As you can see from the photos. The window fits pretty snug. I planned on using a little expansion foam on the sides with caulking. And just caulking the top. The bottom, however, is tricky to me. The weep holes in the front of the window would allow the water to run out onto the front of the cinderblock and then back down into the cinder block. I'm not supposed to caulk the bottom of the window but I really dont' want water to drain back down into it. See this photo https://photos.app.goo.gl/t7FvgELw4IZ3Bj6h2 . See the lip of the cinderblock? The water can go back down under the window.

I just had an internal basement drain system put in around the perimeter of my house going to sump pumps and weep holes in every block at the base to allow it to drain into the system. But I didn't know if allowing this little bit of water in the cinderblock could weaken it.

Should I just fill the top cinderblock with expansion foam?

1 Answer 1


Weep holes are supposed to be outside of the facade or over a downward sloping sill. Windows are supposed to sit in a frame. Caulk will not seal the window for long in your situation. Also, be aware that cinder block is porous, so if you just put a little around the edges, water will go right around it through the cinder block.

Basically the problem is that you have no frame, so you need to get a smaller window and build a frame, or chip out enough of the cinder block that you can fit a proper liner and sill around the window.

  • Tyler is right on. Additionally, the exterior of the block needs to be treated with a water-tight sealer, spray on at a minimum. The new foundation wraps are great but expensive. P.
    – Paul Logan
    Nov 18, 2017 at 20:04
  • So you're saying if I caulk along the base of the window, I will have water pool and go into the cinderblock. What if I used aluminum flashing going from the back of the window all the way to the lip of the front of the window, to force any water back out. Acting like a sill? Nov 19, 2017 at 13:26
  • Thank Tyler. I will seal the block around the window. That's a great tip! Nov 19, 2017 at 13:31
  • @EricMiller I don't think you understood my answer. Just to repeat what I what I already said: if you caulk the gap between the window and the cinder block, it will do nothing because water can go around the caulk right through the concrete block which is porous. Nov 19, 2017 at 13:46
  • I took your advice and I ordered a smaller window height wise. I will put a sill in there. Thank you both Paul and Tyler Nov 19, 2017 at 14:06

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