concrete window sills?


Has anyone ever made their own concrete window sills? I have a 150 year old Victorian home that has had three additions over it's life and I swear that each window has a different window sill, some wood, some concrete some??? Anyway since the house now has all new windows in I'd like to pour all new concrete sills but can't find any information on the type of cement to use? This are the questions I have.
Considering that the sills will be as little as 3/4" thick in spots.
1) What type of cement should I use? 2) Is there something I can add to speed up curing in this cold weather (Nights below zero) 3) Should I be adding fibre to re-enforce the cement? Where can I get it? Home Depot?
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HotRod wrote: ...

...
I haven't poured sills so can't really help there, sorry. The cold-weather pour "cure-all" is CaCl, of course, but the best bet would be to box in and have some space heaters to prevent freezing imo.
I'd just point out that if you're talking of a full-width sill, my experience w/ the manufactured stone sills wasn't a good one. Stone and concrete are pretty good conductors (as compared to wood) and while not having to paint is a nice feature, in a relatively humid location even w/o extreme cold winters they made a noticeable contribution to cooling in a room during cold weather and were especially troublesome with respect to condensation (to the point of having to replace trim and some framing around at least some of them owing to the water-induced rot. This occurred in a period of less than 15 years and also in locations w/ adequate slope, reasonable air circulation, etc. I wouldn't go back w/ a stone-like sill on a bet after that experience, personally. Also to me it seems like at least a partial waste of the (probably considerable) expense of installing energy efficient windows.
If were concerned about the longevity of replacing the sills with new wood sills, I'd suggest looking at the new manufactured lumber as an alternative.
IMO, YMMV, $0.02, etc., ... :)
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I'm specifically trying to stay with the look of some of the sills that are already on the house. Transfer of cold hasn't been an issue since there is an insulating layer between the sills and anything else. The sills butt up against the windows and don't travel through to the inside of the house.

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HotRod wrote:

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HotRod wrote:

<snip>
Never heard of it.

<snip>
A very poor way to go. If you want something characteristic of the the period of your house, go see a place that does stone counter tops. Odds are you'll find a stone material that can be sized the way you want it and won't look out of place. You might even get a deal with cut offs from Corian or some other counter material which generates a lot of waste for custom work. The advantages will be in price, looks and durability. HTH
Joe
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SORRY I now understand that I may have used the wrong word. The sills are on the exterior of the house. I'm not sure what the proper term would be for those. The sills on the inside of the house are thick old pine. Should I describe it as a window ledge?
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As an inspector for a large preservation district, I understand what you want, but I suggest against it right now. The water of hydration in the concrete is very vulnerable to freezing, but calcium chloride makes it less so, and using heaters to keep it from freezing could cause problems. Better IMO to wait till winter is over, and protect the new concrete from the drying effects of the sun. But some better alternatives to formed concrete could be considered while you await springtime.
HotRod wrote:

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Part of why I'm suggesting that you wait is that a lot of the window ledges were cut out of a slab of limestone, marble, whatever. If you put concrete into a form, you'll have little control of what the finished surface will look like, especially notable if you use aggregate of any real size. I do suggest you consider alternatives.
Michael B wrote:

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Every single window, 22 total, is a different size and depth etc. The window ledges that are there now are poured concrete sills, not ones that were pre-made. I think I'll probably wait until the spring but I still think this should be possible.

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Then the option of making your own becomes more attractive. Over the winter, you might check into things that would reduce the amount of water the finished ledge would take up, such as the use of acrylic additive in place of some of the water in the mix. Might be able to have the 3/4" part if you've managed to seriously reduce the freeze/thaw concerns by having a plastic component reducing its moisture permeability.
HotRod wrote:

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HotRod wrote:

...
OK, I understand the idea of trying to keep similarity to an original and since they don't protrude into the heated space the condensation issue raised earlier isn't likely to be an issue.
Can you post a picture or tow somewhere? Would undoubtedly be easier to discuss if could see a couple of what you have to try to match. Don't suppose there's one or two in disrepair that could be destructively investigated to see what/how the originals might have been done?
I'm assuming the were probably cast/poured in forms, then install rather than poured in place, but that should also be apparent from an inspection. I suppose though, that perhaps some of the apparent thickness problem(s) could be assuaged if they were in fact poured in place and actually they fill a cavity so only the visible edge is as thin as you may think the whole thing is...
I'd surely like to see one to speculate further. If they are truly poured and concrete and there's any area of size that is only 3/4" thick, they must have used a sand mix very high in cement. A small mesh screen could have been about the only reinforcement used in those days and if one uses a dry mix to avoid excess surface water, a good trowel job can leave a nice, slick surface that would likely hold up. I think the vinyl additives is not a bad idea, but in an application like this that doesn't have the load of a walkway or similar I don't think the thin profile is as much an issue as otherwise would be.
Just some semi-random thoughts...
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snipped-for-privacy@YourEmail.com says...

That doesn't sound like a candidate for concrete. AFAIK, 2" is minimum.

How about pouring them then let them cure inside? I still don't like the 3/4" thick part. My bet is they'll crack at the first freeze.

How about granite? They'll be expensive made to order but you might get some tailings from a custom counter shop or a statuary.
--
Keith

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After talking to a bunch of guys around town it turns out one of my cousins did this about ten years ago on his house, he lives about two hrs away but I've already arranged to head over to his house and get the details. He said that in spite of some colouring with age they look just as good as thiey did when he poured them in place. He also recommended waiting until the spring to start this project though. So I'll be doing research all winter :-)
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