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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, 2016 at 4:50
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    I use isopropyl alcohol spray it over the top before shutting it. I typically use 97% because I don't want to add more water than needed. I am sure 70% would work too. I always have a spray bottle with alcohol, use it for cleaning and disinfecting all the time. Honestly I mostly mix my own mud when needed, It gets faster and easier over time, i just keep a box to scrap out unused mud before it goes off. But when I do need remade mud i get rid of the plastic and just use alcohol. In a bind plastic works, even a plastic grocery bag helps.
    – Michael Mantion
    Jun 9, 2022 at 21:50

6 Answers 6

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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, 2016 at 17:14
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These are good ideas, but the best thing I have done is a combination of the the following: Make sure the mud is flat and there is no dried mud on the sides of the container, I use a large piece of bubble wrap that I put bubble side down after sprinkling the surface of the drywall with about 4 tablespoons of water, finally I use a single chlorine tab that you would put into a pool filter ( I leave the tab in the plastic bag that it came in, and just clip a corner of the bag to let the chlorine gas escape.) This process has allowed me to keep my five gallon drywall mud good for over a year. No drying out, and no mold at all.

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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, 2016 at 16:36
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    I wouldn't hesitate to give it a couple capfuls, but not so much that you substantially thin the compound.
    – isherwood
    Jan 12, 2016 at 16:38
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In my experience the mold is just on the surface. I skim it off with a spatula, add a small amount of chlorine laundry bleach (2-3 oz) with 2-3 drops of a Dove/Dawn dishwashing soap, mix it well, recover it and let it sit for 24 hours. I've never had a problem. In truth, mold spores are ubiquitous in this world and will grow anywhere under proper conditions, i.e. continually moist conditions. Cured dry joint compound does not fit that situation at all. If you want a mold spore free living condition you'll have to build a "bubble house".

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I poured a little vinegar into the container. It killed the mold, i.e., the black disappeared. This also adds moisture to the spackle which helps if it is a little dried out. Note that there is a chemical reaction (a few bubbles form) because vinegar is acidic and spackle is a base . However, this did not appear to degrade the spackle in any way. In fact the consistency of the spackle was much better after adding the vinegar. After pouring a little vinegar on top of the spackle and killing the mold growth, stir it into the remaining spackle to achieve and even consistency. Vinegar is a great mold killer.

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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, 2016 at 18:14

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