Two questions on new drywall and old drywall

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Old 12-30-10, 08:33 AM
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Two questions on new drywall and old drywall

What is the best primer to use on new drywall?

Also, I have some left over drywall that had paneling on it previsouly.
When The paneling was removed (it was applied with liquid nails) a lot of the paper came off as well. Is there a way to salvage this drywall?

Many thanks in advance and Happy New Years to all......
 
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Old 12-30-10, 09:05 AM
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Drywall's pretty cheap, I wouldn't screw around with damaged sheets

I prefer Zinnser primers, 123 is the one I use for new drywall
 
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Old 12-30-10, 10:00 AM
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"The paneling was removed (it was applied with liquid nails) a lot of the paper came off as well. Is there a way to salvage this drywall?"

Yes, if you apply a coat of oil base primer or zinnser's gardz to the raw gypsum, once dry you can apply a thin skim coat, sand, prime and paint.

Zinnser's 123 would be a good primer for new drywall although most any latex wall primer will do ok.
 
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Old 12-30-10, 08:15 PM
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Crater22:

You need to know that the surface paper is important to the strength of the drywall.

You see, paper is very strong in tension. Try pulling hard enough on a $1000 bill to tear it into tow pieces and you'll see what I mean. For drywall to bend, then the paper on one side or the other of the drywall has to stretch to accomodate the new shape. Since paper is very strong in tension, then the paper on both sides of the drywall is going to resist stretching with considerable force. THIS is what makes drywall rigid considering the filmsy materials from which it's made. But, it also means that the integrity of the paper on both sides of the drywall is crucially important to maintain the strength of the drywall.

If you have exposed gypsum on your old drywall, you can still repair the drywall if you'd prefer not to replace it. Simply apply fiberglass mesh drywall joint tape over the areas where the paper is missing, or largely gone, and then paint over that fiberglass mesh tape with white wood glue diluted with water to make it into a paintable consistancy. As the glue dries, it'll bond the fiberglass mesh to the gypsum core, thereby providing the same (if not better) resistance to bending that the missing paper did.

If you do this, apply two layers of fiberglass mesh; one horizontally and one vertically, painting with dilute white wood glue after each layer of fiberglass mesh. And, run the fiberglass mesh over the surrounding paper for several inches in order to ensure good adhesion between the fiberglass mesh and the drywall's surface paper.

After doing the repair, skim coat the fiberglass mesh with joint compound. There are two newbie-friendly ways to do that; one is to use a "V" notch adhesive trowel to spread joint compound over the repaired areas, allow the joint compound to dry, and then, holding that adhesive trowel upside down, fill in the trowel ridges with more joint compound using the straight (ie: unnotched) side of the trowel. Allow to dry, sand smooth, touch up as necessary, prime and paint. The second way is to use a "V" notch adhesive trowel to spread a uniform amount of joint compound over the area of the repair, then mist the fresh joint compound with water from a spray bottle, and then trowel that joint compound down flat and smooth.

Then allow your skim coated joint compound to dry, sand smooth, prime and paint.

PS: Reinforced concrete works on exactly the same principle as drywall. Steel is very strong in tension. Concrete is weak in tension; it's not that hard to pull on a concrete block to break it. So, if you embed steel rebar near the top and bottom of a concrete slab, then the steel rebar near the top or the bottom has to stretch in order for that slab of concrete to bend, and the slab has to bend sufficiently far before the concrete in it breaks. So, when you see a large concrete slab, like those used for the roadways on bridges, you can be confident that it's the rebar inside those concrete slabs that's resisting 99.9% of the bending forces, not the concrete itself. Were it not for the rebar inside that concrete slab, the slab would bend until it broke, and that's game over for that bridge. When you think of drywall, think of the paper as acting exactly the same as the rebar in concrete, and the gypsum core being the concrete itself. (Real concrete slabs have the rebar just a few inches under the surface on both the top and bottom of the slab, but the working principle is the same.)
 
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Old 12-31-10, 04:01 AM
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While Nestor's method would make for a stronger wall - that's a lot of work and imo unnecessary. Drywall isn't structural - just a covering for the framework behind it.
 
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Old 01-01-11, 11:12 AM
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Well, it's up to each individual to decide what to do in each case.

I'm just providing people with a reasonable alternative that falls between simply painting over the damaged surface paper with Guardz and replacing the drywall. Many newbies might not realize that it's possible to repair severely damaged drywall.
 

Last edited by Nestor; 01-01-11 at 11:50 AM.
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Old 01-01-11, 01:07 PM
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I don't think anyone has said to just paint over the exposed gypsum with gardz. The Gardz or an oil base primer should be applied to the exposed gypsum so there won't be any issues with skimming over it with j/c. I've repaired countless walls where the paper had been torn off of the drywall. I usually used whatever interior oil base primer I had on the truck, skimmed with j/c, reprimed and painted with latex. Never had any issues from repairing the wall that way.

