prattcm Posted January 8, 2016 Report Share Posted January 8, 2016 I've had a few bags of no 1 pottery plaster sitting in my garage for about a year. I'm in ohio so it been all sorts of temps, but it has been out of rain and hasn't been too humid. I tried mixing up a small cup of it and it didn't get completely smooth, it had small grainy looking pieces mixed throughout it. Is this normal? I have never worked with it? I poured some and let it harden, about a day later I took a look at it and it didn't seem as hard as I would expect it to be. I got it wet and could scratch away the surface pretty easily. I haven't worked with it before so again I'm not sure if this is normal. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted January 8, 2016 Report Share Posted January 8, 2016 Yes... plaster goes bad. Even sealed pretty well from humidity in a bin.... enough gets in that it slowly screw up. It can be "refreshed"... but such a cheap materials is likely not worth bothering. best, .................john Link to comment Share on other sites More sharing options...
oldlady Posted January 8, 2016 Report Share Posted January 8, 2016 john, please give details of refreshing old plaster. some of us are not necessarily cheap, just far away from a supplier. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted January 8, 2016 Report Share Posted January 8, 2016 Plaster takes a while to fully cure, and it can be quite soft and easily carved for a day or two (or three) depending on the humidity, how much water you used to mix it, etc. It can be a useful working property for making texture tools by carving. If it's kind of grainy like that, it'll be fine for reclaim slabs, stamps, slump and hump moulds and the like. It might not be suitable for slip casting moulds that require a uniform level of absorption throughout though. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted January 9, 2016 Report Share Posted January 9, 2016 ........ it didn't get completely smooth, it had small grainy looking pieces mixed throughout it. Is this normal? That's the giveaway as far as I am concerned. been there done that, bought the T-shirt. best, .....................john Link to comment Share on other sites More sharing options...
Mark C. Posted January 9, 2016 Report Share Posted January 9, 2016 What I have learned is you can sift the chunks out dry before mixing but the plaster still had moisture and its not going to give you good results. its cheap enough to only use new stock-You can keep it sealed in a container (air tight) and in a warm spot for some time when its new but once its exposed to atmosphere its only going to degrade. I would think the reclaim slab would work for old stock but how many of those does one need? I buy a new bag each time I need plaster no matter what the need If you are having trouble with this concept think of it like a dairy product-it goes bad over time and you just let it go and by more milk. Link to comment Share on other sites More sharing options...
Tyler Miller Posted January 9, 2016 Report Share Posted January 9, 2016 john, please give details of refreshing old plaster. some of us are not necessarily cheap, just far away from a supplier. You roast it. Not sure I'd use the oven for it (please no one roast plaster in their oven), but like 350F for a little while ought to do it. Plaster of Paris is roasted gypsum, mixing with water turns it back to gypsum, roasting it drives off the moisture again. That doesn't get rid of the chunks, which would need to be reground, but that's the process. Link to comment Share on other sites More sharing options...
Mark C. Posted January 9, 2016 Report Share Posted January 9, 2016 Tyler Roasting plaster sound right up my alley-My wife is going to love this when I try it in the oven. Oh ya I'll use my kiln. I even have some. Not sure after roasting and grinding and sieving it may be easier to by a new bag? Maybe a cost analysis is needed. I'm a little short on the grinder so I will need to make one.This is starting to sound like when I made my own clay I realized as I got older( like 23) that buying it was easier all the way around. Link to comment Share on other sites More sharing options...
glazenerd Posted January 9, 2016 Report Share Posted January 9, 2016 Had 2 bags of #1 that I let sit way too long before I tried to use them. I sieved out the lumps and clumps: even went a tad heavy on the water. It began flashing before I could even get it out of the bucket. The big lesson for me: do not inventory more than you plan of using in a short period of time. Nerd Link to comment Share on other sites More sharing options...
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