Concrete Cill repair - total novice.

26 Apr 2012
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United Kingdom

I'm thinking of having a go at repairing a cracked cill in my flat, but having never done anything like this before I thought I'd ask some advice / check my plan before starting.

I've attached a picture of our cill, and the one next door which I assume was repaired by the council (ours is an ex-council flat).

I've had a look online at the various videos and help-sites and cobbled together a plan from what they said to do, please correct me / tell me I'm an idiot!

1/ Wire brush to clean loose concrete and take off some/most of the paint that's been added.

2/ Paint exposed metal with some kind of primer - I'm wondering if hammerite would do?!

3/ To give the concrete something to hold onto, either
Drill holes and insert "rebar" spokes that protrude a little along the edge
"Tie" a length onto the exposed hooks long the edge.

4/ Build some shuttering

5/ Coat the edge with cement paint - mixture of cement and water to pain consistancy

6/ Mix 3 parts sand to 1 part cement to a butter-like consistancy (with a little washing up liquid to make it mix easier?)

7/ Fill and pack the shuttering

8/ Shape the new cill edge, lightly brush it to help run off. Cover with plastic to keep wind / rain / sun off new.

9/ Leave for a week.

10/ Cross my fingers, take away shuttering and touch-up

Anything I'm doing wrong / missing? I've read a few places that I should dampen the new concrete while it dries?

Any advice would be great!

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No 5, Id use a sbr slurry.
Dont use fairy liquid, use Febmix.
Fit either some sash cord or half round beading in the bottom shuttering to create a drip.
Use a plastering sand with some glass fibre strands added in the mix, plus a dash of sbr.

This is looking like I need more things to do this than I'd hoped!

Couple of questions, sorry, this really is a delve into the unknown for me:

sbr slurry = sbr mixed with cement to a paint consistancy?

Release oil = Diesel? Not expecting to use the SBR of febmix again any time soon, would be good to not have to buy anything else!

Fibreglass strands - how much should I add and will I be able to get these from Jewsons?

And the drip - this is just a hole drilled into the bottom of the shuttering with a bit of cord fed in?

Also, I'm ok to use Hammerite on the exposed/slightly rusty Rebar - was half expecting to be called an idiot of even suggesting it but I've plenty left over from the railings!

Sorry to be a pain.
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Mix the sbr with cement powder to form a thickish but paintable consistency.
You can use engine or cooking oil for the shuttering.
Get a small bag of glass fibre strands, aids the strength.
The sash cord or half round bead needs to be fixed on the bottom edge of shuttering, the whole length, so as when its all removed you have a preformed drip channel.
Have a look under some coping stones or old wooden window cills to see what I mean.
Ok, thanks!

Starting to think I'm being a bit over ambitious here having never so much as bought a bag of cememt before, but I'll give it a go!

Many thanks.
If this is a flat, isn't the landlord responsible for the external structure?

Anyway, the problem with concrete repairs and rusting reinforcement, is that the concrete there as most likely failed due to carbonation ie high alkaline content in the concrete allowing the steel to rust.

I't never a case of just shuttering and putting more concrete or render back, as the reaction will continue and the new stuff will just fall off.

There needs to be some proper cleaning and stabilisation of the concrete before repair

Products from Sika may be advisable or something similar

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