Fixing down a new hardwood window sill that's bowed


27 Oct 2003
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United Kingdom
I've replaced several window sills successfully with hardwood, fixing it to rendering and brick that was left when old quarry tile sills were removed.

This time the window sill is in a newish extension so I'm fixing to a plastered surface.

The hardwood window sill is bowed in the middle. The joiner said that this was 'normal' because it is only 20ml thick. Over a length of 1850mm it bows up by 25ml in the middle. I can get it down flat if I use all my strength.

He told me to use High Grip and that would hold it flat. But even if I glue it and sit on it till the glue's dry, won't the spring in the wood just rip the plaster off?

Any suggestions to straighten the wood out?

Thanks for reading, hope you can help.

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You can make cuts in the wood on the under side to take it's strength out, approx 30mm apart. Just make sure your cuts are not to the front edge and can't be seen when fitted.

Awesome! Some an easy solution and such a quick reply! Thank you very much.

How deep should I make them?
I would say 5mm - 10mm. Make sure you only cut the under side and only cut the width of the brick work. Any further and it might show.

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Magic. Thank you so much Andy. Has put a smile on my face :)

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