IMO adding the fiberglass mesh is a lot of extra work with very little benefit. While it is beneficial to use the mesh over damaged portions of the drywall, it simply isn't needed where the only damage is the missing paper.
 
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Old 01-04-11, 06:03 AM
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Two answers for new and old drywall

(I just had to put that title on this post)

1. The best primer for new drywall is the time tested PVA drywall primer. These have been used for years on new drywall. A good one it Sherwin Williams Promar 200 or Promar 400 primer. I think the PVA primers do the best job of wetting the surface and give the best adhesion. Remove sanding dust by vacuuming, wiping with a micro fiber tack cloth, or using a "mop" duster like Wooster's Dust Eater before priming.

2. When you have torn paper facing on drywall you have the potential for blistering if you don't get all the delaminated paper glued back down. The delamination of the paper facing is usually not all the way through the paper facing. There are a few specialty primers out there designed for this very situation, one of these is Zinsser's Gardz. Follow the label directions and it will prevent blistering problems. Gardz is not just a typical primer, it is more like a "glue" that will penetrate through the paper (at least to a certain degree) and bind the "layers" together. It is important to put in on "liberally" to fully saturate the paper in order to get good penetration.
 

Last edited by Slatz; 01-04-11 at 06:58 AM.
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Old 01-11-11, 10:56 AM
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I removed tile from my backsplash and this is what happened. How should I repair this? I will re-apply the tile after repair of the wall. Some of the gouges are very deep down to the other side of the paper. If I'm understanding what I've read thus far, in this case I should apply Gardz directly to the exposed gypsum to help prevent crumbling so that joint compound can be applied effectively. Someone suggested in another forum to just skim with thinset before applying the tile. Should I use mesh tape to replace the paper thats partially responsible for since the wall is partially supporting the cabinet above?



Thanks for any help
 

Last edited by t2star; 01-11-11 at 11:40 AM.
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Old 01-13-11, 01:19 AM
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T2star:

If that wuz my house, I'd dilute some white wood glue with water and paint over the exposed gysum patches with that dilute glue, and allow time to dry.

Then, I'd fill in the areas where gypsum is missing using a wide (14 inch) trowel, or a standard size (11 inch) trowel using joint compound.

Then, I'd apply fiberglass mesh in two coats in both directions over the entire area you've removed the tile from, painting over each coat with dilute glue to bond each layer of fiberglass mesh to the gypsum core of the drywall.

Then, I'd skim coat over the fiberglas mesh tape with joint compound.

Then, I'd scrape/sand the joint compound smooth. Use paint scraper for early coats, and hand sander to final coats.

And then I'd prime and paint.
 
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Old 01-13-11, 06:32 AM
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We've had this basic question a lot over the years, Nestor recommends a process most of the rest of us think is overkill

I would seal the exposed gypsum with Zinnser Gardz, fill with joint compound and then prime the whole surface before putting tile back on
 
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Old 01-13-11, 09:13 AM
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Mitch, your way was what I originally planned to do but I decided to patch it with thinset since I was told would be equally as effective. The recesses in the gouges were deep enough that I was unable to fill them completely the first time so I will need to go over it again. Twenty two hours later there are still areas not completely dry. Is it ok to go over it again before its cured? How do I level out the wall to accept tile? Low grit sandpaper? Joint compound would have been easier to sand.

Nestor, your method may be overkill but I'll bet you do excellent work!

Barry
 
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Old 01-13-11, 11:04 PM
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T2Star:

Yep, the thicker the patch of thin set you apply, the longer it's gonna take to dry. Seeing the thin set still damp after 24 hours doesn't surprise me if the patch is 1/4 inch thick or so.

Obviously you can't sand the damp patch down cuz it'll only gum up your sandpaper, but you should be able to scrape it down with a paint scraper. That's always recommended cuz it's vastly easier to add more thin set (or joint compound) than it is to remove thin set (or joint compound) and that's especially true if you're using a polymer modified thin set that will dry too hard to sand.

The advice you received was correct. If you're planning on tiling over that damaged drywall, then filling the gouges in the gypsum with thin set would work as well as using joint compound. Thin set doesn't spread with a trowel quite as well or as smoothly as joint compound does, but that won't be an issue if you're gonna be tiling over the thin set anyhow.

But, don't use a polymer modified thin set. It will dry WAY too hard to sand smooth.

