If a concrete floor is placed at an elevation where any of the ground around it is within six inches of the floor surface or above it, block is the most common choice. If block must be used, the next consideration is how to seal block that is below grade. It is a common practice to coat the exterior of the block with foundation coating (tar) only. The problem with this approach is that the block acts like a sponge and draws the liquid into the block which dries the surface and degrades the protection. Economy Garages coats the sub-grade block with a cementitious coating that densifies the surface of the block, then coats it with fibered foundation coating.