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Latex, or acrylic, concrete is an underused and little known form of concrete for the DIYer, which is a huge shame. It has so many benefits, especially as a roof (or unique art project). It is:
  • Lightweight - the support structure does not need to be as extensive as with other materials.
  • Fast Setting - you don't have to be as scared of clouds on the horizon as with concrete.
  • Goes Quick -  almost equals the speed of putting up metal roofing, which is a material we often avoid as it does not last as long, or look or sound (in rain) as nice as concrete options.
  • Inexpensive - for its strength, durability and speed, it is cheap.
  • Artistic - it allows for many different designs, though a pyramid structure seems to be the most efficient.
We’ve used latex concrete for the roof of our cisterns (see steps 8 and 9 of How to Make a 6000 Gallon Water Tank), as well as the roof of the kids’ bedrooms. It would also be ideal as a quick and exceptional-looking porch. 

The shape and style of your latex concrete project depends almost entirely on your imagination. Within this article, we’ll run you through both the overall principals and the more specific details, and we hope you go on to make some wild looking creations.

For more information on concrete or other building materials, visit the shelter section of our site.

For more information about this method of building, please read "Latex Concrete Habitat" by Knott and Nez

Step 1: Materials and Tools

For the posts:
  • Metal reinforcement (rebar or castillos)
  • Cement
  • Sand
  • Vinyl or plastic
  • Lumber, to hold the form together and in place
[Tools: concrete mixing equipment, like shovel and wheelbarrow or mixer. Cans or something to pick up and pour the concrete. A trowel. Tape measure.]

The Frame:
  • Either metal, lumber or rebar-reinforced PVC
  • Screws or wire to assemble the frame
[Tools: Drill, staple gun or pliers. Saw. Tape measure and marker.]

Fabric:
  • Vinyl tarp or billboard (optional)
  • Loose-weave fabric, like nylon netting or shade cloth
  • Either screws and washers, staples or tie-wire (to attach the fabric)
[Drill, staple gun or pliers. Tape measure, pen and scissors.]

Latex Concrete:
  • Acrylic Latex (100% acrylic concrete bonding agent)
  • Cement
  • Fine screened sand
  • Paint
[Bucket. Drill with mixing attachment (or stick and some muscle). Long handled brushes. Cans or small buckets to pour with.]

Step 2: Posts

In the case of a porch - or even a roof that you want to make before doing the walls (for example, if you want to start catching rain water to use for the rest of construction) - you will need to make posts for the structure to rest on. And concrete posts are a strong, durable option.

We have found that fabric forming is one of the easiest and cheapest ways to form concrete. Instead of time consuming and costly wooden or metal forms, you use little more than a piece of plastic or similar fabric. The end result is not only aesthetically beautiful, it is also stronger, because it lends itself to rounded shapes, compacted pours, and consistent curing.

We have more information on how to make a fabric formed post here, so please consult that Instructable for more details. However, we wanted to give you a rough outline of the process within this article.
  1. Mark out the corners of your structure. To make sure it’s square (if you want it to be), measure diagonally between each corner. The two lines of the figurative X are be identical when square.
  2. At each corner, dig a 12” diameter hole, about 2 ft deep (and preferably wider at the bottom than at the top, so that it is “belled”).
  3. Stand metal reinforcement up in the hole. Make sure the bottom of the metal is up on rock or plastic instead of touching the dirt. Make sure the post is plumb/level.
  4. Pour concrete in the base, to just above dirt level. Wait a couple of days before continuing, so that the concrete can set.
  5. Cut a length of vinyl tarp or black plastic, 36 inches wide. It needs to be a little shorter than the metal reinforcement, as you will be tying the roof’s frame to the reinforcement. For ease of explanation, let’s call the post 96” tall (the reinforcement will have 2 ft extra in the ground and 4” extra on top, so will be 124”).
  6. Place two pieces of  8 feet 1x4s, 22 inches apart (the tarp will stretch a little, so make it a little skinnier than you want the post to end up). 
  7. There should be about an extra 7” of tarp on both sides. Double this back on itself and staple it well to the lumber.
  8. Stand the form up and put it around the metal reinforcement of your post, so that the two 1x4s meet, flat against each other. Screw them together.
  9. Level the boards in two different plains, and then brace the form using lumber or metal.
  10. Pour concrete into the plastic, patting it as you go. You want the concrete a little soupy, so that it fills the form better. However, remember that the drier concrete is, the stronger it will turn out, so do not make it soupier than necessary. Patting helps to compact the concrete and release air bubbles that can make the post weaker. If you pat it too much, the post will start to bulge at that point.
  11. When the concrete is hard to the touch, take down the braces and then release the screws and carefully peel off the form, which you can store for reuse. We have found that concrete sets up far quicker in a plastic form – we don't really know why.

