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when will it dry off plaster bat?

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Never used plaster of paris before, but I made some posh plaster bats using proper potters' plaster they're and inch and a half thick and about 15" wide, threw a platter on one a week after I made it and at least a fortnight later still waiting for it to "pop off".

It has been damp and cold here, I've put the whole thing into boiler cupboard for occasional hour (until plaster was nice and warm) and even on top of the kiln for a bit too.

Clay is still only leather hard, about right for scraffito decorating.

In desperation I did try running a wire underneath but it's too hard for that now.

Just keep waiting?

Don't laugh if I've done it wrong!

 

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Edited by oly

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Was the plaster bat totally dry before making the pot on it? It can take more than a week for the plaster to dry if the weather is cold and damp. In my experience a slab that thick would not totally dry within a week unless it was in a room with a dehumidifier, or in a drying box. If the bat wasn't dry, then it can't absorb the water out of the clay.

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Did your plaster bats have time to dry before being used?  I’ve only used regular plaster from the hardware store for bats & never had that issue but I made a Mold with potters plaster & had problems waiting for the poured clay to pull off.  It seemed the plaster had trouble absorbing enough of the moisture.  Make sure when using plaster you don’t put any down the drain.

joy

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27 minutes ago, neilestrick said:

Was the plaster bat totally dry before making the pot on it? It can take more than a week for the plaster to dry if the weather is cold and damp. In my experience a slab that thick would not totally dry within a week unless it was in a room with a dehumidifier, or in a drying box. If the bat wasn't dry, then it can't absorb the water out of the clay.

Neil, this is what i'm wondering now, if the bat was actually dry when I started using it.  The weather's a bit better now but it was very damp and cold for some time (typical England!)

 

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29 minutes ago, Joy pots said:

Did your plaster bats have time to dry before being used?  I’ve only used regular plaster from the hardware store for bats & never had that issue but I made a Mold with potters plaster & had problems waiting for the poured clay to pull off.  It seemed the plaster had trouble absorbing enough of the moisture.  Make sure when using plaster you don’t put any down the drain.

joy

I think the potter's plaster might be extra fine,  I'm not sure of the difference tbh.

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It is extremely humid here in Mississippi. Except today it is only 24%, but the ground is still oozing water from all the rain lately.

Although I have been told time and again no need to wire off, BUT when throwing on a plaster bat(potters plaster), I always use the cutoff wire right after throwing the piece. Then place the bat on a wire shelf that is laying on a plywood shelf. About 12-18 hours later the piece usually "pops off". If I don't wire off right after throwing it can be up to 2 days before it "pops off".  Each location is unique... 

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#Oly.   I'm not surprised it hasn't popped off yet.  One week for the plaster to dry this time of year, even in an airing cupboard may not be enough.  I usually put a fan in front of plaster moulds to help them dry.  And large, but thin slip-castings can take days in a centrally heated studio before they shrink enough to remove.

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47 minutes ago, Min said:

Looks like there is some plaster film stuck to the clay. I would toss the trimmings that have plaster on them. Glad it worked! 

Yes you are right, I have thrown them away :)

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My guess is you did NOT dry the plaster out well before using it. You should never wire plaster and clay.Just looking at the plaster sticking to your pot bottom tells me it was not dry.

Now dry the plaster out until it in bone dry. Pots dry fast on dry plaster and can pop right off in day and without ant plaster residue on them.

Edited by Mark C.

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51 minutes ago, Mark C. said:

My guess is you did NOT dry the plaster out well before using it. You should never wire plaster and clay.Just looking at the plaster sticking to your pot bottom tells me it was not dry.

Now dry the plaster out until it in bone dry. Pots dry fast on fry plaster and can pop right off in day and without ant plaster residue on them.

Yes I'm sure you're right, a combination of inexperience using plaster and the very cold damp weather – the gods were against me.  Thankfully, I've got through it and know a bit more now :)

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Great work!  Please include a picture of the glaze  fired piece so we can see the vibrancy of the underglazes that you chose.  Someone will  be very pleased to have that piece.

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I KNOW THAT DOG!   his name was Spooky.  he was a mix of bedlington terrier and some kind of coarse haired big, black dog.  the black hair stuck straight out and the lighter curly stuff surrounded the black ones.  he looked like a ghost so his name fit him well.  :D

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