Leaks from Boltholes

Leaks from boltholes occur on poured basement walls. They appear as water stains about 20 inches from the ceiling and floor, about every six feet, but not everywhere. Bolthole leaks can be repaired with tar and a cork.

The bolthole is from the wood forms used when the concrete basement walls were poured. Once the concrete hardened, the bolts were removed, and the forms were dismantled. Then one of the crew filled the holes with mortar or concrete and the exterior wall was waterproofed.

Years later, the waterproofing has succumbed to pressure and water is seeping in the bolthole. The best repair for bolthole leaks is to waterproof the wall on the outside, i.e. at the point of entry of the water. Always stop the leak at the source. I have been repairing this problem with a roofing tar cartridge in a caulking gun, a cork, and hydraulic cement.

The first step is to chip out the hole from inside the basement until you can get a measurement of the diameter of the hole. It is usually a 5/8- or 3/4-inch hole that will determine the cork size. The proper sized cork will fit tight in the hole. When you purchase the corks, acquire a 10-inch bolt or pipe that is a little smaller than the cork. It will be the pushrod used to drive the cork in the wall.

Install two or three pumps of tar deep in the hole. Then insert the cork and with a hammer and the pushrod, drive the cork and the tar deep into the hole. This will drive the tar to the outside wall and stop the water at the point of entry. Do not get overzealous pounding against the cork and force tar past the cork, and back towards you. This would get especially ugly if your face is close to the hole when the tar squirts out.

The tar and cork alone should waterproof the hole, but the hole can be filled with hydraulic cement for those that want to go the extra mile.