[mx13]

I laid on a pretty thick coat of all-purpose mud on my ceiling a few days ago (my other thread about mixing and bubbles) and after sanding it just to restore it to flatness have a ton of bubbles that are up to 1/16" deep. Am I going to have to sand out that layer completely and start from scratch?

 

[ront02769]

No. Just thin your mud a bit and put a thin coat on.

 

[mx13]

I tried that this morning with some slightly thinned topping compound and it didn't fill the bubbles very well. I guess I was on the right track but need to thin it more.

 

[finisher65]

Just skim it a couple times or until the holes are filled.

 

[stick\shift]

There's no need to sand between coats of mud, just at the end. Big ridges and bumps can usually be knocked off with the knife, if needed.

 

[mx13]

Bubbles in the first coat were closed, or at least I thought some were. I was afraid that if I put another coat over that, I'd end up sanding back into some of those voids, or worse, having weak spots that would get cracked open later after painting if I didn't open them up with the sanding. Not a real concern?

Any hints on the consistency of mud for skimming into bubbles? As in how thick a layer will cling on a vertical knife, or cake batter, pancake batter, milkshake (which in my mind are progressively thinner)?

 

[Jaybee76]

I had the same question in the thread i just started. I see a constant mix of sand or not sand in between coats from advice.

If there isnt a reason to sand due to any bonding properties then sanding doesnt make a whole lot of sense between coats. Knocking off ridges and cleaning up the corners are probably what i will do.

I have some open bubbles like you mentioned. They should fill the next time. Im under the impression that mud is to flatten out the wall from taping the joints. As long as the last coat doesnt have them, I havent seen a good reason to go sanding back to scratch because of it. As long as it isnt a consistent issue throughout the whole project I dont see the reason to sand.

 

[jeffnc]

Im under the impression that mud is to flatten out the wall from taping the joints. As long as the last coat doesnt have them, I havent seen a good reason to go sanding back to scratch because of it. As long as it isnt a consistent issue throughout the whole project I dont see the reason to sand.

You can flatten tapered joints, but you can never flatten butt joints or corner joints. What you are trying to do with the first coat is provide strength to the joint. With the next 2 coats you're trying to hide the first coat by spreading it out so much it's not easily visible.


You will never be as good as the pros but it's not too difficult to avoid sanding until the 3rd coat, and keep that minimal. That is easily achievable.