Burlap-crete explained

Tuesday, March 4, 2008 

[papercreters] Burlap-Crete

burlap75164

Burlapcrete is basically loose-weave burlap, soaked in a modified rapid setting cement. Is there any advantage to using burlapcrete instead of exterior plywood sheathing?  The potential advantages are: it doesn’t warp, swell, delaminate, mold, burn, get chewed through by rodents, requires fewer tools and skills to master, and can weather years of direct contact with the elements with no noticed adverse reactions (no warping, splitting, rotting, weakening, molding, no insect or rodent issues). Twenty minutes with a blowtorch does nothing. It’s resilient, not brittle- so a hammer blow bounces off. Later I’ll tell you exactly how to make it- but first a little history.

There are a few folks that have used burlap soaked in cement slurry and
 draped it over wire form-work, therefore being able to build a house with a similar approach as a large piece of sculpture- but I’ve found that burlap prepared this way is weak unless done in several layers. Another way that has been tried is 
to stretch the burlap over an armature and paint a weak cement
 solution on it, letting it dry, and adding five to ten layers– which takes about forever unless 
you have lots of people. I’ve tried a bunch of different mixes while researching how to make ‘burlapcrete’ and
 have come up with one that works so well its just about amazing!  My
 exterior walls on my 40′ diameter round house are made this way, 1,200 square feet.

clothespins7517
The yellow text reads: “Burlap pinched onto stock panels using oiled clothespins. Overlapping seams between sections of burlap blend together well with Cement-All.”

I found that portland and sand and water, in any combination generally
 don’t do well for burlap-crete, as the result is fairly easy to crack
 and then powders and seperates from the burlap. I tried adding latex
paint which was suggested on numerous web pages as a way to add 
elasticity, but it wasn’t very strong. I suspect in several layers 
either of these approaches could work, but I was looking for a thin
 shell that would be strong enough to use as a wall without building up layer after layer… I tried plastic cement, which is a bagged cement
 product with clay and other plasticizers and it worked fairly well,
 I mixed 2 parts medium grit sand and 1 part plastic cement. However, it 
takes a long time to dry so any movement or wind at your work site could keep the burlap moving while it sets up, and then you have a dry, powdery piece of burlap waving in the breeze. In two layers this mix is only so-so for strength and it does crack easily when moderate pressure is applied. Then I 
tried traditional sculpture recipes using 20 minute casting plaster,
which in two layers was generally stronger than the cement-and-burlap
 products, and was rock hard in 20 minutes. The problem with that stuff 
is it isn’t weatherproof at all, and dissolves in damp conditions so I was concerned about water vapor condensating in the wall, as it will 
in any structure when the outside temperature is lower than the inside temp 
unless you have a vapor barrier paint on the inside of your walls or
 something similar. So then I tried 5 minute post hole cement, which 
failed miserably but did set up rapidly. It crumbled and powdered into
 oblivion very readily when even mild pressure was applied by flexing the sample by hand. I tried a
 bunch of other things, and finally tried rapid set non-shrinking grout (Cement-All brand), which in two layers (one layer half overlapping the next like
 shingles) is very strong, about as rigid as 1/2″ plywood coated with stucco. You can crack it with a lot of force or a hammer blow, so I
 added latex conctrete binder to the mix and that added a fair bit of elasticity to it so that when it dried, it was tougher and when enough
 force was applied to break it, it would bend slightly before breaking,
 and only a fine hairline crack would appear as opposed to a large
 shattering pattern. In 30 minutes it achieves 3,000 psi compressive
 strength, 6,000 overnight, and 9,000 after 28 days. (That’s what the bag says, Cement-All fast set non-shrinking grout.) It sets up
 underwater, is highly durable in wet locations, and has a sandy beige 
color when dry. The seams between pieces of burlap feather into each 
other and disappear, and when dry all it takes is dampening to be able
 to blend another layer of burlap-crete onto it without any cracking
 and the splice becomes invisible. If you add too much concrete binder
 (a latex glue), it will shrink when drying and cracks will appear, so I misted the walls for half an hour while drying, and came up with appropriate amounts of concrete binder to add.

Burlapcrete attached to stock panels on round house.
Burlapcrete as seen from inside of building.

