Light Weight Concrete Roofs
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Light weight concrete roof vaults are strong, comfortable, durable, easy to construct and maintain, attractive, and inexpensive.Concrete is strong in compression so concrete roofs are ideally built in shapes that are strong in compression; shells, domes, or vaults. In my opinion, flat concrete roofs do not represent good thinking. The only way to make flat roofs strong enough to support themselves, and the loads they will carry, is to use a LOT of metal reinforcing and hard, structural concrete. Even at that, they are prone to failure. There were some very ugly pancakes of flat concrete roofs and floors after the last big earthquake in Mexico D.F. Vaulted roofs have much less tendency to collapse in this manner.

Light weight concrete vaults are easier to build and maintain and can be build with a fraction of the metal reinforcing needed in flat concrete roofs.

Rooms with vaulted ceilings have a great feel in the lived-in space. This is especially evident in low income / cost dwellings. Ceilings seem higher than they actually are and everything feels more spacious.

Lightweight aggregate roofs are good insulators and the thickness can vary according to the climate. Three to four inch ( 8-10 cm) roofs are about right for the mountains in Mexico to give you "warm in the winter and cool in the summer".

Sealing: Here in Mexico, we've been sealing roofs with polished, fibered mortar. They are then, usually painted later with latex roof paint. In harsher climates one has to resort to more exotic membranes.

Patching: We have had excellent success patching these roofs and patches almost always "take". Simply chisel out the offending crack with a wood chisel, wash out the crack, paint on a cement slurry to bond, and then polish with fibered masonry.

A well-built and maintained concrete roof should last at least 200 years.

mxSteve at gmail dot com
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