Some muppet has managed to knock the corner off a stone window sill. The lump is sizeable, about 3"x2", so I want to reattach it. What would be the best way of doing this?
I don't know what sort of stone it is - but the exposed surfaces are pretty soft and crumbly.
I'm thinking: apply dilute PVA, allow to dry, then Araldite... would that work?
The sill is painted, and I'll be repainting it when finished which at least should hide a multitude of sins.
Stick the lump back in place with "No More Nails" and some wide masking tape. Allow it to cure for a day or two. Use a small masonry drill, about
3 mm if you've got one, and drill through the thickest part of the lump and into the sill, a good 40 to 50 mm in, and squirt some more "No More Nails" into the hole. While it's still wet, hammer in a plastic pin of some kind, part of a plastic knitting needle or the like, to hold it place firmly. Don't use metal pins unless you know they won't rust and pop the lump back off in a couple of years time.
To firm the lump back into place with the "No More Nails" in between, tap it firmly with a block of wood and a hammer. Keep tapping the stone until it sits quite flush with rest of the sill again. Wrap a bit of wide masking tape or PVC tape over it in a couple of places to make sure it won't slip. You can also use bits of string on nails tapped into the mortar joints of the surrounding stonework.
Not much point in that, as the PVA will set the strength, and PVA isn't waterproof anyway.
I'd use resin as used in car fibreglass. There's very possibly something better, but that's cheap and readily available from the likes of Halfords. It's a two pack material with a hardener. It will obviously want well supporting till it sets.
Thanks for the advice, all - the above is the option I went for!
Seems to have worked OK, but I'm worried about the longevity of the repair, because of the stone being so crumbly. Point taken about not PVA-ing first, and I didn't do so; however the filler really didn't stick well to the substrate and I can't see it lasting long TBH. Isn't there anything else that would do a PVA-like role under these conditions?
I didn't try pinning the repair as others suggested; the missing lump was far too friable to be drilled.
A late reply to this thread. I had to patch up some stome cills a while ago and I enquired here about it - search this group in Google for the subject "Crumbling stone cills" if you want to see what was said.
I ended up using this stuff:
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one case I had to do pretty much what you're describing. I didn't have the missing bit. I just built it up using the cement. I clamped a bit of wood to the underside of the cill to support the cement as it set, but it does go off very quickly. I got a nice finish on the top and front faces by polishing with a float before it set completely. It seems to have lasted pretty well so far, but I only did it a few months ago.
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