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Before I begin, yes, I know that generally caulking does not serve the same purpose as weatherstripping, and the usual recommendation for windows or doors is to use weatherstripping.

The problem is I've got several old windows which it is impossible to weatherstrip properly and still have them close completely. I've tried different types of weatherstripping and either gaps remain that open to the outside and let in all manner of undesirable critters, or it becomes impossible to close the window. I've had the idea of applying silicone caulk to the areas I am unable to weatherstrip, putting clingfilm over them, and then closing the window over the clingfilm, thus shaping the caulk into the correct shape to seal the gap. Then I would let the caulk cure, and remove the clingfilm, leaving the properly shaped caulk behind.

Is there any reason that this seems like a bad idea other than this not being the usually recommended way to use caulk?

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    Sounds like a good idea to me. I suggest you try it and let us all know how it works out. This could be good info for future questions like yours.
    – RMDman
    Commented Mar 26, 2023 at 17:20
  • 1
    @crip659 the windows are casement windows so I think it should work for the sides as well.
    – Catherine
    Commented Mar 26, 2023 at 18:32
  • In that case it should work well. It does not have much give to it, so the best sealing is when the windows are fully closed/locked, once the caulking has set.
    – crip659
    Commented Mar 26, 2023 at 18:52
  • I would also have you add a new question with pictures showing the window/s and frames with the gaps. Someone here might have a simple fix so the gaps are not so bad and regular weatherstripping will work. Wooden windows can be simple to fix if the problems are minor.
    – crip659
    Commented Mar 26, 2023 at 19:52
  • Commercial (not big box crap) weatherstripping exists (google Pemco -- you'll end up getting it from a specialty supplier) that would probably meet your requirements. A picture of the problem would help. Commented Mar 26, 2023 at 21:07

1 Answer 1

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I can think of just two reasons why this may not work as intended.

  • Silicone isn't terribly flexible or compressive. If there's much slop at all in your windows you won't get the seal you hope for. It just isn't soft enough to handle lateral play.
  • You'll need to lubricate with something like (ironically) silicone spray. Silicone caulk is rather sticky when sliding against some surfaces. You might not think that this applies to casement windows, but the hinge-side seal does slide somewhat during the final sweep of the sash. Because it's a very long strip it imparts quite a bit of friction.

Otherwise, it may just do the job.

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  • It will probably need replacement every two or three years to keep the seal tight. My door used a lever to close and had an adjustment to tighten/increase the closing force to keep the seal good.
    – crip659
    Commented Mar 26, 2023 at 19:46

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