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Joint compound...what am I doing wrong??


mossman's Avatar
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01-18-12, 10:01 AM   #1  
Joint compound...what am I doing wrong??

I have a general question regarding the application of joint compound. Supposedly, I shouldn't have to sand until the very end (3rd coat), but I always seem to need to sand after the second application because of tool marks, ridges, etc. I just can't seem to apply the mud smooth enough. What am I doing wrong? Can someone give me some general tips/advice/techniques for applying the different coats (for example, how thick should the consistency be, should I apply mud in small strokes where it is needed then go back over the area with long strokes, etc.)?

 
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01-18-12, 10:13 AM   #2  
If you could watch a pro for a day you would pick up soo much. The ones I have worked with always used long strokes, but that takes practice and the right mix. IMO, if you have a fine line left from the tool edge, you don't have to chase it and make it perfect. The standard mud is soft enough that a quick once over with your dry blade and it's gone and ready for the next coat. Chasing small imperfections often leads to more imperfections.

I'll watch to see what the real pros have to say.

Bud

 
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01-18-12, 10:23 AM   #3  
I don't have the skill level to only sand after the third coat, either. A lot of times, though, you can use the knife to knock down ridges or high spots instead of having to sand them.

 
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01-18-12, 10:28 AM   #4  
If not sanding until the very end is a matter of skill, then I can accept that and don't feel so bad having to sand after the second application. I understand how to knock off any ridges, etc with a dry knife (once mud is dry), but some areas just need sanding in my opinion before I put on the final coat, otherwise I feel like I could just keep piling on more and more mud trying to cover the imperfections, which would make sanding even more of a nightmare.

 
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01-18-12, 10:48 AM   #5  
Yeah, sometimes the choices are to sand or feather out further and there's a limit on the feathering.

 
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01-18-12, 02:13 PM   #6  
It also helps to thin the j/c a little, I wish I knew how much water to tell you to add I just add and mix until it looks/feels right.


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01-18-12, 02:30 PM   #7  
I'm not a pro at it either but I'm a lot better than I used to be. The biggest thing I have learned is to try and do one thing at a time... and give stuff time to dry before you drag through it again- like do all your "belly bands" first. By the time you get to the end of them, the first ones will be setting up enough that you can go back and do one side of all the wall angles (I'm trying to avoid dragging my knife through any wet mud here). Once they are all done you can coat any butt joints... and then if the one side of the angle is dry enough, go back and do the other side of the wall angle. This seems to work better than trying to do belly band, butt joints and angles all at the same time in a small area.

This would obviously be different than a pro, because he would probably be using corner boxes and flat boxes which do a lot nicer job and they just leave touchups on each end of the boxwork.

I'll try to apply a generous amount of mud (but not TOO much) and then I'll make several long swipes to spread it out thinly and evenly, scraping off any excess in the process. When you coat the sides of a joint, keep pressure on the "outside half" of the knife (not really tipping it, but kind of) so that the outer edges of the joint are perfectly tapered down to nothing. This will leave nice clean edges on your outer perimeters.

As mentioned, when the mud is dry you can lightly scrape all the dry bits and ridges off instead of sanding. A skim coat prior to final sanding will usually fill in those voids. After sanding, using a 300 watt bulb and a clip-on cage light will help you spot any shadows or ridges that need to be touched up once more. IMO, it's best to circle these touchup so that you can spot them when you do your final sanding.

The only time I thin the mud is when I'm taping. If it's really hot or something I might add a "little" but it would be very little. Adding water makes it creamier and easier to apply, but the drawback is that it will take a little longer to dry and it will also shrink back more.

For small jobs I will use the dry mix (Sheetrock lightweight setting-type joint compound) like "easy sand 20" or 45 or 90. the 5 minute stuff is for very small repairs- it sets up FAST! The nice thing about it is you can mix up as much as you need, and it speeds up the dry time so that you can recoat it faster.

 
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01-19-12, 07:10 AM   #8  
The second coat went on easier than I anticipated. It is looking pretty good at this point. Several minor ridges, tool marks, etc, but sanding will take care of that. So I'm assuming my next coat (3rd coat) is my final coat (also called "skim" coat). Should I thin out the mud more for this coat or just apply less product and concentrate more on feathering? In other words should I use the same consistency for all three coats or do I change the consistency for a given coat? I've heard that thinning out the mud for the tape coat is common, but I am not sure about the other two coats.

 
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01-19-12, 07:21 AM   #9  
What size knives are you using? You should be using at least a 10 inch knife for coating these patches. I know you said these patches were small but a larger knife will not leave tool marks. On the final coat test to see how flat your finish job is. Take your knife and put it edge side on the ceiling and see if it rocks back and forth or there is and indentation or its flat. If it's flat just put a final skim on to fill in any voids and improfections. If it's not flat you may have a little more work to do. 3 coats is a general rule but you may need more.

 
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01-19-12, 09:10 AM   #10  
I almost always thin my mud a little, just enough to make it 'flow' better. When time permits, I'd rather apply an extra coat of mud than do any 'extra' sanding


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01-19-12, 10:41 AM   #11  
I am using a 6 inch knife. I have a 10" knife, but have never been able to get the hang of it and mud slings everywhere. Perhaps I could apply the mud with a 6" knife and then go back over it with the 10" knifie?

 
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01-19-12, 02:41 PM   #12  
That should work ok - you just want to make sure you use the the 10" knife before the mud has had a chance to think about setting.


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01-20-12, 08:28 PM   #13  
I pull the mud off the hawk with a 6" blade, then immediately switch to a 10". Get a lot smoother finish, and far less scraping and sanding required. And always a corner float for the inside corners.

 
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