Cement-All sets up 
quickly, and if you use a plastic or metal bucket you won’t have the bucket very long. Get a rubber feed bucket from a livestock supply business, a big one about three feet around
 and a little over a foot high. That way when the stuff turns into rock
, which it will until you find out what mix to use for your climate, you
 can flex the bucket and the stuff will drop out. I tried it on cold 
days and warm days and windy  and sunny days: each time I needed a 
different amount of water. Sometimes the water coming out of my hose was hot, and that changes the setting time as well- too hot and the stuff turns to rock while you’re still mixing it. The basic mix I found worked well was to 
use a plastic 5 gallon bucket to mix it in and then pour it into the
 rubber feed bucket for use with the burlap. The sacks of Cement-All 
are 55 lbs. and you can mix a sack in a 5 gallon bucket, but as soon as
 you’re done mixing, pour it into the rubber bucket and clean your 
plastic one immediately. Using a 1/2″ drill with a mixing paddle is
 probably mandatory- a drill with a small motor will not have the torque required to mix this stiff solution. I hung my half inch drill from a rope at a comfortable working
 height so all I had to do was pull the trigger to mix the stuff. It
 depends on the brand of concrete binder as to how much of the stuff to
 use. Sika brand required 3 quarts of binder and 2 quarts of water per
 55 lb. bag of Cement-All grout. Supercrete brand concrete binder is a
 lot thicker, and slightly less expensive, so that I can use 1 quart of
 it and 5 quarts of water. Put the binder and water in your plastic
bucket first, then pour half the sack of Cement-All in and stir with
 your paddle on a drill for about 30 seconds, add half of what’s left 
and stir again, and add the last of it and stir until creamy smooth,
 about a minute or two. Be sure you’ve got your burlap soaking in water
 overnight, cut into pieces that will more-or-less fit in your big
 rubber feed bucket, about two-feet square works good. Wring it out a
 little and dip it in, working the Cement-All into it from both sides 
by turning the burlap over a few times. Work your hands around the 
bottom of the rubber bucket as the Cement-All will start to harden
 there but you can get it workable again by pressing it around with
 your GLOVED hands and it will mix with the water that’s soaked into the burlap. If 
it sets up too quickly, make sure your next piece of burlap isn’t wrung 
out so well, a little water goes a long way. Soupy is good, but don’t
 go beyond pea soup consistency in terms of making it more runny.
 You’ll need a ton of large wooden or plastic clothes pins to hold the burlap onto 
your wire wall, I used stock panels, but you could get really
 sculptural with this stuff by using a more flexible but still heavy gauge wire substrate, such as cyclone fencing material which will conform more easily when making compound curves and the like.

Because burlapcrete really does set up FAST, I put
 the clothes pins onto the wire about a foot above where I 
hang the burlap, so that it will be all ready to go the moment I
 need them. Oil the clothes pins, otherwise they’ll become part of your 
project on a permanent basis. To hold the middle of the burlap against t
he wire, press the clothespins around the wire trapping the burlap
 against them, this leaves an interesting divot in your wall, which can
 be filled later with more Cement-All if you don’t like the look of it.
 Seriously, if you overlap each layer half way, it ends up 2 layers
thick and is as strong as a ‘real’ house covered in stucco. Then you
 can do whatever you want inside, out of the rain and sun and wind
 while you finish your project. It’s non-flammable, too, and you can 
cut out the doors and windows as needed later on, using a cutting 
wheel or sawzall. I had been thinking of using it for a roof at about three 
layers thick, but it isn’t cheap at about $18 per 55 lb. sack, and my tests showed that more than 3 coats would be required and I settled on metal lath over stock panels, and non-rapid set construction grout modified with pva fibers as my roofing material. Back to Burlap-Crete in terms of wall applications: concrete binder is less than $10 per gallon, and only one quart is 
needed per bag of Cement-All if you use the Quickrete brand of concrete binder. In an overlapping pattern, a 
sack will yeild about 25 square feet of soaked burlap. One person can
 work quickly enough to deal with the entire process alone if
 pre-planning is employed. Wear a dust mask while mixing the stuff, its 
dusty. When hard, its fairly rough in texture, but by dampening it and
 then with a gloved hand, smoothing on a thinned out layer of Cement-All from the remnants of your rubber bucket full of
 stuff when there isn’t enough left to coat an entire piece of burlap,
 you can even out the contours and make the wall nice and smooth. You can 
also add cement coloring powder to a final coat and trowel it or glove 
it on.

A note on cost effectiveness: the materials cost for a section of wall including the heavy wire formwork aka stock panels, works out to about $1.44 per square foot as of October 2008.  This does not include the framework (rebar, 2×4, or etc.)  I calculated this based on a 50 square foot section of wall.

The components included:

     • 2 sacks Cement All, $18 ea.  = $36

     • 2 burlap totes, which are 49 square foot pieces of burlap @ $4 ea. = $8

     • 1/2 container (two quarts) concrete binder: $5

     • Most of a stock panel- they currently cost $23 ea in my area, so I estimated $18

Total: $72

Divided by approx. 50 square feet = $1.44 per square foot.


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34 thoughts on “Burlap-crete explained”

  1. Man, I really love your ideas. Do you think sand could be put into the walls ( between the burlap on the outside and whatever you use on the inside? Also could you use another form of material on the same framework such as plaster or ferro cement?

