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Mold and clay


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I have students with mold issues and as we know, clay has mold. I have always thought that the mold adds to the plasticity of the clay.  I am interested however in lowering the amount of mold in the studio to minimize our exposure and asking if anyone knows how to do that while maintaining clay plasticity. 

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Clay and mold go hand in hand. There's really no way to get rid of mold in clay other than mixing a fresh batch and using it right away. Making clay from scratch comes with its own health risks, though, so it's not recommended unless you have really good ventilation systems made for that kind of work. And mold will start to form on the clay within a week. It's a moist environment that's perfect for it. And yes, the aging process that grows mold also increases plasticity. If you've got slop buckets you could keep them covered, but you're never going to get rid of mold in the clay itself.

That said, I've been working in clay for 28 years, most of it in studios that have lots of students (universities, community studios, etc), and I've only experienced one person who said clay mold was an issue for them. I have mold allergies (started Flonase two weeks ago- it's early this year!), but clay has never been a problem.

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5 hours ago, Kay Yourist said:

Thanks for your input. I have been told that vinegar kills many molds and am considering adding some to the clay to see what happens. 

Regular store bought (3% -9%) Peroxide might be something to try. Vinegar is a bit overwhelming after awhile. Residence time is key, mold does not die quickly, it’s very tough.

Edited by Bill Kielb
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Peroxide is extremely good at killing both mold AND spores, it also degrades into water and oxygen and wont affect the chemistry of the clay.

How you would add this to the clay I have no idea.  I suppose you could spray it before it's used, or add some while pugging.  Most people are allergic to spores, so as long as the surfaces are taken care of it should be fine.  Spores require air to form, so the insides of the clay should not be allergenic 

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13 hours ago, Kay Yourist said:

Thanks for your input. I have been told that vinegar kills many molds and am considering adding some to the clay to see what happens. 

How would you add the vinegar?  Like when you are wedging?  I have allergies and I need to watch this stuff...I am unsure how to best to store the clay after I open the bag...

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1 hour ago, Meredith London said:

How do you use the peroxide?  

I don’t specifically use it as you intend but it is a pretty common safe oxidizing agent that is basically water which has use in killing mold so I thought I would suggest it to try instead or vinegar. Typical suggested procedure for surface mold cleanup with 3% is spray, let sit for 10 minutes or until it stops bubbling then scrub / wipe off. 

Not sure, this may help.......

Mold spores are everywhere and simply wait for the right conditions to grow. It’s nearly impossible to create a condition where no spores are present, they are everywhere and they are very tough and wait for the right conditions to grow in. There are many, many varieties so it’s not necessarily clay mold. It’s just a moist environment where that species will grow. So spraying surfaces could be effective in reducing the potential for growth for sure. Even end of the day or spraying slop / slip buckets may make a significant difference.

How could you tell / test? Usually pre tests over time and then maybe post tests all with counts of mold spores captured. Pretty hard to do though.

My sense and experience is: common sense diligent practice will help to minimize new mold growth which is likely your goal. As to stopping mold from getting in spaces, or on clay, is pretty much impossible. 

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  • 3 months later...

I reclaim all of my clay and I have a bucket for my slop when I throw.  I thought that mold in clay was ok and it fires fine, but my clay is full of mold.  The outside looks ok, but when I cut it the inside is full of mold and it smells when I cut it.  I have been thinking of throwing it away, but is there anything I can do to get rid of the mold?  Other then drying it out and rehydrating it with a water and bleach solution?

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  • 2 weeks later...
On 7/15/2021 at 10:27 PM, Half Baked Ceramics said:

I reclaim all of my clay and I have a bucket for my slop when I throw.  I thought that mold in clay was ok and it fires fine, but my clay is full of mold.  The outside looks ok, but when I cut it the inside is full of mold and it smells when I cut it.  I have been thinking of throwing it away, but is there anything I can do to get rid of the mold?  Other then drying it out and rehydrating it with a water and bleach solution?

Sorry this seems to have gotten missed!

It really is unnecessary. The mould won’t affect the fired piece or the kiln at all. This is completely normal for most reclaim, especially if you’re in a humid area. It is, unless you have very specific allergies, harmless. 

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