There is a large gap underneath the bottom sill of the window, that is currently caulked when the house was built.

I would like to strengthen the waterproofing here. I'm thinking backer rod with Vulkem 116 caulking.

Would this be the best way?

Here is a picture of the window, it's the channel underneath the sill. window


1 Answer 1


I have built both residential and commercial buildings. Every scenario such as this we use expansion foam which can be found at most hardware stores. Then once hardened, carefully scrape back some to leave room for any type of silicone caulk or whatever you choose for a finished look.

  • It is a low expansion foam, as in Great Stuff window and door?
    – v15
    Aug 25, 2016 at 17:26
  • Yes that is correct. homedepot.com/p/… Aug 26, 2016 at 6:31

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