How to Fix Sticking Window Sashes
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Before you start planing or sanding back, taking material off sticking sashes. - THINK why it’s changed? A build up of paint is obvious and can be stripped or sanded back but the problem could be deeper.
The underlying cause could be related to the wood swelling on either the frame or the sash or both. If swelling is enough to cause sticking then it’ll probably be enough to cause rot so the problem should be properly addressed.
On opening lights the other thing to check is the hinges, these might be loose or distorted.
Moisture swelling the sash
The best way to deal with a moisture swollen sash is to remove the sash from the frame (but you can leave it in for a less thorough job). Stripping the paint off back to bare wood will allow the timber to dry out and ensure any repainting will be sound.
With the paint is off, the wood will dry quickly and evenly, a few days up to a week or two indoors should see it settle back to its proper size. Hey Presto, no more sticking sash. All you need to do is repaint, this time with a micro-porous paint system or my preferred option, Linseed Paint.
If it’s the frame that has swollen, again strip the paint off. As you can’t bring it inside to dry out it might take longer and a water based primer will keep the worst of any rain off or my preffered option a coat of linseed oil.
Note on swollen sliding sash windows: Often people assume the moving sash is part that has expanded so they trim it down. The problem can be that the inner and/or outer lining of the box frame has expanded. If the outer edge of the linnings are restrained against the walls, then any natural expansion as humiditly level change will force the pulley stile on to the sashes. Sliding sash windows should only be fixed in to openings at the cill and top rail, the linings should not be mechanically fixed.
Other distortion might be down to the joints coming loose. See Fixing Loose Sash Joints. Make sure it’s glued back in the right shape, bear in mind that might not necessarily be square. You should also check the glazing putty is sound.
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