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Old 02-01-2010, 07:53 PM   #1
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Bumpy ceiling: Skim coat?

Hi all, in the middle of my first DIY project involving drywall installation, a complete bathroom remodel. I started the entire room down to the studs including the ceiling.

For the drywall joints and screw holes I used tape and all-purpose joint compound. I did 2-3 coats for each joint and feathered out about 8-10 inches. I spent a good 6 hours sanding it into what 'felt' like a perfectly smooth surface. After applying 2 coats of Zinsser and a surface topcoat, I can see the bumpiness where the joint compound was applied.

I didn't notice it at first because I was using a shop light but when I turned that off and had just the ceiling lamp every imperfection is visible. There are bumps probably <1mm in height but even minuscule imperfections can be seen.

I read about 'skim coating' a light layer of joint compound but I didn't even get the joint compound PERFECTLY smooth where i applied it over the joints...even after sanding for what feels like forever.

How do you people get perfectly smooth drywall? Is there a 4 foot trowel you can use or something? Can I apply joint compound directly onto a painted ceiling/wall?

man...thought I was 99% done and now this...sigh.
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Old 02-01-2010, 09:52 PM   #2
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I think you did what most guys do when they first used spackle, you put it on too thick. You can correct it by skimcoating it with a THIN coat. Let it dry and get yourself a screen sander which covers a larger area at one time and prevents you from gouging the fresh spackle. You can try this and practice on a small section until you see better results. When you're satrisfied, then do the whole thing. You'll have to reprime before painting again. You can get away with a 6" knife for the skimcoat. A 12" works easier, but no sense investing in a 12" until you are better at it.


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Old 02-02-2010, 03:57 AM   #3
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After all that, use a flat paint, it will help hide all your mistakes, but you need a lot of work first.
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Old 02-02-2010, 06:18 AM   #4
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Originally Posted by chrisn View Post
After all that, use a flat paint, it will help hide all your mistakes, but you need a lot of work first.
Yup. And I disagree, the sooner you get comfortable working with a nice wide blade the faster you will be able to better blend in and skim coat properly. What better practice project than a bath ceiling people are at least not going to be seeing too often---one hopes?

Might want to invest in a variable speed orbital sander and boxes of bulk sanding discs to speed that part of things. Mine slows down to almost hand sanding speed so you don't have to worry about destroying tape and cranks up to some insane RPM. Basic sanders are the only tools I ever go lower end on. I find that drywall dust just eats away at motor windings anyhow. I paid $40-50 for this last one with 5" or something velcro sanding disc capacity. I use it all the time and have had it 5 years or so now but will not cry when it is time to dumpster it. Rube Goldberged tubing to the exhaust outlet so it goes into a shop vac with a drywall bag or filter.

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Old 02-02-2010, 06:44 AM   #5
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Agreed. You need a 12" taping knife. If you are using ready mix compound, stir it well before you start. Skim coat in one direction. Let dry. scuff off any ridges. Skim coat in the opposite direction. scuff off any ridges. I use a sanding block. You have to be real careful with a power sander or you can easily sand too much. When you get this far, take a light and shine it across the the ceiling. You'll be able to see any humps and valleys. When skim coating, do it in one continuous stroke. Don't start and stop. Don't overload your knife with mud. Go back and add as you need to, but always start at the beginning with your stroke. You should be almost out of mud when you get to the opposite end. Personally, I prefer a drywall trowel to a taping knife for skim coating, but that's a matter of comfort. Both will work. Don't get discouraged. Everybody on here started somewhere and their first jobs didn't look any better. Most just won't admit it. And, yes, you can mud over the paint.
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Old 02-02-2010, 07:55 AM   #6
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Originally Posted by Maintenance 6 View Post
And, yes, you can mud over the paint.
Personally, I would put a primer on though.
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Old 02-02-2010, 06:33 PM   #7
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I second the primer before skim coat.

The pic really makes this ceiling look bumpy.

It is a small ceiling area... it might be same time to take it down or rock over and mud. Your call,,, lots of high bumps might make this skim project very involved.

Lots of light is good for safety, but it can also blind you to the real condition of the surface you are working on. Check your work at the same light level it will be veiwed in. A hard lesson everyone must learn.

My lesson involved the underside of a warehouse roof.
I brought a 1000w Metal Halide flood light to light up the
painters work 35' up ( sissors lift and wand on the spray gun )

The paint job looked great until we turned the light off. LOL

PS. the trick to good mud work is less is more. Apply as little as you can.. 2 heavy coats does not = 3 thin coats.

Last edited by Big Bob; 02-02-2010 at 06:37 PM. Reason: add ps
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Old 02-02-2010, 10:15 PM   #8
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very common for new guys to put on too much mud. your wrists get tired fast and you just want to get it on. Just take your time.
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Old 02-04-2010, 10:11 AM   #9
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Are you using the compound straight out of the bucket?? It needs to be thinned to do a proper skim. A couple of thin coats is preferable to one heavy coat...
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Old 02-05-2010, 09:22 AM   #10
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You could add a texture to the ceiling to help hide the bumps, and use flat paint. I doubt you are going to keep that tree lamp in the bathroom. Turn it off and see how the ceiling looks.


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