The concrete house, especially that built of blocks, often has the defect of being damp on the interior, unless precautions have been taken to avoid this. It is always best to fur the interior of walls, although there have been cases where the blocks have been waterproofed and the interiors remained dry. Usually those blocks which are cast in a very dry state are porous, while those which are poured show considerable compactness. The great difficulty in using concrete blocks lies in the inexperienced and inartistic work of the large number of "would-be manufacturers," whose only claim to the product consists of having purchased a machine which will turn out so many blocks a day and reap them an advertised fortune in a short period. A thoroughly reliable concrete block can be made, if there is used plenty of good cement, clean aggregate with proper proportions of fine and coarse to secure density, sufficient water to make a wet mixture, and then the product kept damp while curing. The surface should also be finished in some artistic manner. A good method consists in applying about an inch of white cement and showy aggregate to the outer facing of the block, and then, when the block has been set into the wall, finish it off with a stone-tooling machine, such as a pointer, operated by a pneumatic hammer. Blocks, also, should be of the hollow-wall type, so that an air space between can be secured for ventilation and insulation.