Drywall patching? - Paint Talk

city slicker · 02-08-2010, 07:35 PM

I was filling in some corner bead today on a previously painted 3 year house.

Using USG all purpose mud from Menards.

What causes bubbles in drywall mud? This is not my first job this has happened on. I have to sand once dry, sand and fill in the bubbles and hope more bubbles don't appear.

Rcon · 02-08-2010, 07:37 PM

Quote:

Originally Posted by city slicker

I was filling in some corner bead today on a previously painted 3 year house.

Using USG all purpose mud from Menards.

What causes bubbles in drywall mud? This is not my first job this has happened on. I have to sand once dry, sand and fill in the bubbles and hope more bubbles don't appear.

too much water in the mix or you've dried them too quickly (i.e. with a blow dryer). Could just be crappy mud.

**Workaholic** · 02-08-2010, 07:44 PM

If you are asking about the little bubbles that sometime show up on a joint after pulling a blade then it is usually air or water. Those type will sand out and the next coat will take care of it. Could be your mud.

If you are talking about a real bubble where it seems to just start blowing up and pushing off the surface then it is usually something on the wall causing an adhesion issue often film or oil of some sort.

city slicker · 02-08-2010, 07:44 PM

The mud is five months old and seemed really loose. I know it did not freeze because I store in inside.

city slicker · 02-08-2010, 07:46 PM

Yes, the tiny bubbles that appear as you draw the knife across it. Mud did appear watery.

Should the five gallon bucket be mixed-up again?

Wolfgang · 02-08-2010, 07:49 PM

Dont use old mud. Get some 20 min hot mud, mix it, apply it, tool it and you shouldnt have any bubbles. Oh yeah, use the easy sand stuff.

tedrin · 02-08-2010, 07:52 PM

Quote:

Originally Posted by city slicker

Yes, the tiny bubbles that appear as you draw the knife across it. Mud did appear watery.

Should the five gallon bucket be mixed-up again?

Could be porous drywall that was never sealed before .....Just don't press the knife down very hard and the bubbles will be reduced...Just go over the mud and smooth it out very lightly a few minutes after you apply it and you can reduce the bubbles even more..Expect to do a few coats of mudding and they will sand out..

ROOMINADAY · 02-08-2010, 08:43 PM

Unless I re-prime a wall, there are always air bubbles in premixed compound and some brands of fast set on a painted wall. The fast set 20 is an excellent suggestion as it hardens before the water has a chance to create havoc in your finish! You can also mix a little dish-soap in your mud to help break the surface tension and lessen the bubbles. When I am boxing mud, I put about 4 ounces in a pail and it leaves a smooth coat. I find a quick sand and tight skim in both directions will usually eliminate the bubbles with premix.

Builtmany · 02-08-2010, 10:14 PM

The bubbles happen to me mostly when I add water to my mud. I prefer to make it a little thinner then it is out of the bucket especially if the mud has sat around in heat for a while it's too thick for my taste. I imagine the bubbles are just air bubbles from my mixing. They are usually 99% gone after sanding and the final coat. If there are a few remaining we just use one time lightweight putty and prime over it without sanding a few minutes later.

Capt-sheetrock · 02-13-2010, 02:56 PM

Quote:

Originally Posted by Builtmany

The bubbles happen to me mostly when I add water to my mud. I prefer to make it a little thinner then it is out of the bucket especially if the mud has sat around in heat for a while it's too thick for my taste. I imagine the bubbles are just air bubbles from my mixing. They are usually 99% gone after sanding and the final coat. If there are a few remaining we just use one time lightweight putty and prime over it without sanding a few minutes later.

Guys, I know this is an old thread,,, but,,,, bubbles in mud????

There are two kinds,

1) caused by drilling the mud too much, ingesting air into the mix, like the kinds you see on cornerbeads in NEW construction

2) the kind described in this thread, once a wall is painted, its SEALED, if joint compound is "run" over this sealed process, the wall can no longer absorb the water from the mud. This is what causes the bubbles, its an "effervesance" effect. There is no way to prevent this, you CAN prime ahead of appying the mud, or you can just put a coat of mud on, then sand and re-apply mud. Eithr way will handle the problem.

The point is, there is no way (that I know of) to apply one coat of mud over an "old" wall system, and not have this problem.

When I re-do a wall in an older house, I skim the wall, then sand it, then skim again, cause after 30 yrs of trying, I KNOW these bubbles are coming, and I can't stop em.

wje · 02-13-2010, 03:20 PM

Quote:

Originally Posted by Capt-sheetrock

Guys, I know this is an old thread,,, but,,,, bubbles in mud????

There are two kinds,

1) caused by drilling the mud too much, ingesting air into the mix, like the kinds you see on cornerbeads in NEW construction

2) the kind described in this thread, once a wall is painted, its SEALED, if joint compound is "run" over this sealed process, the wall can no longer absorb the water from the mud. This is what causes the bubbles, its an "effervesance" effect. There is no way to prevent this, you CAN prime ahead of appying the mud, or you can just put a coat of mud on, then sand and re-apply mud. Eithr way will handle the problem.

The point is, there is no way (that I know of) to apply one coat of mud over an "old" wall system, and not have this problem.

When I re-do a wall in an older house, I skim the wall, then sand it, then skim again, cause after 30 yrs of trying, I KNOW these bubbles are coming, and I can't stop em.

You are absolutely right. When we do 2 foot drywall installation for insurance resto. companies, the mud only bubbles on the existing walls painted surface, and sets up normally on the new drywall. You will just want to lightly sand to pop the bubbles once before your final coat of mud so you can be sure to have them all filled for a perfect finish..