    1. To completely entrap the metal framework I have added ferrocement on the inside, attaching stucco wire to the stock panels with a hog ring gun. I’ve thought about ‘roman’ ferrocement- using roman cement for non load bearing applications much like a ferro-reinforced render or stucco. (Lime, sand, and clay). And yes, sand could be put between the walls for thermal mass, as could gravel or tamped earth (preferably with lime in the earth to discourage mold). The concern I’d have with sand, is that if a hole occurred in the wall, a lot of the sand could pour out.)

  2. In Australia there was a similar substance used in the Depression, called petrified hessian (ie petrified burlap). The ingredients were water, cement, lime, alum and salt. It set hard as a rock, was weatherproof and I saw some buildings dating from the Depression, as late as the late 1950s so it was also very durable.

    1. That sounds very intriguing! There was an architect in San Francisco who designed the Palace of Fine Arts for the 1915 Pan-Pacific International Exhibition named Bernard Maybeck who used something similar, “the palace’s beautiful Greco-Romanesque rotunda and the eight colonnades that made up the original Palace of Fine Arts were framed in wood and covered with a burlap-fiber and plaster known as ‘staff’.”Palace of Fine Arts

      Maybeck is also known for building houses out of burlap sacks soaked in “bubble stone” and draped on chicken wire. “The disastrous fire in Berkeley in 1923 destroyed many of Maybeck’s houses. In search of a cheap fireproof surfacing material, he tried coating burlap sacks with a foamy concrete mixture called “Bubble Stone.” This material, invented by a Berkeley man [John A. Rice], was produced by mixing chemicals with cement; it was so light in weight that a mass the size of a bale of hay could be lifted by one man.

      Maybeck’s production of Bubble Stone has been described by Jack Hillmer, San Francisco architect, who, in 1959, with Roy Flamm, photographer, prepared the first large exhibition of Maybeck’s work. The water and chemicals were mixed in an old washing machine, then Maybeck folded cement and sand mortar (without aggregate) into the froth ‘like adding sugar to whipped cream.’ Wet burlap sacks dipped into the mixture came out with about an inch of foamy concrete adhering to them. The coated sacks were then nailed to the studs and sheathing of a cottage, in which factory sash served as windows and as French doors to the garden. The total cost of the cottage was $600. It is still in use today, although the cement is chipping away from the sacks (McCoy 1975).”

  3. Kurt Billig in England used stretched burlap over arched frames to build Quonset-like storage structures during World War 2. The burlap was the onlky reinforcing on small structures.

    1. Small structures? Billig was able to produce arches with spans of up to 60ft using this non reinforced hessian method.

      further, Billig also created prestressed concrete, now used in massive arch bridges.and the like.

      Nice web page….wil look at rest of your site!

      Hows the structure holding up?

  4. Is the recipe complete as written. Is ther other chemicals that you could add to make it completely water proof and rust proof.
    I would like to make some smaller scale buildings: root cellar, water collection and out buildings. Thank You for any help you could provide I am sure no one would like to take the structures
    apart to rework them.

    1. To ensure water proofing and rust proofing, I would add a waterproofing agent designed for cement and concrete.I would suggest a product called “Anti Hydro NC” which is used for waterproof, dust proof cement, concrete, stucco and mortar. The NC designation means non-chloride, so it doesn’t attack (rust) metal. I’ve used galvanized stock panels to attach the burlapcrete to, and had been wanting to keep the breathability which might be lost with this type of waterproofing. The burlapcrete was a bit rough as a finish coating, so I’ve tried a variety of stucco treatments which all seem to work well. (And stucco is designed to be somewhat porous / breathable.)

  5. Sure would like the recipe for the “foamy” concrete.
    If it were me I would use rice hulls for insulation. Thermal mass is wonderful but the strength , and cost, of the necessary foundation is higher.
    Rice hulls weigh about 10lbs. per cubic foot and a cubic foot has an r-factor of a bit over 50 . It is is also much less labor to install , is varmint proof, fire proof, and packs very little.
    There is a method of using several layers of very taunt fiberglass window screen painted with a mixture of latex paint, waterproof carpenter’s glue and sand that supposedly last 20 years in very dry conditions. If that mixture would work on burlap it might be a cheaper alternative for interior walls and ceilings .

    1. Rice hulls sound like a decent insulator, I haven’t looked into it personally. As for the ‘necessary’ foundation having to be stronger and more costly dependent upon the addition of thermal mass, that’s if you’re building a concrete foundation. Straw bale and earth bag construction has often employed the rubble filled trench foundation, and my own earth bag structures have included the first several courses of bags being filled with gravel to reduce settling and erosion. Then I’ve backfilled the first few feet to raise the floors up out of any plausible flood zone. From 2006 to 2014 I haven’t noted any cracking of plaster or stucco related to settling.

