rain damage to window cills

19 Nov 2006
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United Kingdom
Some background - the house is a late 80s 2 story build with fairly normal brick and cavity wall construction. uPVC windows were installed in the early 90s.

After last winter's heavy and persistent rains we ended up with some water damage to 2 of the window cills on the inside of the house on the ground floor on the south side. We never saw any signs of water pooling on the cills or the like; it would appear that the edge of the cill near/under the window was exposed to water which then wicked through to the inside and caused the outer edge of the cill of swell up.

I've had a close look at the sealant between the uPVC frame and the house wall and while it looks a bit weathered it seems firmly attached to both the frame and the brick work. That said I'm happy to dig it out and replace it. The seals between the double glazing units and their frames look fine and drain holes in the frame are clear. The brickwork and pointing looks fine..

But is there something else I should be looking at? Any advice would be appreciated.
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The seal between the window and cill has more than likely failed. It would only have been a mastic line but after all this time I would suspect that it is no longer doing it's job or the amount of rain has just overwhelmed it.

Without taking the window out you will not be able to seal it and I wouldn't recommend that anyway, a whole new can of worms! But you might be able to cut away at the bottom corners of mastic and pump some new silicon right up to the back edge of the window and seal off the side of the cill, the cill should have an up stand across the back so hopefully this will give the water no where else to go but out.

Any drainage holes you can see, try pouring in some hot soapy water. Insects love building nests in these and they do get filled up with dirt over time.

Hopefully this will sort it out for you :)
Thanks for the quick reply. What you say makes perfect sense given the weather we had and the prevailing wind direction.

You say "Without taking the window out you will not be able to seal it and I wouldn't recommend that anyway, a whole new can of worms!" Can you expand on what difficulties I might encounter?
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No, pretty sure it's not condensation - the windows are double glazed and condensation has never been an issue. There are also no signs of water staining or water having pooled and evaporated.

We manage the humidity in the house being careful with ventilation and bath/kitchen steam and occasional use of a dehumidifier if needed.
To take out your window would involve basically re-fitting it and at the age they are there's no guarantees that bits may not break, rendering it in a worse state than before.
Replacement parts are usually easy to find but the profile will not be readily available, if at all.

If your confident then go for it but maybe just try sealing up the corners to see if that works first might be the best option. :)

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