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Add Gutters and Extend Downspouts
If your basement leaks after it rains and you don't have gutters, consider adding them. Gutters catch the rain and channel it to the downspouts, which direct it away from the house. Whether you're installing new gutters or already have them, be sure the downspouts have 4- to 6-ft. horizontal extensions to move the water away from the house.
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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.
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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.