Drywall skim.

Recently I installed 50+ 8'x4'x1/2" drywall boards in my basement. I wanted to do ALL the work on my basement finishing project. I taped, mudded and sanded all the joints and then primed everything with Gripper (Glidden, excellent product). After top coating the results were excellent.
Question. The pros put a 1/16" skim of mud over all the board surfaces. Why is this done? I did not do this because as a total amateur I do not have the skills. I have done everything else (electrics, plumbing, studs, drop ceilings, lighting, heating and ventilation, 25' wall of bookcases, media center with built in fireplace, etc) but skimming is way beyond my skills and you can't read books to figure out how to do it.
Why is a skim put onto drywall?
Peter.
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They do on lath board, but I don't ever see them do it on drywall. A good primer.. then paint or wall paper.
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PVR wrote:

From "Fine Homebuilding"
http://www.taunton.com/finehomebuilding/pages/h00132.asp
"Compared to standard drywall and joint compound, skim-coat plaster has greater impact and abrasion resistance, improved sound isolation, and can be brought to a truer flat plane resulting in a virtually flawless surface."
--
Jack Novak
Buffalo, NY - USA
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It isn't. Just mud the taped joints and the screw heads. Make sure they're smooth (probably two or three coats with sanding between each coat) and you're ready to prime.
-Don
--
"Ladies and gentlemen take my advice.
Pull down your pants and slide on the ice."
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It's a local thing. Isn't done in California, because the ground moves all the time, and we're forever repairing drywall cracks.
Here, there's typically a knockdown texture coating on drywall. Easier to repair in, when you need to in a couple three years.
And here, usually no basements, either. Water table is pretty variable, and there's not appreciable frost to account for, either, in many places.
Adaptable folks, humans.
Patriarch
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:
:> Why is a skim put onto drywall? :> :> Peter. :>
: It's a local thing. Isn't done in California, because the ground moves all : the time, and we're forever repairing drywall cracks.
Done here is Arizona, although we don't have earthquakes. Drywall hangers will spec either a smooth skimcoat or a textured one. The former is substantially more expensive than the latter. And to me at least, textured is nicer looking (if it's a fine, not really heavy, texture).
It's not necessary, but I find the look of plain painted drywall, with no texture, to be kinda cheap looking.
    -- Andy Barss
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They skim coat plaster on blue board, which has a paper face intended for skim coat plaster, but they generally don't skim coat drywall (Sheetrock) per se. If you used drywall, taping the joints and hitting the screws is the intended process.
John
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John Grossbohlin wrote:

A skim coat is usually 1/16" thick joint compound applied over "drywall" (Level 5 Finish).
"Veneered plaster" is a 1/8" of plaster applied over "blueboard".
From National Gypsum's web site:
http://www.nationalgypsum.com/resources/techtalk/revisiting.html
"Level 5 finish is recommended for areas where severe lighting conditions exist and areas that are to receive gloss, semi-gloss, enamel or non-textured flat paints. Level 5 requires all the operations in Level 4. Additionally, a thin skim coat of joint compound, or material manufactured especially for this purpose, is applied to the entire surface. (This definition is referenced to Terminology, Section II, Page 2 of GA-214 to make the description of "skim coat" clear to all.) The surface is smooth and free from tool marks and ridges. Before final decoration it's recommended that the prepared surface be coated with a primer prior to the application of final finishes. The Level 5 finish is required to achieve the highest degree of quality by providing a uniform surface and minimizing the possibility of joint photographing and/or fasteners "burning through" the final decoration."
--
Jack Novak
Buffalo, NY - USA
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wrote in message

I don't disagree... however in the context of his rock hanging in his basement with lots of bookshelves etc., tape the joints and hit the screws was the right process. Little if any direct sunlight happening in most basements... If he'd been talking about his living room that would be a different story!
John
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John Grossbohlin wrote:

Agreed, but PVR asked "Why is a skim put onto drywall?". He should know now.
--
Jack Novak
Buffalo, NY - USA
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PVR wrote:

Are you sure you're not talking about a veneer plaster (aka skim-coat plaster)? It is troweled onto blueboard, which is similar to normal wallboard panels.
Skimcoating _is_ also done with drywall in places where you need a higher quality finish. The drywall paper and the mud have different surface properties (texture and absorption) which can be visible in the finished wall in some circumstances, most notably with extreme lighting and/or higher gloss paints. This is known as telegraphing or banding. A skim coat helps even out the surface differences. It also protects the paper from fuzzing during sanding, which is a common problem for DIYers.
The skim coat is just thick enough to cover, not a full 1/16", so it is probably not beyond your abilities if you were able to mud the basement yourself. For future reference, they do sell a pre-skimmed wallboard.
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I thin the mud and roll it on with a paint roller. Then I scrape it off with a wide knife. The mud left behind is very thin, too thin to measure thickness. This thin coat makes the wall surface uniform and ready for paint. I only do this when I want a smooth surface with no texture. If this is not done the sheetrock has a different surface than the seams and this can show thru the paint.
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I prime, sand the primer with a fine drywall screen equipped pole sander, and then reprime to deal with the variance between the joint compound and the drywall paper. I heard about this from a guy who did high end finish work in NYC. He suggested it as a way to deal with a really crappy rock and tape job that I inherited where the guys had scuffed the paper all over the place when they sanded it... It worked so good on that repair job that it became my standard process when the job had to look good. I found that the primer rolls on quick and dries quick compared to a joint compound skim job.
John
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Some pros did mine and they SPRAYED the finish on. The particular product was to have an elasiticity better than some others available (FWIW Rucoat Equalizer). That was to avoid hairline cracking.
Afterwards, I took a drywall sander to level and then applied my paint directly. NOVA notes that primer should be used and his reply has more info than I knew - thanks NOVA.
Whether your lighting requires it or not is up to you. Let me say this much, it's a beautiful finish. I've got expansive walls, ceilings, skylights, large windows, and a tray - you don't see a thing but surface! The cost was something like $500 extra (might have been less) for the whole house - an advantage of being your own contractor probably. Sorta like going from R30 to R38, and insulating the whole garage, and insulating every wall in the house, was only a few hundred dollars extra when I negotiated directly with the sub.
BTW I'm still finishing the downstairs so I'll be where you are soon again. The way I laid out my shop electrical would have cost me a fortune if an electrical contractor had done it.
TomNie
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Peter, There was a time that I was a pro. I (we) never skim coated rock. You may be thinking of plaster. We (I) would 'skim coat' blue board, but we applied at least two coats and the finished thickness was probably an eighth inch or a bit more. Hank
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Don't know. Hung quite a few sheets in my time and never thought to do a skim coat (don't think I could, know I do not have the patience!).
But, for shops, I would install plywood above the bench height for a secure nailing/screwing surface and use drywall for the ceiling and get a cheap spatter/texture gun from Harbor Freight ($17) and texture the heck out of it. before primer and paint. I finished mine with a high-gloss Latex enamel that reflects lots of light.
BTW - a recent sale at Lowes called my attention to the (apparent) fact that OSB can be had for about half the price of Sheet rock! Bitch if you're doing a living room, but a God send if you're walling in a shop!

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Never seen new drywall skimmed, myself, but I've done it more than a few times to repair pitted walls or cover orange peel or sand texture. Sometimes, it's the only way to get a decent surface short of gutting everything and starting over.
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