Gypsum Plaster mortar & grout

Quoted text begins.

Quoted text begins.Do you see plaster used in such a way in your restoration work?
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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!
End of quote.

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