Step 3: Frame

The purpose of the frame is to create whatever shape you want your roof to be. It only needs to be strong enough to hold the fabric in place until the latex concrete hardens. We have tried three different materials for the frame, each with their advantages and disadvantages.
  1. Metal is the strongest and most durable. It is also lighter than wood, as you would not need a very thick gauge metal. However, it is expensive and requires better tools (saw blades, drill bits and, even better, a welder). You will also have to use screws and washers to attach the fabric.
  2. Lumber is fairly cheap, and easy to work with (if you need an explanation for that last statement, go and cut a piece of metal and lumber by hand, and see what you think). You can also staple the fabric to the wood, which will save time. However, it’s kind of heavy and will not last as long, especially in damp conditions.
  3. For the roof of our water tanks, we use 3/4” PVC with 1/2” rebar inside. It worked great. It’s cheap, light and easy to work with. However, it’s not as durable and we wouldn’t want to walk on it. It’s a good choice for a small roof that you won’t need to get on, and that you want to be curved (arch or dome).
No matter which material you choose, you will want to have a base frame. This consists of a box or circle that is attached to the posts or wall. From this will rise your peaks or arches or whatever. 

This form of construction lends itself to sweeping shapes, which are often very difficult to visualize in your head. Our strongest recommendation with latex concrete is to buy yourself a box of straws and some plastic wrap or flimsy fabric. Pick a scale for your straws and make a base frame that will fit your particular project’s dimensions. Then play with various shapes and possibilities by using the straws as your frame material and the plastic wrap as your fabric. 

You can make any shape you wish, so long as it is structurally sound. While the tank roofs we do are dome-like, set on circular walls, the kids’ room roof consists of three circus tent style peaks. You can similarly use peeks, or arches or conics. You can also stick pipes up into the fabric from below to make extra dips or features. You can remove these once the latex concrete has hardened. 

Step 4: Fabric

You want to use a fabric with a fairly loose weave, so that the concrete can fully penetrate it. Some people use burlap and are very happy with it. At first, we used two layers of fiberglass screen, alternating the direction of the fabric for each layer. As it turned out, this was a tighter weave than what you really want. However, it still worked just fine, just took a little more work to get the concrete to soak through properly. We’ve also used orchard netting, doubled up.  80% Shade cloth works well. The key is finding something cheap and available in your area, and then doing a couple of test runs, to make sure it will work. The thing to look out for is penetration: you want a coat from the top to penetrate all the way through the fabric without falling right on through.

Something we have started doing, which we would highly recommend, is putting a vinyl tarp on top of the frame, and then the fabric. Not only does this make less mess when applying the latex concrete, it also provides a waterproofing backup, should a hairline crack appear. It does decrease the sweeps you might achieve with a more flowing fabric, but you can always drape it a little if you wish.

Once you’ve decided on your fabric, attach it to your frame. Depending on the frame’s material, you can use screws with washers, staples or tie it on with zip-ties or wire. 

The beauty of this system is that any hole and extra bit you want to cover, just attach fabric over it. It is a forgiving style of building and allows for some last minute whims.

Step 5: Latex Concrete

Once all your fabric is firmly attached and you have added any extra features by pushing out the fabric with poles from the underneath, you are ready to do the latex concrete.

So, where do you get the latex, or acrylic, from? We started off using a product called Sikalatex, but we ran out and had to move on to a 100% acrylic concrete bonding agent, which was much better. Look for anything with a high percentage acrylic. If it stinks of ammonia, you’ve got the good stuff, but most acrylic additives for concrete will work.

You want to do a minimum of three coats: a scratch, brown and finish coat. You can do more coats if you wish, but three is sufficient for most applications. To mix the concrete, we used a five gallon bucket and a drill with a paint stirrer on it. The concrete is fairly liquid, and thus easy to mix, no matter how you do it. It does dry pretty quickly, due to the latex, so don’t mix huge batches unless you have the manpower to apply it (which is also very fast).

