Crack in concrete window sill...

Torby · 8 July 2009 at 8:22AM

I have noticed a crack in our concrete window sill, I reckon (not being too DIY savvy) that its caused in part by being a cheap product and water ingress which during the winter freezes etc and opens the crack further. At the minute the crack at its widest is only 2 or 3 mm wide.

Can I fill it with a silicon based product (or one you can recommend) and then paint over it, hopefully the plugging of the gap will stop water getting in this winter and we can get another few years out of it.

Its not a high level window sill, its not likely to injure anyone if/when it breaks and it is towards the outside edge so its not going to cause any structural problems.

Lorian · 8 July 2009 at 8:26AM

Not silicon, its terrible to paint over. Fill it with exterior polyfilla and paint with a suitable exterior paint, or my preferred route would to be to make a sand and cement mix to roughly match the concrete (you have to make some tests on a spot of wood or something and let them dry). Then fill the crack with a resonably moist mixture, being as carefull as possible to fill inside the crack, and then clean outside with water. That way you don't have to paint it if you don't want to. if the crack is straight you can use masking tape down the edges. make sure you use a flexible pallet knife to do the filling.

You could of course re-inforce the crack further, maybe from undeneath if visible, with a metal strap. Sometimes I have cheated and packed the joint with expoxy putty before over-filling with the motar, and it's quite effective.

Torby · 8 July 2009 at 9:16AM

thanks Lorian, as its painted (brown) looks like exterior polyfilla is the route to go then.

savemoney · 8 July 2009 at 10:27AM

I used exterior polyfilla for this job a couple of years back and also patching up chips on some bricks before repainting It did the trick

Crack in concrete window sill...

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