Why You Get Bubbles in Drywall Mud (and What To Do)


Drywall mud (compound) is used pretty much for any drywall repair job. For the most part, it is simple and effective to work with because of its easy application. However, there is a problem that does persist when it comes to drywall mud which is bubbles. These can be frustrating and tricky to remove, so let’s see how it’s done.

You get bubbles in drywall mud because it is a porous compound. This means that air is able to pass through it. In instances where the drywall cant absorb the air from the mud into the sheetrock, the air will be displaced through the mud—other examples of bubbles occur with drywall mud and tape due to varying temperatures and inadequate adhesion.

This article will briefly discuss what drywall mud (compound) is, and with that, we will take a look at the different kinds of bubbles that occur in drywall mud and why they occur. Then we will take a look at a detailed solution to solve the drywall bubble problem that plagues a lot of maintenance specialists.

Understanding drywall mud

In order to get a better understanding of why drywall mud acquires bubbles when the mud is applied to drywall, it will first be beneficial for us to understand what drywall mud is. Then we can understand why this phenomenon occurs.

Drywall mud is actually a type of joint compound used to strengthen and smooth over drywall and joints. There are two types; one comes in a powder form (dry) that you will mix yourself, and the other is pre-mixed mud. The latter will be bought ready-to-go, and you can start applying it instantly. There are various types of drywall mud that have different cure times (a set amount of time required for it to dry) and come with multiple fire ratings.

It s important to note that the fire rating for these products is tested as a system component as a whole and not as individual elements.

No matter which drywall compound (mud) you use, there is always a chance that it will bubble, and this is because the mud is mixed with water, and due to this, it is very porous in its nature (has gaps so air or water can seep through).

Why do you get bubbles in drywall mud?

There will be two main reasons you get bubbles in your drywall mud and the first reason is due to paint on the drywall, and then the other reason is due to the drywall tape. Let’s look at both these factors, explaining why they occur and then giving you workable solutions to solving this problem.

Bubbles over painted drywall

We initially said that drywall mud is porous and, additionally, so is drywall (sheetrock) itself. This means that it has tiny spaces that allow it to absorb air and water. Hence when drywall compound is spread over it, those little gaps (holes) in the sheetrock suck in the air of the drywall mud. This is why you constantly find that there will typically be no bubbles if you apply mud to clean drywall, which is excellent.

The problem comes in and persists when the drywall is painted. It is even more of a hassle depending on the paint and what type of finish it has (paint with a high gloss finish will typically cause the most problems). Due to the paint covering the drywall, the sheetrock loses its permeability (it is not porous anymore).

You have to remember that most paints are designed to be water-resistant and repel water. Imagine if the paint were not this way, then your house would need to have its inner wood beams replaced on a regular basis.

Due to the drywall not being able to soak up the mud now because of the paint, the air still needs to escape somewhere as the mud cures. The only other direction the air can now travel is in the opposite direction of the paint, which is why bubbles occur.

What to do with bubbles on drywall with paint

There is no easy workaround for this solution, and it will require some back and forth. There is usually no way you will be able to remove the bubbles by applying two coats of mud. The minimum number of coats it will typically take to remove bubbles on a drywall area with paint is three coats or more.

What you will have to do Is first is coat the applicable area with mud and give it a few passes as you usually would. Then check for bubbles on the sections with paint behind it. If you are fortunate and don’t find bubbles, you are lucky and continue, as usual; however, you will most likely find some on the areas with paint, so what you will have to do is skim the space tight.

This means you will use your knife or trowel at a 45-degree angle, and you will try and fill in any gaps, holes, or divets as well as trying to clear off the bubbles. You will do this by going over the area multiple times, skimming it as close to the drywall as possible. Furthermore, you will do this going in different directions, which include side to side and up and down.

Once this is complete, the wall may be nice and smooth; however, you may still see the joint on the area, which will be visible if you go ahead and let it cure and then proceed to paint it. This is not optimal, and the process of removing the bubbles is not yet done.

Once you have placed the initial coat and skimmed it as tightly as you can, you should then apply your next coat of mud. Depending on what compound you have, the curing time will be different. In some instances, it would be best to let the mud sit for approximately 3-5 minutes so as not to before placing your second coats so as not to disturb your initial coat that was tightly skimmed.

This coat will be applied how you usually apply a normal coat of compound, and you will do everything as usual, including feathering your edges. You will then conclude your second coat with a few finishing passes, and what you are trying to accomplish with this is trying to leave about 1/16 to 3/32 inches of mud on the drywall.

Next, you will leave the area to settle for approximately 3-5 minutes to see if any bubbles show up through the second coat. At this point, there should be no bubbles or very few left on the drywall. It is now that you let the compound cure and then lightly sand it down.

It is important to note that medium grit sandpaper should be used because you do not want to take too much off of the wall; otherwise, you may remove your hard work and have to start over. The point here is to gently sand away any bubbles if there are.

The last step is to apply the third coat of compound just like you applied the second coat. You will apply it as you usually do, moving through the areas with long passing strokes and feathering your edges, leaving approximately 1/16 inch of your final coat on top of the previous coats.

