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Joint compound comes in larger containers than I need. I have had this problem for years where storing opened but unused joint compound leads to mold growth, usually starting within a week or two. I'd like this to not happen, or at least extend it to months or years, so I don't need to keep throwing away 95% full containers and buying new ones.

The only thing I've really tried is storing it in the fridge after opening. This has inconsistent and limited effect.

On rare occasions I have been able to store it for extended periods of time with no mold growth but I was never able to determine how I did that, and upon opening and reclosing those particular containers mold started to grow anyways.

So, my question is, how can I make unused joint compound last longer?

  • Are there precautions I can take during use to reduce contamination?
  • Are there ways I can store it to reduce growth?
  • Are there mold killing additives that won't affect its usefulness?
  • Are there certain brands or types I can look for that are less prone to mold growth?

Often any molds that grow seem to be mostly in the surface, the joint compound underneath usually seems clean, but I never really want to deal with that mess.

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If you're using a really small quantity every once in a while, have you considered the powdered versions? You can get long cure like 90 minute or scary fast like 5. It really isn't a big deal to hand-mix a batch. – Aloysius Defenestrate Jan 13 at 4:50
up vote 5 down vote accepted

Mold grows on any surface that provides food for growth. Joint compound contains organic compounds and lots of moisture. The compound will only last a finite length of time even under "ideal" conditions (if mold spores don't ruin it drying-out will).

To slow down its' expiration time: when storing the compound for any length of time, place the plastic that was included with the compound so it completely covers the top layer. Next, soak a rag in a mixture of 1 gallon water to 1 tablespoon of bleach. Wring it out and place it on top of the plastic. If the lid for the bucket doesn't have a rubber seal place a plastic trash bag on the rim of the bucket and seal tightly with a mallet.

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This may be a better solution, and would help prevent dryout. The drawback is that you have to deal with the rag each time you use the product. – isherwood Jan 12 at 17:14

Mix in a bit of chlorine bleach. It won't affect the compound and the odor dissipates fairly quickly upon use.

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Good idea. What do you think a good ratio is? I'm looking at a 3lb container right now and my gut says about half a cap full of bleach. – Jason C Jan 12 at 16:36
I wouldn't hesitate to give it a couple capfuls, but not so much that you substantially thin the compound. – isherwood Jan 12 at 16:38

Joint compound needs air to grow mold.

So before you are putting lid on, flatten the compound surface level and then add a couple inches of water, then put on lid.

Also if you have mold in your compound just throw it away. Would you want moldy materials put in your house?

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I do throw it away. That's the problem! :) – Jason C Jan 12 at 18:14

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