Working around the antique fieldstone foundation, Kevin and Norm find Tom and mason Mark McCullough replacing the inadequate foundation under the addition and pouring a new slab in the basement with a concrete curb to bolster the walls. Breaking through the living room ceiling, they discover a lot more headroom, along with the original plaster molding and medallion, almost completely intact. In the second half of the hour, on ASK THIS OLD HOUSE, Tom heads to Seattle to install crown molding. Roger replaces a rotted fence post. Kevin explains the difference between cement, concrete and mortar. And the guys ask, "What is it?"