Made with Xara Web Designer Dome construction begins with making a fabric form. This can be done by one of two methods. The first method is to sew together the polyester fabric and attach it to the plywood base or concrete footing. The fabric is then propped up and the urethane coating is sprayed into it with the inflater fan running. When the fabric becomes sufficiently sealed, the fabric form inflates. The second method is to pre coat the material before the gores are sewn together and seal the seams after inflation with urethane coating. We spray high density closed cell urethane foam on the inside of the fabric form after it is completely sealed with coating and cured out. We generally use 3# density foam that has a compressive strength of over 50 psi. We apply the urethane foam in passes up to 3/4 inches thick until we reach the designated thickness (usually 3 to 4 inches). After spraying in the foam, we lay out the openings, which is done in a variety of ways. In the downstairs of our own home we have many openings where we attached the rough frames to the dome shell (the foam surface). We attached them plumb and filled in the lacking areas with Styrofoam. We use the sprayed polyurethane foam to then tie it all together and attach it all the the foam insulated shell. Other large openings we simply outlined with strips of extruded Styrofoam, screwing them to the foam as a termination point until the molded foam overhangs could be attached and the re bar bent into them to tie them in structurally. Re bar hangars are put into the foam in horizontal lines according to engineering specs (usually 12 to 18 inches between lines) from the floor to the very top. The vertical re bar is attached to the horizontals so these hangars are the only ones needed. We spray in the first layer (1/2 to 3/4 inch) of concrete to hold in the re bar hangars. In large openings we may put some re bar into the first coat of concrete to help support the weight load that will be sprayed above it. When the first coat of concrete is sprayed all the way to the top and at least a day old, we are ready to tie in the re bar.  Engineering provides for extra re bar around openings, in the footing and any other special needs application. With the re bar tied in place, we begin to shotcrete with the footing. You’ll notice in the picture that the re bar (vertical) comes down into the footing and is bent horizontally. This allows us to spray in the footing and move right up the dome shell without lap joints. This also provides insulation against the footing without having to spray it in from the outside later. You don’t need any form boards for the footing as long as you’re spraying at a slump of 2 1/2 inches or drier (the drier the better). The rule of thumb is to spray the shotcrete as dry as you can pump it. With a good S- tube hydraulic concrete pump (the only kind I would recommend) I have pumped down to 0 inches of slump (I checked the slump when I was done spraying). We spray in the re bar in 1 pass under normal conditions and cross rake it when we are done to ensure a uniform surface. This process is an important preparation for the finish coat which will be troweled while very plastic and sponge floated to leave a very nice texture without any re bar lines. Some areas of the dome shell require extra thickness of concrete involving an extra pass or two. This includes  around doors, windows, and other openings. Ledges can also be formed onto the shell inside to set 2nd story floor joists on. Before we spray on the finish coat of concrete, we attach window overhangs, dormers, entryways etc. These units are urethane foam pieces cast in molds that we design for single or multiple uses. The final coat of concrete made of sand, cement and additive must blend together the interior surface into and attractive, textured finish.  The interior of the shell being finished, we move to the dome exterior. We apply multiple coats of urethane rubber coating with ceramic aggregate being blown into the first coat or two for texture. This application provides a more durable protection to the coated surface also. Building Process Click here to return to the top of the page The building process covered herein is only for built in place thin shelled concrete domes. Our transportable, light weight building process is similar. We will share pictures in the coming season. Where Portable and Permanent Meet