As long as you don't use a polymer modified thin set, then the thin set should dry soft enough to be sanded smooth very easily with 60 grit sandpaper. I've sanded Mapei Keribond Grey down using 60 grit sand paper, and it practically falls off the wall. And, once sanded smooth, you can then dilute white wood glue in water and paint it over those thin set patches using a paint roller sleeve. The dilute glue will be absorbed into the thin set and will glue all the cement grains together as it dries, thereby hardening the thin set to the same strength and hardness it would be had you used polymer modified thin set in the first place, and then were somehow able to sand that hard polymer modified thin set smooth. (The "polymer" in "polymer modified thin set" is really just an powdered adhesive that makes the thin set stick better and dry to a tougher cement than it would without that glue inside it. It sands very easily without the glue in it, but dries too hard to sand smooth with the glue in it.) Keep on painting over the thin set with dilute white wood glue until you no longer see any "darkening" of the thin set as you apply more dilute glue. The darkening of porous materials when they're wet is due to the fact that water has a refractive index closer to that of solids than that of a gas like air. Consequently, light refracts through a smaller angle when it passes through a wet material than a dry material (like wet cotton and dry cotton). The result is that light travels a straightER path as it enters a wet materais, and consequently travels straight into the wet materials where it is absorbed. This is precisely why your blue jeans are darker when they're wet, and it also expains why a wet cotton T-shirt on a girl is more transparent than a dry cotton T-shirt on a girl. If light travels a straightER path through wet cotton, it's behaving more like it would if the cotton T-shirt weren't there, in which case it behaves more like it would if that wet cotton T-shirt were transparent.

Since it's the absorbtion of moisture into the thin set that causes it to darken, then once you see that painting dilute glue onto the thin set isn't causing any darkening of the thin set, then the thin set is no longer absorbing that glue, and painting glue on is only resulting in a film of glue forming over the surface of the thin set. That's your que to stop applying glue to the thin set.

If you intend to use polymer modified thin set for your tiling, and don't want to buy a nonpolymer modified thin set like Mapei Keribond Grey, then I'd say you should use an "All Purpose" joint compound to fill the gouges in the gypsum. At least then you'd be able to sand that All Purpose joint compound down without a major fight.

If it were me, I would go to any sheet metal shop and get a 3 foot long by 4 inch wide piece of 10 guage (or even heavier) sheet metal bent into an "L" shape profile; 3 inches on the long arm and 1 inch on the short arm, and use that as your trowel to spread the thin set over the wide gouges in your drywall. I'd paint the exposed gypsum on that wall with dilute white wood glue first so that the thin set sticks better to it. As long as you use a wood glue, then even if the glue dries on the bare gypsum, the moisture of the wet thin set will re-activate the glue ensuring the thin set sticks well to the gypsum.

Even though I post in the Painting forum, I've done more than my fair share of ceramic wall tiling. I'm concerned that if you don't get your wall reasonably flat, the large tile size you're using is going to make for potential problems setting that tile. Any "unflatness" in the wall may result in the tiles not meeting properly because they'll each be in a slightly different plane. The larger the size of the tile you use, the less well the tiles will conform to the contour of the wall, and the greater the potential problems setting the tiles.

To overcome that problem, I'd buy a roll of 1 inch wide double sided tape (from any of the places listed under Tape or under "Adhesives" in your yellow pages phone directory). Use that double sided tape to stick 60 grit sandpaper to the wider 3 inch arm of the piece of sheet metal you used to spread the thin set with. Use that tool to sand down those areas of your thinset that are almost 3 feet wide. As long as the sandpaper covers the middle portion of the sheet metal with some bare sheet metal at both ends of the tool, it'll stop sanding when the thin set is flush with the surrounding wall. Sand down the widest patches first, and remove sandpaper from the edge of the spirit level as the width of the thin set you need to sand down becomes narrower. You should be able to remove the old sand paper from the tool with a cheap wood chisel and some mineral spirits, and apply new double sided tape and sand paper as may be required.

Also, use that same double sided tape to stick carbon paper to the 1 inch wide arm of your tool. By rubbing the carbon paper against the wall, you'll mark the high spots that need to be sanded down to make the wall flatter.

Spend a few evenings sanding the patches down flat with your tool, and checking with the carbon paper, and your wall should be flat enough to tile with the gigantic tiles I'm seeing in the pictures.

Or, seeing what I'm seeing in the pics you provided, that's probably the game plan I'd opt for to prep the wall for tiling. Others in here may have different (and possibly better) ideas.

But, I wouldn't invest all that time and work tiling the wall before I either replaced that drywall or restored it back to it's original strength using fiberglass mesh drywall joint tape.
 

Last edited by Nestor; 01-14-11 at 12:03 AM.
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Old 01-15-11, 01:28 AM
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I agree with mitch17, Gardz, skim then prime. You could just use Gardz again over the top after sanding smooth and removing sanding dust, but I would probably use an oil primer.

There is no sense in a long, over done repair method here. If a section drywall is badly damaged, (it doesn't appear to be that way from the photo), then cut it out and screw in a new piece. Then tape the seams. That can be done in a matter of minutes.
 
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