In gauging up concrete, burnt ballast, with or without clean brick rubbish, will make fair common lime concrete, but for good concrete there should be no burnt ballast, and the brick rubbish should be clean and hard. For cement concrete, stone ballast and hard bricks, broken to pass a 2 1/2 in. ring, would be suitable. One of lime to five of the other materials, or one of cement to seven of the other materials, is an economical proportion. Burnt ballast, like a common place-brick, crumbles on exposure to the weather, and in damp foundations will in course of time go the same way; even in dry foundations it will not bear a heavy load.