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Casting window sill

Posted: Tue Jun 27, 2017 8:44 pm
by Henrythedog2
Need to cast a new window sill any recommendations for concert,sand type
Was going to use 18mm shuttering ply for the casting, going to be 5ft long but not sure whether to cast in situ or on bench.
Planning on putting some reinforcing rods in and sash cord to form drip
Any advise welcomed
Thank you


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Re: Casting window sill

Posted: Tue Jun 27, 2017 9:06 pm
by davyp1
Not knowing the cross section of your cill I am having to make a bit of a guess, but my feeling at 5ft long is to advise casting it in situ.
Saves the possibility of an heavy lift later.

Base your mix on - 1 x Ordinary Portland Cement : 2 x Sharp Sand : 4 x 20mm Aggregate.
18mm ply is fine for the shuttering & sash cord for the drip; don't forget to soap oil the shuter
prior to the pour.
With your Re-bars, remember to allow say 35mm of cover. (distance from rebar to face of conc.)
Remember to trowel a slope to the top of Cill to discharge water.
If you own a 'Nosing' Trowel, you could trowel a small nosing round to the top front edge.
Another point, don't under estimate the force given by the wet concrete, be sure to back up the shutter by
any props and supports you can get in.
You can not over prop!
After 24 hours, remove the props but leave your shutters at least another day.

Any other questions, just ask.


davyp1

Re: Casting window sill

Posted: Wed Jun 28, 2017 7:14 am
by Grendel
I cast a fair few during my apprenticeship. At least one I didn't put enough propping in and it moved so I can only echo davy's comment about that. He's also right that casting in place does solve the problem of moving it although casting it upside down does allow you to cast in rebates and slopes to the top surface with ease although that's still possible in situ.
You may wish to experiment with the mix too. Different colours of sand and white cement can effect the finished colour should that be an issue .

Re: Casting window sill

Posted: Wed Jun 28, 2017 7:56 am
by dewaltdisney
I am not sure if it helps but a guy I know told me of some chap who did this job and put a thin sheet of ply over the top of the fill and vibrated it with a palm sander. This helped to get it settled well in the mould. I never saw it first hand but it sounds like a good idea and I stored it away in my mind for future reference......and here it is :lol:

DWD

Re: Casting window sill

Posted: Wed Jun 28, 2017 9:58 am
by davyp1
Afterthought!
I never mentioned 'compaction' !
While I have never heard DWD's tip before I can see it working. Yes. just a much smaller version of the 'poker & snake' we used to use on big pours.
For the Cill job, just adding the concrete in two inch layers and compacting from the top with a short length of 1"x1" end on then finally tapping the shutter with light hammer would be sufficient to remove air bubbles & honeycombing.
The finish on the top of the Cill will be only as good as the effort put into it.
Fist rub over is with plastic float and serves to put the aggregate down from showing at the surface. Then perhaps a 2nd rub over with plastic half an hour later. Follow this with the steel float say three quarters of an hour after that then a couple of times more at similar intervals. By then, you should be getting near to a 'polished' surface.
Unfortunately it takes just the same amount of time to finish one small item as say a large landing slab!
Weather has an effect too, on hot sunny days the concrete cures quicker and you may need to cover with hessian or similar between floats.

davyp1

Re: Casting window sill

Posted: Wed Jun 28, 2017 7:24 pm
by cotswold builders
Grano is a far better material for casting cills. you will also be able to get a better polished finish.

Re: Casting window sill

Posted: Wed Jun 28, 2017 7:33 pm
by Henrythedog2
Are they likely to have "Grano" in the merchants?

The original sill or cill (a interesting debate in itself) was made of what would appear to be sea sand with a few yellow stocks thrown in for reinforcement


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Re: Casting window sill

Posted: Thu Jun 29, 2017 10:37 am
by Henrythedog2
Just bought some grano 100 kg and 12 reinforcing bars, what is the mix ratio please


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Re: Casting window sill

Posted: Thu Jun 29, 2017 1:10 pm
by Henrythedog2
Thats a couple of 12mm bars


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Re: Casting window sill

Posted: Fri Jun 30, 2017 3:43 pm
by cotswold builders
6 Grano 1 building sand 2 cement

A half round wooden bead might be easier to use instead of sash cord.

Re: Casting window sill

Posted: Fri Jun 30, 2017 3:46 pm
by Henrythedog2
Thanks doing it tomorrow


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