When this type of walling is used in cellars and basements, where it is often in contact with the ground, the external face of the wall is usually treated with several coats of a tar or bitumen substance, with or without felt, to resist dampness.是什么意思 When this type of walling is used in cellars and basements, where it is often in contact with the ground, the external face of the wall is usually treated with several coats of a tar or bitumen substance, with or without felt, to resist dampness.怎么读