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Old 03-27-2012, 03:32 AM
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craigchivers craigchivers is offline
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Mould on new plaster

Hi guys,
I've been of WC for some time and wanted to pop in for a question.
I've been making plaster sculptures for a long time but have recently developed a new peculiar problem. I'm sure it is climate related as I am now living in Tokyo and never had this problem in my Toronto, New York, or Rome studios. The problem is with mould developing on new plaster. The first time this happened the sculpture was still in the mold so I suspected that it had been left in the mold too long before taking it out. Simple enough, remove from mold as soon as possible. Recently the mould has attacked again. This time the sculpture was mould free once it was removed from the mold. There were some touch ups that needed to be done to the cast and as a couple of weeks had passed I routinely soaked it in water and proceeded to fix some small air bubbles etc. Then presto a week later there is mould that does not wash out on the cast. Tokyo has incredibly high humidity in the summer and is low in the winter. Today it is at 43% but i understand that this is relative humidity and not actual humidity. It certainly feels dry and my skin definitely tells me it's dry. The room where the sculpture was kept is a room I keep only for storage and it is not heated.
Anyone have any similar problems?
Cheers,
Craig
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Old 03-27-2012, 04:03 PM
sculpturedolls sculpturedolls is offline
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Re: Mould on new plaster

You aren't sealing it before it has a chance to dry out from soaking?

What about mold spores being in your actual mold and being transferred to the plaster and only growing with the introduction to the water.

I haven't had this problem with plaster. Have had mold in my clay though. The spores fly in the air when they are active so can jump to other things. Not a problem with clay as it burns real nicely in the kiln temps.

Wish I could be of help. Do you need to completely submerge your plaster cast when making repairs? What about just thoroughly dampening the area that needs to be repaired?
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Old 03-28-2012, 08:55 AM
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Re: Mould on new plaster

I don't work with plaster much at all - haven't in years - but the first thought that came to mind was a dehumdifier. Would that help? And cleaning the mold with Lysol between casts would kill any mold spores there. I suppose you'd need to wash it out to remove any residue after the Lysol dried. I don't know what Lysol would do to your mold or castings. Good luck with it!
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Old 03-30-2012, 10:51 PM
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Re: Mould on new plaster

Thanks guys,
Nothing is sealed. It's just a plaster cast. It was fine when it came out of the mold. I did touch-ups on it the following week and then several days later the mould appeared. I did some more touch ups on it the other day and the touched up areas have turned a yellowish colour! I have never had any of these problems before. It will certainly have to be painted to look uniform which is quite annoying. Some day I will have to track down a Japanese sculptor here to find out why these things have happened. I'm sure it's climate related, but as to why and how to avoid it seems a mystery.
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Old 03-31-2012, 02:44 PM
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Re: Mould on new plaster

The touched up areas turned yellow?? Wow, I don't know what would cause that unless it was a difference in humidity or how much water was in the mixture, or impurities in the water - here we have lots of iron in the water, so if you use unfiltered water in plaster, it can have a pinkish cast from the iron oxide. Let us know what you find out about it!
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Old 04-05-2012, 03:36 AM
sharry sharry is offline
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Re: Mould on new plaster

Don't know what's causing this unless your plaster has mould spores in it. I used to work with paper mache and rabbit skin glue, both of which went mouldy after a short while. To stop it I used a capful of a dettol type disinfectant when mixing the batch and this helped. I don't know if you're likely to get it reoccuring but it might be worth a try as it may kill any spores.
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Old 04-05-2012, 02:45 PM
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Re: Mould on new plaster

Sharry, your post reminded me of when I was doing papercasting. Sometimes the paper pulp would get moldy if I didn't use it up fast enough (it was in a covered bucket it came in from the factory, with liquid in there so it was ready to use). When it started to turn, I'd put a few drops of Clorox (bleach) in and stir it well. That usually did the trick and didn't change the brightness of the white paper pulp.

Dunno what bleach would do to plaster . . .
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Old 04-05-2012, 05:03 PM
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Re: Mould on new plaster

when mixing plaster, the water must be clean enough to drink. that being said, there can still be contaminats in the water. this could be from the source and within the building??

the plaster also could be carrying spores of mold. this could be the problem if the plaster has been exposed to the elements. does the plaster have little hard pieces of plaster within the powder? How old is the plaster? is must/should not be over 6 months old. the manufacture date should be on the bag.

what containers are you using to mix the plaster. are they clean of all dried plaster. what are you mixing the plaster with?

patching plaster. when you patch plaster, even using viscuous plaster from another, properly mixing batch, the plaster in the hole/defect whatever, dries at a super fast rate. you are putting the patch material against a raw, unsealed, highly absorbent material. this causes the liquid plaster to dry very fast. this patch plaster is more like a "Hydrostone" stone plaster. the patch material is harder than the 'kettle' or pottery plaster. it yellows or greys and if someone can get this patch to stay white, please let me know.

hope this helps-
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