The application is super easy. You can pour (or throw) it on and then spread it out using a paint or broom-like brush. It sets up fast, so you can usually do a couple of coats in a day. After a couple of coats it starts to gets hard. That hardness will increase over time, as it cures completely. In fact, it will continue to get harder over weeks. Even though you probably could, strength-wise, we recommend you don’t put your weight on an unsupported part of the fabric until it is fully cured.

Scratch Coat
First you do a coat on both sides of the fabric. If you have a vinyl tarp between the frame and the fabric, you won’t need to coat the underside, which is great as that’s the hardest part. Just make sure that the whole fabric gets covered (you can pick up pieces of the fabric and then let it snap back onto the tarp with concrete underneath. 

The mix we used for the first layer was a 1:1 of water and acrylic, and then mix in your portland cement.  It should have the consistency of heavy cream. The mix wants to be pretty liquid for this first coat, so that it penetrates (but doesn’t fall through) the fabric.

Brown Coat
The subsequent layer consists of a 1:1 acrylic and water, and then add 1:1 cement and finely screened sand.  This mix can be more liquid than the first, as it will set fast.

Finish Coat
Do the final coat without sand. It will have a much smoother finish and not use as much paint.  You can make this mix very liquid and paint in on thinner than the previous coat.

When we did the kids’ rooms roof (a 30 ft by 15 ft structure), we left three holes in our structure, one at the top of each peak, so that we could get up there and pour the next coats easier. We then went back and covered those holes before putting on the final coat. Latex concrete binds very well to itself, so you do not have to worry about cold joints, as with regular concrete.

