Latex Concrete Roof

Latex concrete lends itself to unique and sweeping shapes that you couldn't achieve with many materials.

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A latex concrete roof is almost more of an art project than a roof. The shape and style of it depends almost entirely on your imagination. If you want to create something truly unique, this is the method for you.

Its advantages are that:

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 equally the speed of putting up metal roofing, which is a material we do not want to use 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.

Materials & Tools

Materials

Frame:

Metal, lumber, rebar reinforced PVC or cables

Screws or wire

Fabric

Vinyl tarp or billboard

Loose weave fabric like orchard netting or burlap

Screws, staples or tie-wire

Latex concrete

Acrylic (like 100% acrylic bonding concrete)

Cement

Fine screened sand

Paint

Tools

Drill

Staple gun

Tape measure and marker

Pliers

Scissors

Mixing attachment for drill

Bucket

Long handled brushes

Cans or small buckets to pour mixture

Step 1: Framing

The roof frame wants to be supported by posts or walls. Make sure that the support has something exposed to which you can attach your roof frame.

The purpose of the frame is to create whatever shape you want your roof to be. You can use either wood or metal. Wood has the advantage of being able to staple the fabric to it. The frame needs to hold the fabric in place until the latex concrete hardens. We have tried four different frame materials, each with their advantages and disadvantages.

Metal

This is the strongest and most durable material. 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, welder). You will also have to use screws and washers to attach the fabric.

Wood

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 of 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.

PVC

For the roof of our water tanks, we use 1/2” PVC with 3/8” rebar inside. It worked great. It’s cheap, light and easy to work with. However, it’s not that 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).

Cables

For one tank, we put up a PVC upright pole in the center and then had cables from it to the walls. It was very cheap and easy, but, again, not for walking on.

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 conicals. 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 2: Fabric

On our first attempt, we used two layers of fiberglass screen, stapled directly to the frame. We alternated the direction of the fabric for each layer and then applied the concrete mix. As it turned out, this was a tighter weave than what you really want. It still worked fine, just took a little more work to get the concrete to soak through properly.

Since using latex concrete for the roofs of the cisterns we build, we have discovered a much better technique. This is what we’ll describe, as it include a vapor barrier for your insulation underneath, and is a lot less messy (nothing falls through to the ground underneath).

Attach a vinyl tarp to the frame around the base of the roof. You can get cheap or free tarps from old billboard signs.
Put a couple of layers of orchard netting on top of the tarp and secure it around the base. You can also put some screws with washers to other parts of the frame.
Make sure the whole thing is taut.
It should all slope from the peaks down to the base of the roof (where you would put gutters). If you see any dips in the fabric, where water might pool, put a pole from the inside to push it out.

Step 3: Latex Concrete

First coat

In a bucket mix 1 part acrylic to 1 part water.
Add portland cement until it has the consistency of heavy cream.
Mix thoroughly with a drill and mixing ladle.
Pour this mix onto your fabric and spread it out. The orchard netting will not be covered, but it should have concrete all over it, in all its holes.

Second coat

When the first layer is firm, you can begin on the second. It usually sets up very fast, and the part where you began is sometimes dry by the time you finish (depending on the size of the roof).
Mix 1:1 acrylic and water with 1:1 cement and fine sand.
Pour this mix onto the roof and spread it our with brushes on handles.
You can do two layers of this mix if you wish. For tank and shed roofs, only one is necessary, but for a house, an extra isn’t a bad idea.

Final coat

Use the same mix as the first coat for the final one.
Smooth the coat using brushes.

Paint

Paint with a waterproofing paint once the concrete seems hard and dry. It will continue to cure and harden over weeks, but the paint will not interfere with this.
You can then add a colored paint if you wish. Roofs should be pale if you live in areas that experience high heat. White helps reflect the heat.

We left three holes in our structure, at the tops of the peaks, so that we could 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 concrete.

People spend a lot of time wondering what material to do walls out of, but walls are the easy part. It is the roof that is most expensive and hardest to do. We have a few more techniques we want to try out before deciding on our preferred roof system, but this is one we will almost certainly come back to.