I have had a leak down into my finished basement. When I cut away the drywall there is an obvious crack that runs to the corner of the basement window. I have sealed outside along the foundation as best as I could and it has slowed the leak, but hasn't stopped it. I would like to try to seal it from the inside before spending the big money on excavating outside. I have two questions...

  1. What is best product to use to seal this crack?
  2. Any suggestions on how to seal behind the metal support? There is only about .5" clearance between the foundation wall and the support.

The leak is coming about right where the crack goes left behind the support in the picture below.

enter image description here enter image description here enter image description here

  • 1
    The best remediation is from the outside. Change the drainage of the area. You will never solve it from the inside.
    – Tyson
    Oct 4, 2016 at 3:22
  • The previous owners had a significant leak in another area of the basement and they were able to solve it by sealing the crack between the sidewalk and foundation outside and then sealing the wall inside. I am not sure what they used, but it has held up just fine. I would think there would be a remedy on the inside since there are plenty of products being sold out there?
    – junta
    Oct 4, 2016 at 13:35
  • Most any kind of Exterior Caulk (latex-based, silicone-based or even Mortar Caulk) would last decades, but use a 50-year Caulk for the best longevity...you won't get 50-years. Slightly dig-out the seam along the building, & both fill it up & squish it in or force in the Caulk...1-inch deep or more ONLY the perpendicular concrete control & expansion joints. Get the Caulk level with the sidewalk first & the next day apply a 2nd Caulk coat that's ramped or beveled away from the building, to negate any sidewalk that's pitched toward the building. It's best to replace the concrete & pitch it away.
    – Iggy
    Oct 4, 2016 at 14:21
  • I have used concrete caulk and hydraulic cement to seal the larger crack outside. This has slowed the leaking, but not stopped it. The water is definitely penetrating down lower.
    – junta
    Oct 4, 2016 at 15:25

3 Answers 3


First I would install a french drain outside. This will keep you from having further foundation damage. Then I would seal it. There are many products on the market for this. I use this product to do my brothers basement. We did two coats. It worked well. But you need to address the issue before sealing the wall. If not you will regret it in the future.

  • Yeah, the issue is that I have a sidewalk along the foundation there and the costs are more than I am capable of doing right now to have someone tear out slabs and put in a new sidewalk with a drain.
    – junta
    Oct 4, 2016 at 13:28
  • If you can't afford to stop the water from the outside, then collect the water on the inside and sump pump it out.
    – mbeckish
    Oct 4, 2016 at 13:47
  • You could do a french drain on the outside of your sidewalk.
    – Mike
    Oct 4, 2016 at 13:54
  • Unfortunately, I do not have a sump pump being that this is an old house. The outside sidewalk has sunk towards the house and that is why the water pools up where it does. I have talked to several contractors to replace the sidewalk but the price to do it is always way under their minimum fees. It sounds like even if the sidewalk was graded correctly, I still may end up with water issues since I have this crack inside? It seems like everyone has a different solution, which makes it tough to figure out.
    – junta
    Oct 4, 2016 at 15:58

If it is not feasible to repair the crack from the outside, it can be done from the inside. There are a number of fast-setting mortars/hydraulic cements on the market that will accomplish this. The most permanent (but time-consuming) method is to use a cold chisel to open up the crack but to rebate it on both sides as you go. Think of it as being similar to a bath plug with the narrowest part at the surface tapering back to the widest area. Now fill the crack step by step starting at the point of lowest pressure and working to the point of highest pressure. Hydraulic cements should be mixed in small quantities to a putty-like consistency which you can press into the opened-up crack. As it activates, it will get warm in your hands and you have about 2 - 3 minutes to place it. Allow the plug to stand a little proud of the surface as you go. You can smooth it off as soon as you have finished with a trowel and/or scrubbing sponge. If the mortar is setting too fast, used iced water to slow the set. Conversely, warm water may cause a flash-set. Once completed, there are a number of products, such as Thoroseal, that can be applied to "tank out" the concrete walls from the inside and make them impermeable.


I had several cracks, some leaking, in our basement when we started finishing it. I used a urethane foam product from RadonSeal (http://www.radonseal.com/crack-injection/diy-injection.htm). I didn't get anything up on the walls for nearly a year after I filled the cracks and never once saw water in any of the previous offenders. Another year and a half later and I've still not had any problems.

Make sure you take care of any grading issues outside, and/or sealing between the foundation and adjacent sidewalk - no point in making the foam work harder than it has to.

Hydraulic cement is not meant to be waterproof, just FYI.

  • I was thinking of that product as well. Did you use any kind of sealer on the wall after?
    – junta
    Oct 5, 2016 at 1:02
  • I did use their spray-on sealant as well. Harder to gauge the effectiveness of that, but I figured it can't hurt.
    – Drew
    Oct 5, 2016 at 1:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.