Can you suggest repairs in a basement that is damp and is flooded during heavy rains?
Local conditions will determine the necessary repair work. Poor concrete in walls may permit seepage or cracks in the floor slab and may indicate structural inadequacy to withstand water pressure. Before beginning repair work, check the drainage system and construction of gutters. Proper location of downspouts to carry the water away from the walls may help. The ground outside the basement walls should slope away from the building. If drainage is found to function satisfactorily and is not at fault, the walls may need repair. This repair work should be done from the outside when the water table is above floor level, and can be done satisfactorily from the inside in case of moisture seepage. Cracks in the wall should be cut back to form a V-shaped groove and filled with a 1:1 1/2 cement-sand mortar of damp consistency. The mortar is to be rammed into the crack with a caulking tool. Two 3/8-inch-thick coats of 1:2 cement-sand stucco are to be applied, following established stucco practice. Seepage may occur through cracks at the joint between walls and floor. If this is the case, cut out cracks to a depth of about 2 inches, forming a narrow groove and fill the space with hot tar or a mixture of tar and sand. General cracking of floor or porous concrete may require placing of a new floor over the old one with tarred joints at the walls. When the floor is cracked due to water pressure, a new floor must be laid. The thickness depends on the upward pressure that must be overcome. Figure 62.5 pounds per square foot upward pressure per foot of water above base of floor. Each inch of concrete weighs about 12.3 pounds per square foot. For a 2-foot head of water, you must overcome an upward pressure of 125 pounds per square foot. A total floor thickness of 10 inches should be sufficient. When pressure has cracked the floors, it is advisable to provide a membrane waterproofing of two or three layers of burlap mopped with hot tar or asphalt placed between old and new floor. This membrane should extend 1 foot or more up the side of the walls. Plastering or painting should be carried down over the membrane to the floor.