Why Does Drywall Mud Mold? Can You Stop It or Use It?

If you have ever hung drywall in your home, you likely had some drywall mud left over after the job.

You probably stored the remaining joint compound in your shed or garage, only to open the lid a few weeks later and find fuzzy black mold.

Mold growth is very common in drywall mud, but why does it happen?

Drywall mud will develop mold after exposure to air due to its moisture content. The ingredients in drywall mud include minerals, such as limestone and talc, mixed with water to form a damp paste. This moisture causes mold and mildew in the drywall mud if it is not stored properly once opened.

If the drywall mud dries out, it becomes unusable, even if you add water.

In addition to storing leftover joint compound correctly, it is also important to pay attention to the expiration date on the container.

Drywall mud has a limited shelf life, especially after being opened.

Read on to learn how to prevent moldy drywall mud and whether or not it is still usable.

why does drywall mud mold

How Do You Prevent Mold on Drywall Compound?

The key to preventing mold in drywall mud is to ensure any air bubbles are removed before storing it for an extended time.

To get rid of air bubbles, firmly press the joint compound into the bucket and smooth the surface.

Add a couple of inches of water to the top of the drywall mud to keep it from drying out.

Be sure to use clean water to prevent adding bacteria to the mud.

Pour this water off before using the drywall mud again.

To ensure a proper seal, place a piece of plastic wrap over the top of the airtight container before replacing the lid.

If you are having difficulty getting the lid to close tightly, use a rubber mallet to tap the edges of the lid down.

There will be an audible click when the lid is closed correctly.

Keep the container away from direct sunlight and store it at 55-95° degrees Fahrenheit (35° C).

Extreme temperatures or exposure to sunlight will cause the organic materials in drywall mud to degrade quickly.

Do not allow the joint compound to freeze, as this will cause the mud to dry out and harden.

Even if you add water to the dry mud, you will not be able to use it.

Pre-mixed drywall mud is usually sold in buckets ranging from 1 to 4.5 gallons, making it easy to buy only what you need so there is less product left over.

It is also essential to keep your tools as clean as possible when using drywall mud.

Any bacteria introduced into the drywall mud will increase the chance of fungal growth and speed up the expiration time.

Can I Use Drywall Mud That Has Mold In It?

If your drywall mud only has a layer of mold spots on the surface, you may be able to use it again.

You will have to remove the mold layer before using the drywall mud, but if the problem is not severe, it will not be much of an issue.

However, if mold spores are growing several inches below the surface of the joint compound, you will need to throw it out.

When the fungus has spread throughout the drywall mud, there is no way to ensure all of the spores are completely removed.

Using moldy drywall mud is not a good idea because you will be spreading the fungal spores all over your walls, which may cause you many problems later on.

Fortunately, drywall mud is relatively inexpensive, so it is not difficult to replace.

Always buy the smallest amount of drywall mud you need for your job to prevent having any leftover.

Plan to use one gallon of drywall mud for every 100 to 200′ square feet of drywall.

If you live in a humid environment, you may want to consider purchasing a mold-resistant joint compound.

Mold-resistant drywall mud is a little more expensive, but it will reduce the risk of mold growth both in the unused product and your walls.

How Do You Get Rid of Mold on Joint Compound?

If there is surface mold on your drywall mud, use a mud knife to scrape the moldy layer off carefully.

Use a paper towel to remove any mud from the sides of the bucket, as it may contain fungal spores.

Thoroughly clean the mud knife after scraping the mold away to avoid accidentally contaminating the rest of the drywall mud.

Assess the rest of the joint compound to see if there is more mold underneath the surface.

It is probably safe to use if the drywall mud looks clean, but there is no guarantee that the mud is free of mold spores.

While vinegar and bleach are commonly used to remove black mold from various surfaces, do not add these cleaners to your drywall mud.

Adding vinegar or bleach to your drywall mud may change the consistency too much for the mud to remain usable.

Even if you clean the joint compound, you may still have moldy walls, especially if you live in a humid climate.

When the mold is dispersed throughout the drywall mud, there is no way to clean it, and you will have to dispose of it.

Since the joint compound is cheap to replace, most experts recommend throwing it out if there is any mold, even if it is just on the surface.

Learn if drywall mud sticks to concrete and what to use instead.

What Does Bad Drywall Mud Smell Like?

Although some say it smells like chalk, fresh drywall mud does not have a distinct odor.

Once a joint compound has surpassed its expiration date or has not been stored in the proper conditions, it develops an extremely foul smell.

Most people compare the odor of bad drywall mud to roadkill or rotten eggs.

This foul smell is caused by bacterial growth as the organic materials in the drywall mud break down.

If you open your bucket of drywall mud and it has a horrible smell, absolutely do not use it.

Not only will the expired joint compound be ineffective, but you will be spreading the awful smell on your walls.

With proper storage conditions, drywall mud has a shelf life of around nine months from the manufacturer’s date.

There is usually an expiration date on the bucket of drywall mud, and it is best not to use it beyond this time, even under ideal conditions.