Even with only one column inch of water column pressure (1/27th of a psi) you can put a concrete brick on the top of this polydome with minimal effect. The pressure easily supports the weight of fabric and cement paste. The same is true for large domes as well. It is truly amazing how little pressure is needed to support a substantial weight. The pressures are measured with a simple manometer, which you can build for practically nothing.
We have since abandoned this method of making a complete bubble for the form. Though it's used by Monolithic Domes and others, it's wasteful of materials and difficult to make into wide variety of shapes. Our new double layer forming method offers much more flexibility and is simpler.
Below is a bathroom vent fan encased in an enclosure made from "door skin" (1/8" plywood). The hose is sump pump hose (washer drain hose) and is attached to a PVC pipe taped to the polydome skin.
This hexagonal model was our first one to be made with the bubble form method. The outer arch forms can be seen still attached to the arches. They were later removed. This dome was made of plaster with lightweight cotton scrim reinforcement. It didn't last very long in the elements, but was a great study. It had a very thin shell and was fragile to move around. Later we made a concrete square dome that is quite substantial. You can sit or stand on it. Both are shown below.
Models provide an opportunity to learn about arch design, inflatable form design, materials and the relative size relationships between all the design elements.
Notice the burlap patches used to form the structure of the square dome.
This dome is about the size of a small playhouse. It uses our new double ply sectional inflation system. Burlap is laid over the inflated form and cement slurry is coated over the burlap to make half the dome. The form is turned 90 degrees, and the process is repeated for the second pair of arches. In the last photo, a second coat of lightweight perlite/cement mix gives greater substance to the dome.