You can, after the concrete has cured a couple of days, paint the roof.
This is great. Is this something that has been used for years or is this something you came up with yourself? <br>I'm wondering if this roof will last as long as a regular shingle or metal roof also. I have a few question on this. <br>How many Acrylic Latex gallon bottle did you actually used on the 30 x 15 roof of the kids room? Also I have a large 30' x 24' shed that I'm turning into a garage/workshop and it has metal roofing at this time that is starting to rust and I was thinking of painting, do you think it would be a great idea to do this on this roof and if so should I do it (add the cement) on the existing metal roof on the bare metal itself or add maybe billboard material before adding the cement? Thanks for the Instructable.
Dr. George Nez and Dr. Albert Knott developed this technique for low-cost roofing in Africa. They have a book, which I highly recommend, called &quot;Latex Concrete Habitat&quot; (there's a link to it in the introduction above). <br> <br>We used 4 x 5 gallon buckets of acrylic on the kids rooms (33 ft by 12 ft), so 20 gallons. <br> <br>To add to metal, I would lay down a vapor barrier (black plastic), then netting and the concrete. I don't know what your structure underneath is, but make sure it can hold the weight, first.
<p>Hey I was wondering on how the roof been holding up after these few years, any update?. Have you had any problems with it or have you had to do any maintenance to it, any cracks? I'm still interested in this idea to replace my roof at the shed and was wondering if you would have done anything different if there was another one built. Thanks</p>
Great job with this Instructable! This is fascinating. I haven't seen any how-to on this type of construction before. I'm envisioning many different ideas where I would like to try this. Also, very helpful comments. Thanks!
Could this be applied using a stucco/plaster sprayer? It seems like spraying would be easier &amp; quicker than brushing/brooming it on, and would also allow for a more even layer on each coat.
At first, spraying looks like it would be easier, but the distances involved are bigger than you think, so you would have to work out a scaffolding system to get the sprayer closer to the roof. The nice thing about the broom method is you can dump a lot of material on the roof all at once, and then spread it out. It goes fast.
Cool technique, would you say that a latex concrete roof is walkable? What if it's fully supported by say plywood underneath? I've been trying to make a walkable roof for the last year and so far epoxy hasn't worked and regular roof coatings are not up to being walked on. In my case, I'd be just going over my existing epoxied roof which is mostly waterproof but started to photo and or heat degrade so the concrete would really just be a coating. <br> <br>So in the scratch coat is 50/50 water/acrylic and just portland? How much portland per gallon (or 5 gal) of liquid? <br> <br>Again, the brown coat has the same liquid proportions but how much of the sand/portland mix per gal of liquid. <br> <br>For the finish coat, you mix paint into the cement or are you saying that that you won't use as much of the concrete mixture? Is the finish coat material more or less the same as the scratch coat?
It is walkable, though we tend to stay to the parts that have structure underneath. I would not want to walk on it regularly. With plywood underneath, it could be done. <br> <br>The ratio of portland in the scratch mix depends on your situation, and the moisture content of your portland and/or sand mix. For each gallons of liquid, you'll need at least another gallon of dry mix, maybe a bit more. <br> <br>The finish coat is the same mix as the scratch coat, but you can make it a bit more liquid, and then paint it on thinner than the other coats.
<p>Just Curious if the addition of Chicken Wire, Aluminum or other type Window Screen material after the first coating, would be useful to add strength to a roof like this? (Sorry - Used to working with 1&quot; &amp; 3/4&quot; re-bar in meshes strong enough we can stand on them - going up in Retaining Walls for the Railway Banks. Just use to heavy built stuff with thinnest part at the wall tops of 2 feet wide.)</p>
<p>Hi, </p><p>I have a flat roof on a three story builing here in Montreal and want to re3plce the tar roof with concrete</p><p>Is this possible. Thank you</p>
<p>I'd like to know if I could apply this directly over a 20 year old asphalt shingle roof that has started to leak. Would I still need the nylon tarp/underlay and or the loose weave netting?</p><p>Also, have you worked out a cost per sq. ft or cost per 100 sq. ft, not including the tarp and netting?</p><p> If I need the tarp I'd probably go with a recycled 20'X35' billboard vinyl material and for the netting I'd use recycled construction site netting, the kind you see temporarily wrapped around hi-rises as they go up.</p>
We use billboard vinyl and shade cloth, and it works well, with just one layer of netting.<br><br>For covering shingles, I'd put down billboard vinyl and a mesh, and then paint 2-3 of the latex cement.<br><br>Cost depends on local materials, it comes out about 3/8&quot; thick.
<p>Can you give me an idea of how much your cost per sq. ft was? Would the shade cloth as used on hi-rise construction sites work as the mesh you are referring to, or what type of mesh do you reccomend? When you say it comes out to about 3/8&quot; thick, that includes 3 coats, each including sand, portland cement and latex, correct? How many gallons of Latex additive did you use in total on the 3 coats of 30x15 roof, how many bags of sand, and how many bags of portland cement? If I'm laying on 3/8 of an inch in total, that's likely close to two complete courses of asphalt roof, which would be a lot of weight, so I might have to strip the original asphalt roof first. Your comments?</p>
<p>Our cost was about $1/sf, but it depends on your local cost of materials.<br><br>I am not familiar with the high rise mesh you are talking about. We recommend shade cloth.</p><p>3/8&quot; total thickness.</p><p>I don't know the exact figures for materials, but I think we used 4 buckets of latex for that area. Total cubic feet of material for that space is about 12.5 ft3.</p>
Could you use this same technique to build a wall? What i mean is say i wanna build a small storm shelter, would this be water proof, and would the cement adhere to the fabric corectly in a vertical position, and if so is there any risk of gasification from the cement?
<p>It can be used as a stucco for a wall, but not by itself, it isn't strong enough. Here's a simple wall method that could then be covered with Latex Concrete: </p><p>http://velacreations.com/howto/rapidobe-walls/</p>
