Plug Holes and Cracks in the Foundation
Holes and cracks in your foundation can let moisture and water seep into your basement. Plugging them probably won't solve basement leaks, but it'll help. Hydraulic cement works great for patching holes in a foundation because it can set up even under water, and it expands as it sets to seal the hole and lock the plug in place. Use a cold chisel or an angle grinder fitted with a masonry-cutting disc or diamond blade to enlarge the hole or crack into an inverted “V,” with the narrow part of the “V” on the surface of the wall. Then follow the package instructions for mixing and using the hydraulic cement.
Waterproof the Walls
Waterproofing materials that go on like paint fill the pores in the concrete or masonry walls and prevent water from leaking in. To be effective, these coatings must be applied to bare concrete or masonry walls. Start by removing loose material with a wire brush. Then clean off any white powdery “efflorescence” with masonry cleaner. Follow the safety and application instructions carefully. A common mistake when using masonry waterproofing products is to spread them too thin. The goal is to fill every pinhole to create a continuous waterproofing membrane. Brush the coating in all directions to completely fill every pinhole. Add a second coat after the first dries.
Install a Drainage System
The best permanent fix for chronic basement leaks is to install drainage tubing below the basement floor that's connected to a sump basket and pump. You can install a system like this yourself, but breaking out the concrete floor, burying the tubing, and patching the floor is a lot of backbreaking work. Materials to do an average basement will cost $600 to $1,000. Expect to spend $3,000 to $8,000 for a professionally installed system in a standard-size basement.