A Looking at the foundation from the inside you will be able to tell. Poured concrete foundations found in newer homes are solid concrete and look similar to the floor. Block foundations are concrete blocks that measure 16” long by 8” high and vary in depth, usually 8” or 10”. The blocks are joined together using mortar to build the wall. Stone foundations are found in century homes and very old building. Stone foundations are made from various sized field stones held in place with mortar.