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?
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
IMO, YMMV, $0.02, etc., ... :)
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.
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
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?
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.
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:
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.
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.
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
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...
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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