I am in the process of painting my timber frame windows and when cleaning and sanding down I have noticed that there is a small gap between the window pane and timber frame on the interior (the stuff which was in the gap has come away etc. when prepping). I am wondering what I can use to fill the gap and then paint over it to give it a nice finish (the gap looks pretty ugly!).

Here's a picture of the gap.

enter image description here

I'm aware of window putty and decorators caulk but do not want to use the wrong thing and create more work for myself! Based in the UK if that helps with product recommendations.

  • When you say "timber frame window" do you simply mean a real wood frame, as opposed to vinyl, aluminum or other material? Despite the picture, I keep envisioning a timber framed house with very large timbers (instead of dimensional lumber) or even a log home type construction and am wondering how that works for a window and how it applies to the window in the question.
    – FreeMan
    Commented May 18, 2020 at 17:31

2 Answers 2


I would recommend using glazier's putty, not "regular" caulk. Glazier's putty is designed to bond to glass and wood/metal/vinyl and to stay flexible for decades to provide a good seal for your glass.

A simple search for "glazier's putty" turned up quite a variety of options. This page was one of the first and describes and ranks several different varieties for different applications. (No affiliation with the site or guarantee of the suitability of his opinions to your application.) If you were a pro and staking your reputation and income on your choice of putty, this might be very valuable. Since you're only doing a few windows, you may just want to go with the smallest tin you can find at your favorite local hardware store.

Several sites indicate that it can be more difficult to work with than simply squirting caulk from a tube. I have reputtied a couple of windows and didn't find it terribly difficult. It's rather greasy stuff, though, so expect to give your hands a good scrub before grabbing a sandwich for lunch.

  • Thanks @FreeMan. I have two different answers and I'm not sure which is best. I presume Glazier's putty is best (since it's literally for glass...) but I have only found this being used externally. Does it really matter which is used internally?
    – tda
    Commented May 18, 2020 at 17:26
  • 1
    That @tda is an answer I cannot provide for you. It's what I would do because I'm a "use the right tool for the job" (whenever reasonably possible) kind of guy, so I would consider purchasing a little container of it a reasonable expense to ensure it was done "properly". Whether it would be any better or not on the inside of the window, I really can't say.
    – FreeMan
    Commented May 18, 2020 at 17:29
  • +1 right tool for the right job. I've just had a look and it's pretty inexpensive and I need to replace some window panels over anyway (requiring putty) so might as well do both at the same time. Thanks for your help!
    – tda
    Commented May 18, 2020 at 17:30
  • As an added bonus, @tda the "right tool for the job" mentality helps you collect a shed full of tools and we all know that "he who dies with the most tools wins"! :) Glad I could help.
    – FreeMan
    Commented May 18, 2020 at 17:33

Yes, that appears to be old, dried caulk. The new caulks don't crack like they used to. Get yourself a tube of silicone caulk. It comes in clear and white and possibility other colors. Make sure you get one that's paintable. Clean out the old gap completely. Spraying in some white vinegar will help dissolve the old caulk and make it easier to remove. Wipe down with water and let dry completely. then apply new caulk, following the directions on the tube.

  • Thanks @JACK. From a quick read online, I can see that silicone caulk is pretty common for uPVC windows but can't see it being used internally for timber framed windows. Would this yield a similar outcome to glazier's putty?
    – tda
    Commented May 18, 2020 at 17:24
  • @tda I've used it from Florida to Chicago with great results. The trick is that the wood has to be very dry. I do like the putty when replacing panes in a wood frame because you can build it up whereas caulk settles and runs.
    – JACK
    Commented May 18, 2020 at 17:44

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