SB: Re: Window sills

[Robert W Tom <archilogic@juno.com>]

on Sat, 14 Apr 2001  Charmaine R Taylor <> wrote:

>in addition, a Tufastone type material, which is sand peat moss and
>cement can be cast in place too ( I haven't done it yet on sills tho)
>and you can achieve an old stone look , plus shape the edges smooth or
>rough, color the sills etc. 

An interesting idea. 

Although I've read about Hypertufa and Tufastone, I've never actually
cast anything out of the material so I don't know anything about its
suitability for window sills.

What I do know though, is that peat moss soaks up and hangs onto water
and I'm *guessing* that this property would not change when it is used in
a concrete mix ? (Perhaps this is why Hypertufa  is used extensively to
make garden planters... for the same reason that terra cotta pots are
preferable to plastic pots)

If  in fact Hypertufa & Tufastone are relatively pervious and tend to
soak up and hang onto water, then this may not be a Good Thing in wet and
cold climates .

WRT the "wet" part, any cellulosic material (ie wood, straw) in
prolongued contact with the material would be prone to rot if for some
reason an adequate moisture barrier were not provided or failed to do its
job.

WRT the "cold" part, freezing of the moisture within the Tufastone would
likely cause spalling and/or cracking and ultimately self-destruction of
the material, not to mention potential rotting of the material for which
the sill was supposed to shed water and protect ... unless the addition
of the peat material to the mix somehow creates voids in the concrete
similar to the manner of air-entraining agents .

These are items that should be thoroughly investigated before one goes
ahead and makes all of one's exterior window sills out Hypertufa or
Tufastone. Poorly detailed or inappropriate window sills are the cause of
many wet wall problems in building systems of all sorts and SB walls are
especially vulnerable.  But y'all already knew that . Right ?

Perhaps a "natural" material that could be considered for window sills is
slate.
Here in Ottawa, at Cohen's ( a demolition/salvage joint) they've been
known to have big sheets of 3/4" (or thicker) in sizes ranging up to 5' x
8' , selling for I think something like $2.50 per square foot. (They also
had big sheets of 1.25" thick Carerra marble (bathroom stall partitions I
think) for about $5 psf but no one would use something as ostentatious as
Carerra marble for window sills on a SB house. Right ?)

They were originally school chalk boards. (I've contemplated buying some
to make a billiards table for when I reach old age and will have nothing
better to do than fleece old geezers of their pension cheques.)

Slate cuts easily with an abrasive blade in a circular saw and corners
can be rounded over with a carborundum stone mounted on an angle grinder.

It is certainly suitable for window sills as it is a traditionally used
for that purpose in places like Indiana and Vermont where slate is
quarried and as we all know, slate-shingled roofs provide service for
periods measured in centuries rather than years. The large size of the
chalkboards would enable one to cut pieces that would do the entire sill
of even the widest windows, without any joints which could provide a
route for water to get into the bales below.

                 ===    *     ===
Robert  W. Tom          Kanata, Ontario, Canada       
Rob_Tom@ErehwonDesignGroup.intranets.com 

please visit:  http://www.theHungerSite.com daily
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