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:
Metal, lumber, rebar reinforced PVC or cables
Screws or wire
Vinyl tarp or billboard
Loose weave fabric like orchard netting or burlap
Screws, staples or tie-wire
Acrylic (like 100% acrylic bonding concrete)
Fine screened sand
Tape measure and marker
Mixing attachment for drill
Long handled brushes
Cans or small buckets to pour mixture
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.
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.
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.
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).
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.
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).
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.