# Moon craters



## Jmayspaint (May 4, 2013)

I'm sure you drywall guys/gals are tired of hearing this question, and I don't think there is really any one answer, but I'm hoping someone can help me out. 

Lately I've been working with and after a new (to me) drywall guy. He does pretty good work, even though he's kinda old fashioned and low tech. But lately I have been seeing crazy amounts of moon craters (air holes) in his skimming. Today I'm priming out a house where he skimmed over oil primer and they are everywhere and some of them are really big and deep. 

He uses green lid all purpose mud, and trowels it on. I don't think he stirs the mud with a whisk, just his knife or a stick. And I don't think he thins it much. 

Any ideas why these are so bad? Some places look like the mud was maybe too thick, but idk.


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## nismo972 (Sep 23, 2013)

I always have to add water to the premix green lid mud. But some times I get those too.

Sent from my SM-S765C using diychatroom.com mobile app


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## jeffnc (Apr 1, 2011)

I've never really nailed down exactly when it happens. Obviously if you whip a relatively dry compound too much it can happen, but sounds like he didn't do that. It happens sometimes I don't expect. If I mix in a little water to make the compound a little creamier, it seems less likely to happen.


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## ToolSeeker (Sep 19, 2012)

With out a mixer he's not getting it stirred enough to get it creamy, it does need to be thinned. Between a pint and a quart depending on what your using it for. But if your skim coating the ultra light weight is a good choice. It's thinner and easier to pull and easier to sand.

I wouldn't use the ultra to tape with it has no strength. But it's good for skimming and final coat. Somebody may say add dish soap but that's only good for fish eyes wouldn't work for craters.


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## Stubbie (Jan 7, 2007)

His knife angle is way to steep. He needs to run a shallow angle with a 10" knife pressing harder than when doing a bedding coat..


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## jeffnc (Apr 1, 2011)

How could the width of his knife be related to this problem?


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## Stubbie (Jan 7, 2007)

jeffnc said:


> How could the width of his knife be related to this problem?


 Jeff this time you have misread the intent because you have no idea what knifes widths are used for different coats of drywall. I was simply stating that you would use a 10" knife or longer maybe even a 12 " the problem is how he is using it. It seemed clear to me based on the first sentence ...


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## oldrivers (May 2, 2009)

he must be putting it on to heavy for a 1 time skim coat . he either needs to put it on tighter or apply a tighter 2nd coat . skim coating you want a fairly wet mud more like mayonnaise almost and not peanut butter .


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## Jmayspaint (May 4, 2013)

Thanks guys, It seems like mystery when and why these things happen. This job just seemed extra, extra, bad. I wasn't there during most of the skimming, but was told that it got three coats. One coat setting and two finish. 

I'm thinking to suggest thinning the mud a little (they don't now at all), and mixing the mud more. 

Am I wrong in thinking that skim coating on the scale of a whole house with ten foot ceilings should be done by rolling on the mud and using a wide squeegee? Or is that just a matter of preference.


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## Stubbie (Jan 7, 2007)

I think I would wonder why he let all that cratering slide. I think the bottom line is you need to make a friendly approach as to this quality of work not being acceptable.


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## Jmayspaint (May 4, 2013)

Stubbie said:


> I think I would wonder why he let all that cratering slide. I think the bottom line is you need to make a friendly approach as to this quality of work not being acceptable.



Yeah, that's what I'm thinking. I wish I could make a suggestion or something. The skim was nice and tight, but I've painted behind enough Drywallers to know something had went wrong here, the cratering was way worse than normal.


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## jeffnc (Apr 1, 2011)

Stubbie said:


> Jeff this time you have misread the intent because you have no idea what knifes widths are used for different coats of drywall. I was simply stating that you would use a 10" knife or longer maybe even a 12 " the problem is how he is using it. It seemed clear to me based on the first sentence ...


Uh, no, I have a very good idea what widths are used for which coats and applications. I probably own 10 different widths myself. The width of the knife has nothing to do with cratering effects, but since you brought it up, if he's skimming a wall, 10" is probably a bad knife choice. And no, you didn't say 10" or even longer, you said 10". And it could be a mile long, it wouldn't fix this problem.


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## Stubbie (Jan 7, 2007)

jeffnc said:


> Uh, no, I have a very good idea what widths are used for which coats and applications. I probably own 10 different widths myself. The width of the knife has nothing to do with cratering effects, but since you brought it up, if he's skimming a wall, 10" is probably a bad knife choice. And no, you didn't say 10" or even longer, you said 10". And it could be a mile long, it wouldn't fix this problem.


I gave my opinion Jeff sorry your melting down about it.


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## jeffnc (Apr 1, 2011)

Stubbie said:


> I gave my opinion Jeff sorry your melting down about it.


I'm fine. I gave you the benefit of the doubt - just in case I was wrong - by asking you how knife width could cause or contribute to this problem. Instead of giving a reason, you used the opportunity instead to insult my knowledge and experience. So at this point I'm going to assume there is no reason for your comment about 10" knives, and I'm just letting the listeners know - the size of knife has nothing to do with cratering effects. Switching to a 10" knife will not help you.

Also, if in fact we're doing skim coating, a 10" knife is probably not the best choice anyway. In my opinion, a 14" squeegee such as the Magic Trowel is better than metal, and better than a shorter knife. This is what I use.

http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH10MAY_SKICOA_04.JPG

So, you are entitled to your opinion, but I disagree, and apparently you didn't have a reason for your opinion anyway. So everything is fine now.


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## ToolSeeker (Sep 19, 2012)

JMay you are correct the finish coat should be thin and a squeegee to take it off. In fact it can be thin enough to put on with a paint roller. The purpose of the final coat is to fill the small imperfections. Almost all of what you put on you pull back off.

Personally I like the new Ultra lightweight mud in the bucket with the ugly green lid. It's thin and easy to work with and has very little glue in it so it's not good for taping but as a topping it works easy, and sands easy. Again this is just a personal preference.

I use a 16" trowel for my final skim but if you like the squeegee method SW sells one called a Magic Trowel it's a little stiffer than a regular one.
Hope this helps.


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## Stubbie (Jan 7, 2007)

jeffnc said:


> I'm fine. I gave you the benefit of the doubt - just in case I was wrong - by asking you how knife width could cause or contribute to this problem. Instead of giving a reason, you used the opportunity instead to insult my knowledge and experience. So at this point I'm going to assume there is no reason for your comment about 10" knives, and I'm just letting the listeners know - the size of knife has nothing to do with cratering effects. Switching to a 10" knife will not help you.
> 
> Also, if in fact we're doing skim coating, a 10" knife is probably not the best choice anyway. In my opinion, a 14" squeegee such as the Magic Trowel is better than metal, and better than a shorter knife. This is what I use.
> 
> ...


Jeff I will offer my apologies for an inappropriate comment .. that was stupid on my part. I'm sorry you think I said a knife width is why the skin coat cratered. I don't think anyone else took it that way.


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