concrete window sill

I have a 6 foot long concrete window sill under my kitchen window. Part of it had spalled off along the line of the r bar. The broken part is not as far back as the house wall. The sill is at least 40 years old and is weathered. I think there are 2 ways to do a repair; the first and both most expensive and messy is to cut out the old sill and replace, this could be a big job although being at ground floor level will help. The alternative is for me to shutter the sill and pour concrete in to make a patch. I have drilled out a few holes so could insert screws or similar to give a key to the old sill. The repair would of course not match the old sill unless I brushed all over with a thin layer of cement wash. Has anyone tried a repair like this and do you think that it will work? Thank you

Reply to
Stewart
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Its not a job I've done. At least use ss screws. Cement/sand tends not to survive long in thin layers. I expect epoxy mortar would do better - and match even less of course.

NT

Reply to
meow2222

If you use resin anchors into the old cill (or 10mm stud, galvanised of stainless) held in with a vinylester or polyester resin eg

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it will be fine.

It's basically the method they used to widen the decks on the M25 bridges back in the late 90's on the southern section (Merstham area). Only they used f*ck off big bar, and probably a really fancy resin. After they cast the extra deck, they left the shuttering ply and its supporting scaffold in place for a very extended time (months).

You of course could remove the shuttering after a day or so.

What I would do in your case is to paint a cement slurry over the face of the old cill so the new one bonds to it s well to avoid a crack water will get in and freeze.

If your new cill section is very thin (50mm or less) I would also add some SBR to the mix (both slurry and new concrete). But you will have to grease your shuttering (literally - grease or vaseline) or you will not get it off!

As to appearance - your idea will probably work. Or perhaps paint the lot with some floor paint in black or red or grey. I did my tile cills like that and they look very smart.

Reply to
Tim Watts

I converted a kitchen door + window into a large kitchen window by bricking up the doorway and shuttering and pouring cement to extend the concrete window sill. It worked perfectly well. In my situation, the brickwork was rendered, pebbledashed and painted to match the rest of the back wall and the sill was painted to match the others so I didn't skim cement over the whole caboodle. I suspect that weathering would have broken up a thin skim anyway and a thick skim would have started to bury the window frame.

Reading your first paragraph again: six foot, forty years ago. That could have been my window, that could. You are not in Leigh-on-Sea by any chance? In which case I deny everything.

Nick

Reply to
Nick Odell

Nick, I live in Fife with house about 1km from the sea.

I converted a kitchen door + window into a large kitchen window by bricking up the doorway and shuttering and pouring cement to extend the concrete window sill. It worked perfectly well. In my situation, the brickwork was rendered, pebbledashed and painted to match the rest of the back wall and the sill was painted to match the others so I didn't skim cement over the whole caboodle. I suspect that weathering would have broken up a thin skim anyway and a thick skim would have started to bury the window frame.

Reading your first paragraph again: six foot, forty years ago. That could have been my window, that could. You are not in Leigh-on-Sea by any chance? In which case I deny everything.

Nick

Reply to
Stewart

Well an old council building near me seems to have had the patch up method, but you can see the join, to coin a phrase. I can feel the difference myself. Quite how long it will keep together with frost and water etc, is anyone's guess. Its been in a couple of years so far, but its quite sheltered.

I suspect its going to be a suck it and see thing. Always makes me laugh though when upvc windows are fitted to buildingslike this, they still have a dinky little window sill that comes out slightly over the concrete one. Brian

Reply to
Brian Gaff

Thanks Phil; your proposal is much nearer to what I am now going to do. I intend to cut off the front of the sill along the line of the r bar and then scabble the top surface of the remaining part of the sill. I shall shutter it, put in some ties as suggested and then pour concrete, finally running a thin film of mortar over the scabbled top of the sill. I do not have a vibrating poker or plate but think I can rig up a power drill in some way to act as a vibrator; perhaps my powered jig saw could do the job and then just discard the used blade. Thank you all for the ideas.

Forget the cement wash idea, cement is useless at adhesion on it's own.

You almost had it when you said make a shuttering and pour concrete, but you can't do this in a patch otherwise it will look hideous, but that's up to you.

Is there any reason why you can't make the whole thing bigger?

Shutter it out about 50mm at the front and the same at each end, not forgetting at least an inch on top.

Mix granno and cement at 3:1 and use this, bear in mind that the rusting rebar will continue to do it's dirty work unless you remove it where it's corroded. Also, you'll need a key, either SS screws into the existing concrete or partial removal of existing concrete wherever possible. PVA everything before you add the shuttering, and for a dripper, tack a length of 12mm rope to the inside of the bottom shuttering about an inch back from the front of the cill, sometimes this sticks in the concrete when you remove the box, but can easily be pulled off later, leaving a dripper.

Use vibration to ensure strength and eliminate air bubbles, IE use a hammer all over it once filled, which means the shuttering will require propping both upwards and into the house otherwise it will fall forwards and the granno will run down the wall.

Once the shuttering is removed (after at least 4 days) you can go over it with exterior filler to fill any air holes, leave for a week or two to fully cure, then paint with masonry paint

I've done lots like this

Reply to
Stewart

A sander on the outside of the shuttering will vibrate it

Reply to
alan_m

A sander on the outside of the shuttering will vibrate it

Reply to
Stewart

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