Why
Building From the Inside Is Easier and Better Than Building From the Outside
by David B. South
 David B. South, President of the Monolithic Dome Institute |
The Monolithic Dome was developed to take advantage of building a structure from the inside. I used to tell people, "I am from Idaho, and nobody told me you had to put the roof on last. We establish the roofing membrane first, then insulate the building, and then put up the structure, working on the inside, out of the weather."
Obviously, it was an attempt at being funny, but it is undeniably true.
The Monolithic Dome is absolutely ideal to build. First thing up is an Airform (air structure) that protects the job site. Next, the Airform is urethane insulated on the inside. Sometimes this is tough if it's too cold, but usually there's a weather break that allows the first layer to be applied.
Once that first layer is applied, weather as a construction factor is eliminated. The rest of the insulation, the rebar hangers, and the rebar can be installed in the shirt-sleeve atmosphere of the Airform's interior.
Concrete (shotcrete) is the heart and soul of the completed building. It is sprayed in place. Believe it or not, it is much easier to do a good shotcrete job spraying overhead, instead of down. The major problem with shotcrete is rebound around the reinforcing.
Rebound is aggregate particles that separate from the air stream. These particles are not covered with enough cement paste to make good concrete, so they keep good concrete from embedding the rebar.
In other words, when spraying down, the rebound lays against the rebar. But when spraying overhead, it falls clear.
Too much water is concrete's worst enemy. It weakens the concrete and makes it crack more. Usually, concrete crews supply the concrete with too much water because that makes it easier to pour.
But with overhead spraying, the last thing you want is a too-wet concrete. It won't stick. Instead, the worker handling the nozzle ends up wearing it.
We know this so well, that we have to watch our crews to keep them from spraying shotcrete with too little water. Too little water makes fantastic concrete, but it prevents the shotcrete from wrapping around the rebar as it should.
Since your eyes and hands are on the top part of your body, you can see the application overhead better than if it were below your feet. You have more control than when spraying down. Using scaffolding when spraying overhead also makes the job easier.
Concrete sprayed on the exterior suffers from all the vagaries of weather. Since the concrete's surface dries quickly, cold joints present a real problem. It's tough to get wet concrete to bind to concrete surfaces that are already dry. Rebound creates a huge problem between layers. Concrete cannot be applied in rain or the threat of rain. Cold weather absolutely shuts down a shotcrete operation.
There simply is no way to multi layer a large dome with concrete on its exterior and match the integrity you get when spraying a Monolithic Dome on its interior.
Even if you must tent the truck, you can spray shotcrete inside the dome if it's below zero or raining. You are in control -- not the weather!
For small EcoShells, concrete on the exterior can make sense, especially if it's being hand-applied. This is really the only time building a thin shell concrete dome from the exterior might be more practical. If there are problems, small domes are more forgiving.
In general, construction from the inside is easier, faster and much simpler than from the outside.
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