Would this be a feasible roofing option for going over a double wide trailer homes existing roof? Possibly with high density foam insulation underneath it? Location would be north Texas so snow isnt a huge question though hail does come along every spring. I have been looking for a low cost durable roof option that I could do myself with a bit of help from the kids and this looks too good to be true. any info you could share would be greatly appreciated. grunefireheart@Gmail.com
<p>I tried this on a one man build bush pole shed. I went to the local dump / tip and asked if I could have old paint that was kept out of the normal rubbish for enviro reasons. I used old acrylic paint - water based stuff. I used shadecloth - which was the most affordable stuff I could find. I made the mistake of a too low pitch on the roof but I must say the task was manageable and the result fantastic. Actually it rained that night. Water actually pooled on the roof in a couple of places and I had to slide extra poles under the still flexible cloth to get rid of the puddles. I also used it on walls - both in and outside - with light straw clay slip as insulation between. Truly this is a very useful technique. Dont try to mix by hand - it killed my shoulder!!! Small batches with a drill stirrer. </p>
I mean do you think the stress load would be too much under a foot of snow? Would it hold up?
From what I've read on another site, they built a hypar roof test structure in Boulder CO in 1996, with 3'+ snow and it's still standing.
I think it would hold just fine, as long as your supporting frame can handle the weight.
<p>How would this type of roof hold up to negative degree temps. I live in Montana and it gets very cold up here.</p>
<p>I live in Montana and wonder if it would hold up to the weather here. It isn't the snow I worry so much about but the negative degree temperatures. It looks like it would be a great roof otherwise for the craft shed I want to build. I am slowly trying to work away from the grid.</p>
That almost seems too simple? <br>Garden shed needs a new roof, may be ideal for practice. <br>Lifespan should be much higher than sheet metal or wood/tar shingle or even plastic as that tends to crumble with UV exposure <br> Could latex paint be mixed with final coat to have it self coloured?
Just wanted to say congratulations on being a finalists in the Concrete &amp; Casting Contest! This was a fantastic instructable! Good luck!
Thanks a lot. There weren't that many entries in this competition, but it seems like the quality of all of them was excellent.
Really love this technique, I can think of lots of sculpture and design applications!! Thanks. I wonder if there are material data specs available for all those New England people wanting to know about snow loads!!
MgO is a far superior product to portland with additives for this and any other type of art or construction project. <br>https://www.instructables.com/community/Ever-heard-of-Ceramicrete-MgO-cement-Magnesium-c/
Thanks for this terrific instructable. What about using this technique to make large panels or tiles that could be overlapped on a roof structure such as trusses? Any thoughts?
you would probably need more reinforcement for that, and they would have to be a bit thicker. But, it could be done. Do some research into microconcrete tiles, it's similar to what you are talking about.
That wouldn't fly here in New England. <br>We get lots of storms and snow depth. <br>Plus building codes.
our storms are significant with 50 mph winds on a regular basis. <br> <br>As far as snow is concerned, it will hold up, as long as the structure beneath the concrete is able to hold the weight.
acrylic what ?Acrylic may refer to: <br> <br>Chemicals and materials <br> <br>Chemical compounds that contain the acryloyl group derived from acrylic acid <br>Acrylic fiber, a synthetic fiber of polyacrylonitrile <br>Acrylic glass, a term for poly(methyl methacrylate) (PMMA) <br>Acrylic paint, fast-drying paint containing pigment suspended in an acrylic polymer emulsion. It is a common medium used in modern fine art/art <br>Acrylate polymers, a group of polymers (plastics), noted for transparency and elasticity <br>Acrylic resin, any of a group of related polymers formed from a mixture of monomers selected from the C1 to C8 acrylate esters, methyl methacrylate and, often, styrene <br>Other
Acrylic concrete additive
Love the idea of this. I'm looking to create a central entertainment area in a social project and this could well be a roof system that would work.
Your concrete goes off quicker in a plastic form because it is non-porous and retains water better than wooden forms. Concrete curing is not a drying out process but actually a reaction with water so keeping the concrete moist allows it to cure quicker. <br> <br>You may have seen big construction projects 'ponding' large slabs of concrete by using a raised form and filling the top with water, this is to aid curing through the full depth of thick slabs such as are used for foundations.
How does it hold up to New England snow?
I have no idea, we've never built one in New England.
Great instructable! Love to see concrete work that's outside the box and showcases what concrete is capable of.
Wow! This is an amazing 'able. I've been wanting to try some of this kinda thing for a while. Think I'll give it a shot. <br>
Has anyone ever worked with MgO cement? MgO replaces the Ca found in portland cement. MgO cement makes a concrete that will incorporate cellulose and other organics into the crystalline structure. absorbs CO2 instead of generating it, is an order of magnitude stronger than portland, does not require wetting, and cures in minutes. So basically, you can take some burlap or old blanket and paint this stuff on, then fill the void with straw and cement so you can make super strong, light and thin structures. <br>I have looked for it locally but it does not seem to be in available to consumers in the US, probably because of the lack of sheep crap which is the typical source of Mg. It is amazing stuff. <br>http://greenhomebuilding.com/articles/ceramicrete.htm
That is very interesting. There are a whole range of cements/geopolymers. <br> <br>Is MgO cement something we could make at home?
Awesome..very practical.Has any form of of this been used in boat building, bridges or piers or any underwater structures? Thanks
The closest in boats are ferrocement boats which according to wiki was first known about in 1848 France
not that I know of, but possibly.
This was enlightening thank you!
This is pretty cool! I'm curious if anyone has experimented with paper concrete and acrylic.
The roof on my house now is shingled, I was planning on adding a metal roof on top but if this is a better option and more cost effective I'd like to go this route
This looks fantastic! <br>I'm just wondering: how durable is this? What happens during a storm? Does the concrete become brittle?
the concrete remains somewhat flexible, due to the acrylic content. This roof has survived a number of storms and winds in excess of 50 mph without issue.

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