When this has hardened sufficiently to admit of their erection, thin frames of metal are erected, enclosing the spaces to be occupied by the several outer and interior walls.
These spaces are filled with the concrete at a temperature of about 80 deg.

C.The tracery and the bas-reliefs impressed on the walls are obtained by means of patterns embossed or marked upon thinner sheets placed inside the metallic frames.

The hardening is effected partly by sudden cooling, partly by the application of electricity under great hydraulic pressure.

The flat roof is constructed in the same manner, the whole mass, when the fluid concrete is solidified, being simply one continuous stone, as hard and cohesive as granite.

Where a flat roof would be liable to give way or break from its own weight, the arch or dome is employed to give the required strength, and consequently all the largest Martial buildings are constructed in the form of vaults or domes.