2Care must also be taken that holm timber be not used with oak; for as soon as oak becomes damp, it warps, and causes cracks in the pavement. If, however, holm is not to be had, and on that account it be absolutely necessary to use oak, it should be cut very thin, by which means its power will be diminished, and it will be more easily fastened with the nails. Then through the edges of the boards two nails are to be driven into every joist, so that no part of the edges may warp. I do not mention the chestnut, beech, or the farnus, because neither of them are durable. The floor being prepared, fern, if at hand, and if not, straw, is to be spread over it, so that the timber may not be injured by the lime.