Caulk as weatherstripping?

Question

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?

Answer 1

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.