Why Does Drywall Mud Bubble? 12 Causes and What to Do
Don’t get stuck in the mud
Premixed mud is more likely to bubble than dry compound that you mix yourself.
Mix slowly and thoroughly to prevent pockets of dry powder and excess air.
Apply mud in a smooth “push-pull” motion with a drywall trowel or putty knife.
Wait at least 24 hours between coats of drywall mud.
Let your tap water sit for 30 to 60 minutes before mixing.
Mudding is tricky. Even experienced pros get bubbles from time to time. Luckily, there are some tweaks that can prevent drywall mud bubbles. Learn why your drywall mud bubbles and how to fix the issue.
If you want a good finish on your wall, it's absolutely worth it to pay for professional taping and mudding. Many DIYers are tempted to pay someone to hang the drywall and do the rest themselves, but this is one area where a skilled contractor can make a huge difference.
1. Using Premixed Mud
Premixed mud is convenient, but it’s harder to apply smoothly without bubbles. Sometimes there’s extra air in the mixture. And other times, bacteria, mold, or natural separation can cause bubbles.
How to Fix It
Use powder drywall compound, instead, and mix it with water on your own. Be sure to mix it following the manufacturer’s instructions.
2. Too Much Air in Mixture
Just like when you’re mixing pancake batter, excessive whipping and aggressive mixing can cause air bubbles in drywall mud.
How to Fix It
Slowly mix the compound into the water, adding more compound gradually. Use a low-speed mixer or paddle to blend it until all of the lumps are dissolved. Avoid creating a fast vortex while you mix because this can trap air. The mixture’s consistency should resemble smooth cake batter.
3. Not Mixing Completely
If the mud isn’t fully mixed, pockets of dry compound break the surface tension when you apply the mud to the wall.
How to Fix It
Mix the mud in smaller batches. Mix it thoroughly and slowly, without whipping in extra air. Your mixture should be smooth without any lumps.
4. Putting Tap Water in the Mix
Tap water contains dissolved gases from being in a pressurized water line. If you mix tap water right into the mud, it can create air bubbles that show up on the wall when you apply it.
How to Fix It
Pour your tap water into a bucket and let it sit for 30 to 60 minutes before mixing in the dry compound. You can also add a drop of dish soap to the mix to alleviate gas bubbles.
5. Not Enough Water
If your drywall mud mix doesn’t have enough water, it can lead to inconsistencies and bubbling when applying.
How to Fix It
Add a few drops of water to smooth out your mud. Apply the mud in a small area to gauge consistency and bubbles. Add extra water as needed until you get a smooth, bubble-free application.
6. Dust on the Wall
If there’s dust on the wall after sanding, it can cause the drywall mud to bubble up due to the uneven surface and air pockets forming.
How to Fix It
After sanding the wall, vacuum it from top to bottom with a shop vac. As an extra precaution, wipe the wall with a slightly damp cloth to remove any fine dust particles. Let the wall dry before applying mud.
7. Not Waiting Until the Previous Layer Is Dry
You should apply drywall mud in three thin layers, but it’s important to wait until the previous layer is 100% dry before adding the next coat. If the earlier layer is still wet, it can cause bubbling due to the extra moisture.
How to Fix It
Wait 24 hours between each layer of drywall mud to ensure it is fully dry. Or, follow the manufacturer’s guidelines for specific recommendations.
8. Mudding Over a Painted Surface
You can mud over a painted surface, but only if you prep it first. Mudding over a painted wall, especially one with an oil-based paint, can cause the moisture in the paint to be trapped underneath the fresh coat of mud, creating bubbles.
How to Fix It
Prime a painted wall before you mud over it. The primer seals the moisture and prevents the mud from bubbling.
9. Layers Are Too Thick
Applying thick layers of drywall mud can prevent a smooth finish and cause bubbles to pop up.
How to Fix It
Apply drywall mud in thin, smooth layers. Let each coat dry completely before adding another coat.
10. Pressing Too Hard
If you press your knife too hard while you apply the mud, the drywall tape can snap. Air bubbles can then develop on subsequent coats as the tape absorbs the moisture.
How to Fix It
Hold your knife at a low angle when spreading the mud. Push down gently but firmly to smooth the surface.
11. Not Using the Right Tools
The wrong type or size of tool can lead to trapped air and bubbling. You need to embed the mud into the tape properly, and that’s easiest with the right tools.
How to Fix It
Use a drywall trowel or taping knife, also called a putty knife, for applying drywall mud.
12. Not Using Smooth, Continuous Motions
Quick or inconsistent movements can cause air pockets. Drywall mudding takes precision and care to avoid bubbles.
How to Fix It
Use a smooth “push and pull” motion when spreading mud to push the mud into the crevices and embed the tape.
When to Call a Pro
Drywall mudding is particularly tricky and takes practice and talent to get it right. Hiring a professional is a wise investment that’s sure to give you a polished result with minimal frustration. Consider hiring a local drywall pro, and learn how to paint the room instead to save on costs. Hiring a drywaller to handle mudding costs $1.50 to $3 per square foot.
How to Prevent Drywall Mud Bubbling
You can minimize bubbling in drywall mud by following these tips:
Opt for dry powder instead of premixed mud.
Mix your mud slowly and thoroughly to prevent pockets of powder and excess air.
Let your tap water sit for 30 to 60 minutes before mixing in the powder.
Apply mud in three thin coats.
Spread mud in smooth, continuous strokes with a drywall trowel or putty knife.
Practice in inconspicuous areas before moving on to the center of the room.
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