Seal between windowsill and window frame

4 Mar 2017
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United Kingdom

I have painted windowsills and uPVC window frames (both white). I need to fill the gap between them (maybe up to 5mm gap).

Should I use an exterior caulk such as this available form Screwfix -
This might make repainting the sill easier next time as paint will stick.

Or use a white silicone sealer (which cant be painted). When remaining I would only be able to paint to the edge of the silicone.

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Use a neutral cure sealant (WP 100 etc) which is much nicer to work with and doesn't suffer peeling away like regular silicone sealant does.

If in any doubt about painting over it, go over it first with Zinsser 123, which can be applied to anything, then any paint can be applied after that.
Bear in mind emulsions crack and graze when painted over acrylic, unless primed with something.
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Is this gap between the window frame and the sill OUTSIDE?

Does the gap run along the full length?

Do all the windows have this?

If so, it sounds like a drainage gap, which you don't want to be blocking.

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