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Old 07-05-2008, 12:15 PM   #16
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Re-Painting textured walls: the Frustration


Now that I look more closely at the walls, the problem seems to be that some areas were overworked with a roller. Also there are some places where he touched up while the paint was still wet, so those spots are a different shade than the rest of the wall. I don't see any drips or raised areas of paint. I'm starting to think that sanding it would just remove the paint altogether. What's the purpose of sanding the walls between coats? And by "scuffing" do you mean just one light pass with a pole sander?

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Old 07-05-2008, 04:35 PM   #17
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Re-Painting textured walls: the Frustration


Sanding between coats removes lumpies, klingons, roller fuzz, bugs, etc., and helps give the next coat some "tooth" (adhesion)

A scuff sanding means a very light sanding

My preferred method would be a sanding screen on a pole sander
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Old 07-05-2008, 11:15 PM   #18
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Re-Painting textured walls: the Frustration


Will painting the 2nd coat without sanding the 1st coat cause any problems with the finish? Would the overworked and touched up areas in the 1st coat show through to the 2nd coat if I didn't sand the walls? My husband thinks that sanding these textured walls is a bad idea.

I'm just trying to get this project finished. Since we are working on the painting in shifts due to his work schedule and our baby's schedule, it's taking a lot longer than it should. I'm worried that our paint is going to get thick and hard to work with since it's sitting in a 5 gallon bucket that is only a 1/4 filled.
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Old 07-05-2008, 11:39 PM   #19
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Re-Painting textured walls: the Frustration


New2DIY:

Do you mind if I ask what kind of paint your first coat was. That is, colour, chemistry (oil or latex) and gloss level please?

I'm wondering if their discontent with the paint job may just be incomplete hide after one coat.
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Old 07-06-2008, 12:25 AM   #20
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Re-Painting textured walls: the Frustration


I'm using Pittsburgh Paints Pure Performance Latex in Eggshell the color is Antique Moss. The problem is not the paint. My husband was using poor technique on the walls that he did and ended up with over worked areas and roller marks. The walls that I did using proper technique look great, and only need a second coat to cover the "holidays" that inevitably show up when painting textured walls.
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Old 07-06-2008, 03:10 PM   #21
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Re-Painting textured walls: the Frustration


Well, everyone in here gives the best advice they can based on their own personal personal knowledge and experience. These vary between people, so you may get different advice from different people.

My understanding is that you're being told to sand down the paint that your husband put on in order to improve adhesion of the next coat to the coat your husband put on.

Since these are textured walls, I really have trouble imagining how a person could do any more than sanding down the peaks of the texture that are sticking out proud of the wall. In order to sand that paint for good adhesion, it would presumably be necessary to sand between those peaks as well. However, I personally don't believe any sanding is necessary.

I don't believe you need to sand those walls because you're painting over a flat "Santa Fe" latex paint with an eggshell latex paint. BOTH the old paint and the new paint are already rough enough to ensure good adhesion of the next coat. (Technically, the reason why sanding improves the adhesion of latex paints is because it increases the surface area over which that adhesion occurs.) THIS is why they recommend sanding down semi-gloss and gloss latex paints before repainting; to increase the surface area between the two films. If you are painting over a flat latex paint with an eggshell latex paint, both already have boatloads of surface area. Sanding will not increase the surface area, it'll only damage your wall.

You don't really need to know this part:
A micron is one millionth of a meter, or a thousandth of a millimeter. A human hair is typically about 100 microns in diameter. The limit of human vision is about 20 microns; anything smaller than that we simply can't see. The "extender pigments" they add to primers and flat paints to make them dry to a flat or eggshell gloss are about 10 microns in diameter. A red blood cell is about 5 microns in diameter. And, finally, a single latex paint resin is about 1/10th of a micron in diameter. So, even if you were to sand that paint down with the finest sandpaper you can find, that surface would still appear to be like huge sand dunes to a latex resin. There still wouldn't be anything small enough for latex resins to solidify around and thereby "grab onto". Thus, it's the increase in surface area that promotes better adhesion, not that sanding creates "keyways" in the surface that latex resins can "hold onto". And, alkyd resins are vastly smaller still than latex resins. Alkyd resins are better discribed as very large molecules.

(and truth be told, you don't really need to know this next paragraph, either)
Also, furniture makers will sand their finish down periodically between coats. And, as stated previously, the purpose in doing this is to remove any imperfections in the surface which would affect the smoothness of subsequent coats of varnish, shellac, lacquer, polyurethane or whatever. But, they won't sand after every coat. They'll sand after every 2nd or 3rd or even 4th coat to remove imperfections. During the coats in between sandings they simply try to put each coat on within 24 hours of the previous coat in order to ensure good chemical bonding between coats for maximum adhesion. That is, after every 2nd, 3rd or 4th coat of finish, they'll allow the finish to fully cure (or dry) and then sand down to remove any imperfecions, and the roughened surface will ensure good adhesion when they apply a subsequent coat. Between those sandings, they rely strictly on chemical crosslinking between coats to ensure excellent adhesion. And, they do this in order to achieve a mirror smooth finish. You, on the other hand are applying an eggshell gloss paint. It ain't gonna be no mirror smooth no matter what. It's going to dry to a relatively low gloss even if you sand until your fingers bleed.

Here, do this:

Hold a bright light up to the wall your husband painted and see if you can see a distinct "ridge" where the roller marks are. If so, I would simply take some acetone, lacquer thinner or xylene on a paper towel and clean those ridges off. (Acetone smells the least of these chemicals, but evaporates the fastest giving you the shortest working time between wettings. Lacquer thinner gives you a longer working time, but smells the most. Xylene gives you the longest working time, but is the least agressive when dissolving latex paints. All three will evaporate completely without leaving any residue. You can use Goo Gone to remove latex paint, but it will leave behind an oily residue which you will then have to remove with some other hydrocarbon, probably paint thinner. PS: all those solvents will damage acrylic products, including acrylic floor "wax". None of them will harm the fiber of a carpet, but paint-laden drops of solvent could leave paint in your carpet that may be hard to remove, so it's a good idea to spread out a drop cloth out before you clean those roller marks off.)

Getting back off the tangent to the subject at hand...

So, if you see ridges where your husband rolled, then you can simply clean off those roller ridges with a strong solvent so that they don't show through your next coat.

If you don't see any ridges with the bright light exagerating their height, then you're only seeing an increase in colour density along those lines because of the thicker coat of paint. In that case, I would simply proceed to put on another coat of your "Antique Moss" eggshell latex paint.

And, if push comes to shove, and you see any such ridge lines showing through that second coat of paint, you can do the same solvent trick to remove them, allow to dry, and then paint over only those areas where you messed up the paint with the solvent.

Everyone will give different advice in these forums based on their own personal knowledge and experience, but I would highly recommend that you contact someone who's knowledge you trust and ask them if it is necessary to sand an eggshell paint before applying another coat. In my view, if you see something sticking out of your last coat of paint, remove it with your fingernail or a paint scraper and continue painting. I simply don't believe sanding down a textured wall is either feasible or beneficial to achieving a good paint job here.

But, I don't want to make enemies here, so if someone disagrees, I'm more than happy to discuss the technical merits of sanding this painted wall down as long as we can keep the conversation on a technical level and not let it degrade into an insult hurling contest. I am a poor insult hurler.


Last edited by Nestor_Kelebay; 07-06-2008 at 03:30 PM.
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