      1. I wonder if the “foamy concrete” was similar to the foam or air entrained concrete used today, using a foaming agent (common dish soap has bee used with some success) Hmm, may have to experiment with that combination.

  6. Hi Annesley

    Great information mate.

    I found your blog above via a search about “cement hessian” that my Mum told me was used in the distant past here in Australia. Sounds like the same origin as the “petrified hessian” mentioned by Fran above.

    I am impressed by your testing process. I thought it might offer some modular flexibility if I were to create flat panel versions of this material, of full wall height, using a horizontal rubber or plastic mold to shape them into a consistent size with matching joint surfaces.

    Given the material’s apparent strength, if these molds were properly shaped with some depth, the resulting panels sound like they could perhaps be structurally sound without a steel or wood frame. When dry they could be stood up and bolted together in various floor plans.

    Your thoughts?

    Cheers

    Ian

  7. Try adding microsilica, also known as silica fume, to the cement mix about 10% to the cement. Then spray it on the wet burlap with a simple hopper sprayer typically used for “popcorn” ceilings. This method is less labor intensive and more controlable. Someone needs to constantly be supplying the hopper with fresh mix while you spray it. Holding more than 5 pounds of mix at a time in the sprayer will kill your arm after awhile. If you want to get real production going, use a peristaltic pump sprayer.

  8. This all looks so much like my mates mud brick house she made at Somerset Dam. She did it with all recycled stuff as well for doors and windows, and it is amazing. Would have been better if she had had some cash to throw at it too.

  9. I like your buildings. I’m interested in burlapcrete. Since you like steel structures, I wrote software which can make a steel space frame in any shape imaginable. The frames come with instructions on the bars and the system works like a techno barn raising. Large groups of volunteers can work in parallel. We use it like a 3D printer. Look us up and let’s chat. http://www.arcologynow.com

  10. Has anyone tried using polypropelene mesh or polypro earthbag fabric instead of burlap? We are building in an extremely humid environment (Yucatan) and worry about traditional burlap and mold. Our hope is to do a geodesic dome in burlapcrete or possibly ferrocement (or a mixture thereof).

  11. BTW to the Annesleys- thank you so much for this sharing this information! This is the best info I have found on the subject.

  12. Ever try magnesium phosphate cement? Michael Collins creates some really awesome stuff using burlap dipped in it or painting it on. you can find some info on greenbuilding.com about it.

  13. We now have a family discussion going on about doing this for additional chicken coops. The kids are designing/engineering away. Thanks so much for sharing all your hard work. All best to you!

    1. For garden walls I often use T posts about four feet apart, and a cattle panel (available at Tractor supply or Lowes at least around here) It’s like heavy fencing material, but more rigid. Attaching the cattle panel to the posts can be done with wire, and the panel is solid enough to hold up the burlapcrete. I actually tend to just go for making a ferrocement garden wall, same construction but instead of burlapcrete, overlapping stucco wire (basically same as chicken wire) in several layers, or metal lath for use with stucco. The metal lath is more difficult to attach and is very sharp, however. Once the wire is up I slather it with one part portland cement and two to three parts sand. Being odd, I tend to include some concrete bonder to give it a wee bit of elasticity. There are also additives such as Anti-Hydro which make concrete waterproof when mixed in. Those are good for outdoor walls, and I’ve used it to make waterproof concrete water storage tanks.

      1. Can one use burlapcrete to make a waterproof water storage tank if Anti-Hydro is mixed in?

  14. enjoyed reading this, am building a ferrocement house in the philippines , there the quality of life is hi dine the structure from the sun to avoid it becoming a heat sink

  15. I recommend this book from Australia for its coverage of the technique.

    The author also contends that the cheapest and best waterproofing agent it’s a slurry of pure concrete painted onto the surface.

    “Cement and concrete for the handyman : a complete work on all forms of concrete and cement work for home and farm /​ by “Domus”.”

    Also, Kurt Billigs method is covered in his book “the owner builder”.

    I’m rebuilding my library, and when I find the book I’ll post it’s title here: a guy building with concrete canvas and using strips of Hessian like bandages used in casts for broken bones, to join bamboo poles.

    A Very interesting technique

    I have yet to try the methods describes above.

    1. Interesting. I’d be a bit concerned about the pure cement being waterproof, as pure cement is hygroscopic aka water-absorbing, like a sponge. Water may not pass entirely through and leak to the inside, but the surface will be permeable to water, which if in a climate where it freezes would likely lead to the formation of cracks. Once painted I would suspect it would last fine as long as the roof coating paint was maintained. Perhaps there is a mystery of chemistry or physics that I’m missing… Not saying I completely understand the chemistry at play, I’m sure water runs off the surface but the surface would likely remain damp, as cement by definition is hygroscopic in nature.

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