this method is, if the wall or foundation shifts in any way, it cracks and water is able to penetrate through it easily. Bituthene (registered name) is very similar to the three coat layering process only in one step. It comes already layered in sheets and has a self-adhesive backing. Applying it manually is the same as with the layering method, in addition, it is sun sensitive and must be covered very soon after application. Eco-Flex is an environmentally friendly waterproofing membrane that seems to work very well on foundations, but not much is known about its effectiveness in earth sheltering. It is among a group of liquid paint-on waterproofing products. The main challenge with these products are they must be carefully applied, making sure that every area is covered to the right thickness, and that every crack or gap is tightly sealed. Bentonite clay is an alternative that the most environmentally friendly. It is naturally occurring and self-healing. The drawback to this material is that it is very heavy, difficult for the owner/builder to install, and subject to termite damage. Bi-membranes have been used extensively throughout Australia where 2 membranes are paired together—typically 2 coats of water-based epoxy as a 'sealer' and stop the internal vapor pressure of the moist concrete exploding bubbles of vapor up underneath the membrane when exposed to hot sun. The bond strength of epoxy to concrete is stronger than the internal bond strength of concrete so the membranes won't 'blow' off the wall in the sun. Epoxies are very brittle so they are paired up with an overcoat of a high-build flexible water-based acrylic membrane in multiple coats of different colors to ensure film coverage—this is reinforced with non-woven polypropylene textile in corners and changes in direction. Insulation One or more layers of insulation board or foam are added on the outside of the waterproofing. If the insulation chosen is porous, a top layer of waterproofing is added. Unlike the conventional building, earth shelters require the insulation on the exterior of the building rather than inside the wall. One reason for this is that it provides protection for the waterproof membrane against freeze damage, another is that the earth shelter is able to better retain its desired temperature. There are two types of insulation used in earth shelter construction. The first is close-celled extruded polystyrene sheets. Two to three inches glued to the outside