Once you have let the third coat sit for approximately 3-5 minutes, you should inspect the drywall and find no bubbles. You can then let it cure accordingly and move on to the next part of the renovation. If you would like a visual aid going over this process step by step, then make sure to check out this video here.

Bubbles over drywall tape

The next instance where you will notice bubbles is when using drywall tape. Drywall tape is used to hide the joints where the drywall sheets come together. Typically the procedure is for placing the tape on a drywall joint is straightforward.

You will initially fill up the joint going over the area with compound, applying it evenly and smoothly. You will then take a section of tape (you get two types that will affect bubbles and which we will discuss) applying it to the area with the joint. Taking your trowel, you will then go over the tape, pressing it firmly against the mud. After that, you will take another pass at the area with more compound sealing the tape and smoothing over any edges making the joined drywall area invisible.

As we said, there are two types of tape. The one variant is designed in a mesh type of structure which is great because this allows for the tape to adhere without making any bubbles. The next type of tape (paper tape) is solid, and this is the one you will typically have a problem with.

There are two reasons why this paper tape will not adhere to the initial underlying drywall compound, causing bubbles. The one reason is that it was never secure in the first place, and it simply peels away from the area. The other is due to temperature.

The temperature of the tape compared to the drywall becomes slightly different when the underlying mud and the overlaying compound start to cure. Due to this temperature change, it will eventually peel away from the drywall.

What to do with bubbles on drywall tape

In most cases, this is not a problem because if you applied the tape correctly, flattening it and pushing it into the initial coat of mud, there should only be a couple of ridges that should have peeled away from the wall along the edges of the tape causing bubbles.

Take note that no matter how many times you put a coat of compound on, this problem will persist, and you will have to deal with it in one of two ways.

If the area is large (approximately 2 feet or more), then it would be beneficial and in your best interest to remove that section of tape and start again. Again, make sure that your initial coat is not too thick and that after you have applied the tape over your seem, go over it with your trowel and push firmly, skimming it across the tape. You need to make sure that you embed the tape into the mud in this process.  Go over the area with your trowel with the wider edge skimming it nice and tight. After this is done, apply your top layer of compound over the tape. Take a look at this video here if you require a visual aid for this specific process.

At this point, the second problem may occur. This problem is where the tape pulls away from the wall, leaving only small ridges along the edge of the tape. If you find yourself with this problem, the solution is pretty straightforward. As long as the section of tape that has peeled away from the wall does not go over the seem (joint), all you would need to do is take a Xacto knife (utility knife) and cut out that section of the tape, leaving the rest intact. Gently peel away the section of tape that you have cut out.

You would then go over that area applying mud, filling up that gap. As long as the section you have cut out is not large, the compound should fill up the area nicely, and there will be no visible edges.

You may see a difference in color in the section where you removed the tape and filled it up with compound in some instances. You may also find that that area is slightly indented. You need not worry about this because when you do your second or third coat, it will cover that section up, and no discoloration or indentation of the area will be visible.

In cases where the tape peels away from the drywall along the seem, yet the section in question is still relatively small, you will again use your utility knife and cut out that section stopping at the point where the tape is firmly stuck to the drywall.  

Take note that if you leave sections of tape that are not adequately stuck to the seem, it may and most probably will crack over time. Hence, you will cut out that piece of tape with your utility knife, get another section of tape that is the same size as the area needed, and place it in that area as you would usually. Furthermore, this problem may occur at the edges of the drywall, but it can also happen at any area of the seam where the tape is not sticking correctly. The same principle of repair applies to all cases as long as the section in question is not too large.

If you require a visual aid in helping you understand what we detailed here, then take a look at this video where the repairs of drywall bubbles regarding tape are explained and repaired.

Final Thoughts

Understanding drywall mud is the first step in determining why bubbles occur in drywall compounds and how they can be resolved. We discovered that mud is porous, meaning that it allows air to move through it, and due to this, bubbles can form.

The first reason bubbles will form is if your drywall has a coat of paint on it, and the repair entails you coating said area of paint with mud. Due to the paint not being porous and the drywall not allowing the air to be absorbed, the air will be displaced through the mud, causing bubbles. The fix for this is to tightly skim each coat of mud, letting it cure and sanding it, repeating the process until the bubbles are gone.

The next form of bubbling with mud on drywalls occurs with drywall tape where the tape does not adhere to the seem of the adjoining drywalls correctly. This causes bubbles along the edges and also, in some instances, at the seem.

Depending on how large the section is in question that is bubbling, you will have to remove the entire length of tape and start again, or if the sections are small enough, then all you need to do is cut them out with your Xacto knife (utility knife). Following that, you will place another piece of tape in that section and pass over it with the drywall compound.

The last thing to note is that even though these may seem like straightforward repair jobs, you need to be careful because the pressure applied when trying to skim the mud against the drywall tightly could cause injury to your rotator cuffs. Keep vigilant, try to sand down painted areas first, and apply your tape correctly.

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