How do I repair a crack in a brick windowsill? I assume that it needs to be sealed to prevent water from getting in, especially during the winter when it could freeze.

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The other side of the window has a similar crack that was repaired by the previous owner of our house.

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It appears they may have used some sort of epoxy. Is that what I should do for the other side as well? If so where do I get it and how do I use it?

  • These look like new replacement windows, how recent? How old is the house in comparison.
    – Jack
    Commented Dec 27, 2015 at 17:51
  • The house is 20 years old and these windows are original to the house. They are crank style with aluminum frame. Commented Dec 27, 2015 at 17:54
  • The trim on the window is what cracked the brick, it should have been cut shorter above the brick to allow the expansion and contraction of the framing let the wall move behind the brick. The window I presume still works ok? Does it work better in the summer and worse in the winter, for what you may experience in Cali... How long ago did you notice the cracks? Is your house on a concrete slab or is the floor wood frame construction? Your answers will help answer the question accurately
    – Jack
    Commented Dec 27, 2015 at 23:18
  • The house is wood frame construction over a basement. I'm located in New England. The window works fine. I only moved in in August so I haven't tested the window in super cold weather yet. I noticed the new crack shortly after I moved in and it is worse now 4 months later than it had been. Commented Dec 27, 2015 at 23:26
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    Just as a mention, it looks like clear silicone in the crack and a bit smeared onto the face of the brick in the corner. That will suffice for caulk on the other side. The stuff is messy.
    – Jack
    Commented Dec 28, 2015 at 1:37

2 Answers 2


If the cracked bricks are loose (as in when you wiggle them they move) they should be removed and new brick installed (or clean the old ones of mortar).

If the cracked bricks are sound and secure the gaps should be filled ,as you noted, to keep water from further damaging the sill.

There are many colors of concrete-type caulking, so if desired the gaps can be filled with a red color and the joint with a grey color. Use a urethane caulk for greater longevity.

A two part epoxy would work just as well as a caulk but it would be difficult to color match (if that is important). Epoxies can be purchased at a local hardware store or a contractors warehouse.


If your window still works in the wintertime, it will tell me that the window has not settled to hard on the brick sill at least not like the trim has. All you would need then is to caulk the cracks so water does not get in there.

If the window does not act properly, I would suggest having the brick sill removed and lowered 1/4" so there is room for movement above the sill.

If you do not choose to lower the sill, take a look at it in the summertime, there should be a gap at the trim to the brick by then, when the humidity raises.

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