Why Does Drywall Mud Get Moldy? Let’s Fix It!

Mold in drywall mud, also known as joint compound, is a common issue that can render the material unworkable if it becomes too severe. Mold is a living organism that requires sustenance to survive, and joint compounds provide the necessary nutrients for mold to thrive. If a bucket of mud is not cleaned properly after use, or if it is not sealed correctly, the drywall mud can quickly become moldy.

Why Does Drywall Mud Get Moldy
Why Does Drywall Mud Get Moldy

The Consequences of Moldy Drywall Mud

Can Moldy Drywall Mud Be Used?

The usability of moldy drywall mud depends on the extent of the mold’s spread. If the mold has only begun to separate in the mud, it may be possible to remove the top layer of mud with a putty knife and continue using the rest. However, if the mold has spread extensively throughout the bucket, it is advisable to discard the mud and purchase a new bucket.

Should Moldy Drywall Mud Be Replaced?

While it may be possible to use moldy drywall mud by removing the top layer, it is generally recommended to replace the mud. Even if the mold has not heavily affected the mud, the quality of the mud will have deteriorated due to the presence of mold. Furthermore, drywall mud is relatively inexpensive, making replacement a cost-effective solution.

What Happens When Joint Compound Turns Brown, Green, or Black?

If you notice small spots in your bucket of mud that have turned brown, green, or black, there is a high likelihood that mold is present. These spots can grow over time, spreading throughout the mud and rendering it unusable. Moldy mud also emits a foul odor, similar to that of rotten eggs.

Preventing Mold Growth in Drywall Mud

How Long Does Drywall Mud Last After Opening?

The shelf life of drywall mud after opening is a subject of debate among experts. Some suggest that drywall mud can last up to nine months after opening, but others advise against storing used mud for extended periods due to the risk of mold growth. There have been instances where opened mud has become moldy within a month.

How to Kill Mold in Drywall Mud

There are several methods to kill mold in drywall mud, including the use of hydrogen peroxide, tea tree oil, vinegar, baking soda, and grapefruit seed extract. However, these methods can be expensive and may not restore the mud to its original quality. If the mold has only affected a small area, it may be possible to remove the moldy mud with a putty knife. If the mold has spread throughout the majority of the mud, it is best to discard the mud.

What Causes Mold Growth?

Mold is a living organism that requires food, water, and air to survive. In drywall mud, various organic materials can provide the necessary nutrients for mold. Other factors that contribute to mold growth include high humidity, improper cleaning of the bucket after use, and improper sealing of the bucket, which allows air to enter.

Can Drywall Mud Be Protected From Mold?

It is possible to protect drywall mud from mold, but preventative measures must be taken from the beginning. These measures include using dry compounds, isopropyl alcohol, bleach, chlorine tablets, and vinegar.

How to Keep Drywall Mud From Getting Moldy

Cleaning and Storing Drywall Mud

After completing a project, it is important to scrape off all dry compounds from the top, sides, and bottom of the bucket. The bucket should then be cleaned thoroughly before being used to store mud. A plastic bucket is recommended for storing mud, as it can protect the mud from various types of bugs.

Using Dry Compounds

If you are working with dry compounds, it is advisable not to wet all the compounds at once, as dry compounds have a lower chance of being affected by mold. Instead, prepare a small amount of compound at a time, and prepare more as needed.

Using Isopropyl Alcohol

Isopropyl alcohol can effectively protect against mold. After cleaning your bucket, spray isopropyl alcohol over the used mud, then seal the bucket cap properly. This method can provide long-lasting protection.

Using Bleach Powder

Bleach powder can slow down the process of mold growth. To use this method, seal the plastic bucket properly, then mix one tablespoon of bleach powder in one gallon of water. Soak a rag in the water, then wrap the rag over the bucket cap and secure it with a rope.

Using Chlorine Tablets

Chlorine tablets can also be effective for storing mud. After cleaning the mud bucket, place a chlorine tablet with a filter in the bucket, then seal the bucket cap. Make sure to clip a corner to allow chlorine gas to escape. This method is very effective and can help the mud last longer.

Using Vinegar

Vinegar can be useful for preventing mold growth, although it may slightly change the color of the mud. Pour a small amount of vinegar into the bucket, then seal the cap properly. The vinegar will kill the mold and extend the shelf life of the mud.


Mold can ruin your joint compound, but with a few extra steps, you can prevent this from happening. By understanding the causes of mold growth and taking appropriate preventative measures, you can ensure that your drywall mud remains mold-free and usable for your projects.

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