going to spray one more time with the

colored concrete. The second day it is

a good idea to have most of the thick-

ness nished up. You dont want to

spend a lot of time with colored con-

crete trying to cover up missed places.

Note: It is very difcult to judge

the depth of sprayed concrete as it is

being applied. A 1 layer can look

very much like a 1/8 layer. To be

sure of a uniform build up of thick-

ness, a very uniform spraying pattern

should be followed. This pattern can

vary according to the nozzleman, but

it should be consistent. To insure

proper thickness, check the depth

gauges.

It is important to use good shot-

crete techniques when shooting around

rebar, that is, shoot from close enoughto the bar and with enough force that

the concrete cannot build up on the

face of the bar but closes around it

from the back.

After the fence has set overnight,

gently, and I use the word gently,

remove the forms, clean them, and

move them on to get ready for another

section of fence.

The Last Coat

The concrete can now be appliedto both sides of the fence. This last

coat of concrete to the front side and

the complete coating on the back side

should be done with a half to three

quarter inch covering.

This spray of approximately 1/2 to

3/4 inch of concrete on the form side

is to protect the rebar.

The fence will harden up consid-

erably over the rst thirty days. It is

very helpful if it can be kept damp

within that same thirty day period.This can be done by hanging cloth or

burlap over the fence and spraying

water on it from time to time during

the day. It is extremely important that

the fence be kept moist during periods

of direct sun, hot sun, and dry winds.

The fence can be protected by coating

with a concrete sealer available from

the concrete accessory supplier.


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23

It is a good idea to keep the fence moist,as with any concrete, as it goes through its

curing phase. If possible the fence shouldbe kept wet for up to 30 days or a concretecuring compound can be used. These com-pounds can be purchased from a concreteaccesory store.

Final color coat sprayed is on the left. Notethe position of the nozzleman for properspraying. The nozzle should be held per-pendicular to the work or slightly pointedup as shown both above and below. Never,never spray down with only one exception spraying the base footing of the fence.

ColorThe colorant will give a pleasing

color to the nished concrete fence.

Spray a quarter inch of colored con-

crete on both sides to produce the nal

nish.

If the nal coat of shotcrete has

colorant in it, the fence is now n-

ished other than the moisture cure.

There is nothing that says that thegray is not beautiful. Gray colored

concrete will eventually get white and

become very pretty.

The nal spraying of concrete

may be held up until the entire fence is

nished with gray concrete so that the

color can be the same from one end of

the fence to the other.

The coloring in concrete is always

a little bit tricky. It is difcult to get a

true match from one batch to another.

The batches tend to interfere with each

other. They seem to get more water

or something in one than they do in

the other, but after a period of a few

weeks it can be noticed that the fence

tends to equal out to one color.

An option, a very valid option, is

to spray out the full thickness of the

concrete in the gray and then use a

concrete stain. Most reputable paint/

concrete shops have concrete stain. It

is not a paint, it is a stain. It soaksinto the concrete and will give you a

permanent color nish.

If a really nice nish is desired,

the stain is probably the safest way to

go.


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This 8-foot tall, 800-foot long fence is for the annual Bethlehem Revisited program in Waxa-hachie, Texas. The fence encloses a half a block. It has concrete posts and wing walls toprovide lateral stability. These fence/walls can be built very cost effectively. The walls aretwo-inches thick, except at the posts where they are three and a half inches thick. Withoutcolorant it is a beautiful gray.


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AppendixIn the past 20+ years, we have

gained signicant know-how inbuilding spray-in-place concretefences. This Appendix adds to thatknowledge.

Zigzags: Experience has taught

us the importance of zigzags. Theymake a difference in strength, ver-satility, expansion and contraction.

Zigzags can be symmetrical,moving back and forth an extrafoot on each side of the propertyline, every 16. Half as many postsare needed with zigzag fence.

Or they can be even moreornamental. The fence can runstraight down the property line for12, then have a short zigzag thatcreates a planter box or a place fora yard bench.

First do the one side and thendo the other. If these are 4 long,zig it 2, rst to one side and thento the other. You can imagine thestability this gives a fence andmakes it very beautiful. Obviouslyneighbors need to agree on thefence, but it really creates a high-light for both properties.

Basalt Reinforcing: We havelearned to use basalt reinforcing.Basalt is another name for lavarock. Reinforcing made of basaltis twice as strong as steel and --most importantly -- it wont rust.The number one cause of concretefailure is rusting rebar. Water soaksthrough the concretes pores andeventually rusts the rebar. As therusts grows, it explodes the con-crete.

Protecting the rebar is one ofthe concretes major functions.Using basalt reinforcing has madea dramatic difference in the abil-ity to build the fence. We suggestyou use the basalt fabric. We callit a fabric. It has about a one-inch-square spacing each direction, andwe can take this and put it directlyinto the concrete as we spray.

We rst spray a 1/2 to 3/4of concrete on the fence forming.

After it sets up, we spray aboutanother 1/2. Then we just gently

push the reinforcing into that con-crete. After it sets up to where it isrelatively solid, we spray the next1/2 or 3/4 of concrete to nishthe fence.

At this point we have manyoptions: We can peel the formwork off and spray a light touchon the backside, or we can justleave it alone and do a hand trowelon either side, but in most caseswe are done.

Now is the time to decide whatto do about the fence color-wise.Concrete can have colorant mixedin with it. But if you have eversprayed concrete, you know itssuper tough to make the same mixwith each batch and get the samecolor. And the color in the concreteis less expensive and will stay thatcolor virtually forever.

We also can recommend coat-ing the fence with something likeH&C Concrete Stain. This stainseems to last forever and is gor-

Simple zig zag fence with colorant is 1 3/4 to 2 inches thick and six feet tall.

See the basalt webbing being installed. Simple, fast and permanent for ower boxes orfences.


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geous and self-cleaning. The fencelooks sharp and new for years.

The thickness described here is1 to 2 thick. Unless that fencewill be subjected to heavy loads orheavy banging, that is all the fenceyou will ever need. In fact, itscertainly stronger than any woodfence. And because we can keep itthin, we use less material and dothe job quicker, simpler and lessexpensively.

As part of this Appendix, wecan also tell you that you canuse #2 steel rebar in the fence, asdescribed in the book. I wouldmove the bars closer to 15 oncenter -- or you could even go to12. Number 2 rebar is not readilyavailable, but it can be used. But

if you use steel rebar you have tokeep the fence well coated to pre-vent rusting.

If you are using steel rebar, besure you have about 2 of coveron each side of the rebar to pro-tect it from water. Or you have topaint the fence to protect it. To doa really good job of painting thefence, you need something besidethe concrete stain. You need some-thing like silicone or rst class

acrylic that stops water migration.We strongly recommend that

you use basalt reinforcing. Therebar coming up out of the postscan still be steel, but it is evenbetter if its basalt as well. Basaltrebar can be purchased at the sameplaces as the webbing.

The zig zag prevents trouble ith the black clay soil. Fence is permanent.

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Spray in-place Concrete Fence