DIY: How to Waterproof & Insulate Exterior Basement Walls

Wash the basement walls with a power washer and allow them to dry.

Examine the walls and locate cracks. Chisel away at the area around each crack, going deep enough so you reach the concrete beneath the bottom edge of the crack. Fill the crack with patching compound, smooth the surface with a putty knife and allow the patching compound to dry.

Examine the base of the wall where it meets the floor. If there's a gap between the wall and floor, fill it. Apply a thick bead of urethane caulk to the crack if it's a 1/4 inch or less in width. Fill larger cracks with foam backer rod, then apply the caulk over the backer rod. Smooth the surface of the caulk after you apply it.

Apply a waterproofing agent to the walls with a paint brush. Cover one block at a time, and work the brush in every direction to fill each nook and crevice. Allow the first coat to dry, then apply a second coat and allow it to dry.

Measure the walls and cut the foam insulation boards with a utility knife to fit your needs.

Place foam adhesive on the back of the boards with a paint brush and press them against the walls. Install the boards along the bottom of the walls first, then install another row on top of them, if it's needed. Stagger the foam boards in each row, just as you would stagger the bricks in a wall.

Cover the joints between the adjoining panels with installation tape to seal them.