What is permanent?
I've found that stonework (usually 1.5 +/-" marble slabs) in lobbies in
NYC dating from the 1930's forward are often set with plaster. This with
ferric fasteners such as quite thin mild steel wire as a tie-back.
I'm not sure how long plaster has been in use but in reassembling a
Victorian Carrara marble fireplace breast in the oldest house in
Hartford, CT the original, and the replacement, were set with plaster.
You have to make sure to get a plaster that sets quickly enough but not
too quick. If it takes to long to set you have to sit and wait before
setting another stone.
Tempering does not seem to work for me.
I agree that you have to be very organized to work with plaster... but
then again it is incredibley flexible as a setting media.
On the above mentioned Hartford project I was swearing at the stones as
I set them and did not realize the docents, fine ladies, were standing
right behind me.
I talk to the stones when I play with them... sometimes it is fairly
intimate the discourse.
Plaster is absolutely NOT appropriate for an external or wet condition.
I've used dental plaster in the past but primarily for model & mold
making. I'd not consider it for stone setting... but I am willing to
experiment.

GO

Simon Brown wrote:

>>>Do you see plaster used in such a way in your restoration work?
>>>
>>>
>>Would the use of plaster be considered to be a permanent material to
>>assemble stone work?
>>Have you seen plaster used in outdoor locations? I think not, but I might as
>>well ask.
>>Lastly, I though plaster would set up to fast to do such work, but maybe I
>>don't think fast enough!
>>
>>
>
>George,
>
>Gypsum plaster (Plaster of Paris) is used for traditional setting of stone,
>in combination with non-ferric fixings. It shouldn't be used anywhere it
>could be wetted repeatedly, or is will swell and dissolve. I once replaced
>panels in a shopfront that were fixed with plaster and copper, there was a
>leaking downpipe behind them that caused the wetted plaster to push the
>slabs off the wall.
>
>Plaster is also useful for temporarily fixing stone in place, like supporting
>stone blocks under a slabbing saw or polishing machine, or holding a stair
>riser in place so the tread can be solidly bedded on top of it.
>
>There are a few different types of plaster availble here, I often use Dental
>Plaster (pure Plaster of Paris) because it has a setting time of 3 minutes, or
>Casting Plaster which takes a little longer to set because it has a retardant
>included. I mix plaster with Type A Portland cement in equal parts just to eke
>it out a little. When I wash my tools in water, the water gets contaminated with
>set plaster. If I want the plaster to set faster, I use the dirty water to mix
>fresh plater, otherwise clean mixing water is important. You have to be very
>organised to use plaster- yes, it does go off quickly!
>
>Simon
>
>
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