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Community and Q&A

How to repair the concrete sill under our front door?

allspiritseve | Posted in General Questions on

We’ve been having some issues with water leaking into our basement under our front door. We have a metal threshold over a concrete sill, and our front porch is a concrete slab about 4’x6′. There are a number of weatherproofing issues we need to address, but the most urgent is the concrete sill under the door which has been crumbling for a while and presumably is the source of our leak. I’ve removed the threshold and cleared out most of the loose concrete so I could see what was underneath. Here are a few photos:

Now that I can get a good look, my best guess is water was entering the house along the black tar paper, and not a crack as I had first thought.

Given the porch is level and roughly flush with the subsill (the darker concrete in the photo), I’m not quite sure how to properly fix this. I can pour a new concrete sill, but water is just going to sit along the seam and eventually (I assume) break down the concrete in a few years. What’s the right way to fix this?

Any advice would be much appreciated.


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  1. GBA Editor
    Martin Holladay | | #1

    As you probably realize, the builder of this home made two big mistakes:

    1. The builder forgot to install any sill pan flashing under this entry door.

    2. The builder forgot that a concrete stoop needs to be lower than your door threshold to make drainage possible.

    This is a tough one. Do any GBA readers have any suggestions? I know that one solution is to demolish your front porch, and rebuild everything correctly. That would work, but it's expensive.

    If you can do some more diagnostic work and figure out how water reached this area, you might be able to correct the flashing problem than allowed water to enter your wall assembly in the first place.

  2. allspiritseve | | #2

    Thanks Martin. We'd definitely like to find an alternative solution besides demolishing the front porch.

    My biggest concern at this point is the seam between the existing concrete surface and a new poured concrete sill. Would installing some L-shaped metal flashing along the front of the sill be worthwhile? It seems like there must be a way to adhere it to the concrete porch that would be waterproof.

  3. GBA Editor
    Martin Holladay | | #3

    I'm not sure what you mean by "the seam between the existing concrete surface and a new poured concrete sill." What's existing -- the house slab, the porch slab, or both? What's new concrete -- just the narrow band directly under the door?

    If you want to adhere metal to concrete, I'm pretty sure that epoxy would work. Here's a link to one product:

    The only thing I'm unsure of is whether the thermal expansion and contraction of the metal would eventually break the adhesive bond. When in doubt, call the adhesive manufacturer, ask for their technical help department, and get advice.

  4. allspiritseve | | #4

    Existing concrete being the porch slab and subsill (the roughly level surface you can see in the photos). New concrete would be a replacement sill, so yes, a narrow band directly under the door.

  5. tallpinecottage | | #5

    Cory -

    What did you end up doing as a fix?

    I'm dealing with a fairly similar issue. Need to replace existing wooden threshold (rotten, bug infested). Putting in a prehung door with metal sill, but not sure what to put under the new threshold to create a 'curb' to keep water out.

    1. Expert Member
      Akos | | #6

      Pour a new sill underneath with concrete. Make sure the top of this is sloped and cover it with peel and stick for water protection. You can use quick set mix so you can do the whole thing in a couple of hours.

  6. tommay | | #7

    As Akos said, pour a new sill and make sure it's pitched or make a small channel a foot or so in front of the doorway to capture and redirect any water heading towards the sill plate.

  7. sjmacd | | #8

    I have a similar issue and a builder friend recommended hydraulic cement.

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