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Old 12-22-2008, 12:05 AM   #16
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Painting Question


J. Weiner:

The blue pigment used in the paint tinting machine to tint paints blue is "phthalocyanine blue", and it has mediocre hide. It, and it's very close cousin, "phthalocyanine green" were both discovered near the beginning of the 1900's, and the green pigment is made by chlorinating the blue pigment. Both have mediocre hide.

The "streaking" that's visible on your ceiling is due to the fact that two coats of your blue paint hides better than one coat. And, most likely three coats will hide better than two. How many coats you have to put on to achieve full colour saturation is a guess right now.

That is, the multiple coats of paint needed on your walls is both partly due to the fact that you didn't use a tinted primer (so more of your paint is being absorbed into the porous drywall and joint compound rather than remaining on the surface to help hide the underlying white colour, and partly because of the poor hide of the paint colour you chose.

Drywall and joint compound are porous materials. Primers have huge rocks in them that are almost large enough to see with the naked eye called "extender pigments". The job of those extender pigments is to plug up the porous surface of drywall paper and joint compound so that more of the subsequent top coat of paint remains on the surface rather than being wicked into those porous materials. You CAN use a paint as it's own primer, but it's an expensive option. A cheap primer can both be tinted to give you a head start on changing the wall colour, and it will minimize any paint absorbtion into the drywall paper and joint compound.

Now that you've painted these walls, your best bet is to keep painting them blue until you achieve complete hide of the underlying drywall and joint compound. When you do that, you won't see any difference in the colour saturation by adding an additional coat. Right now, the difference between one coat and two is blindingly obvious cuz of the blotchiness on your ceiling and the streaks on your walls where two coats overlapped.

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Old 12-22-2008, 10:35 AM   #17
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Thanks for the great info!! So, I guess the bottom line take home message is to always use a primer first on bare drywall.
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Old 12-22-2008, 10:38 AM   #18
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Your welcome.

Yes always prime bare drywall with a quality primer designed for that purpose. You'll get a better looking longer lasting paint job with less effort [and paint]

Good luck!
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Old 12-22-2008, 02:52 PM   #19
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Quote:
Originally Posted by Sammy View Post
Fire the paint guy.

Possible he didnt understand you had bare walls versus walls that were already painted and just doing a color change.

Some of the streaks are your drywall joints showing thru since the joints and the drywall with no compund will absorb paint at different rates. Other streaks may be from application.

If you do five more coats it might even out the way you are doing it now.

I would leave it dry, then prime it with a tinted primer. This will help even out the absoprtion rate... Then top coat.

Make sure to tint the top coat paint by mixing some of each can together in a bucket so the whole batch is the same color. Important on large walls and darker colors.

Take the pics with you when you go back to the paint store.

Rollers can be used for 6-8 hours if they arent left unwrapped during breaks but at the end of the day its clean it or toss it in my book.
Yep, it kinda looks like you have paint still soaking into the joint compound even after 2 coats. Paint "can" self prime, but it won't really seal as well so even more coats may be required. It won't bond as well so you could have pealing. It won't be as durable so you could disturb the paint with normal traffic against a wall or if you try and scrub it.
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Old 12-22-2008, 03:05 PM   #20
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Well . . . . I will definitely be using a (tinted) primer for the rest of the room in my basement. Thanks for all the good info.
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Old 12-22-2008, 04:45 PM   #21
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I'm not a painter by trade either, but I wouldn't even think of painting raw drywall without primer. It equalizes the "suction" between the drywall paper and the joint compound. They absorb paint at different rates and your joints and nail/screw spots will "flash" if not primed. Looks to me like you may be experiencing that at least to some extent (pic #1). Also looks like you're trying to go too far with the paint on the roller (pic #2). Get a clean 5 gal. bucket and a roller screen, pour your paint in the bucket and roll out of it, not a tray. Keep the roller full. One other thing, is this "eggshell" paint?? If so, it will never look right without primer! If the walls weren't finished to a level 5 finish (basically glaze coated with mud prior to sanding) the joints will show for sure.
I'd go back to the S/W store and ask to speak to the mgr. Ask HIM if he'd recommend not priming raw drywall. If HE says it's ok, I'd find another paint store.......
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Old 12-22-2008, 08:26 PM   #22
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I wouldn't even think of painting raw drywall without primer. It equalizes the "suction" between the drywall paper and the joint compound. They absorb paint at different rates and your joints and nail/screw spots will "flash" if not primed.
You're right that if you paint over unprimed drywall, you will see the joint compound as "flat" areas on an otherwise glossier paint. That's because the joint compound is more porous than the drywall paper, and it takes bigger plugs to plug up the joint compound. I think you're right in calling that effect "flashing", which in paint terminology means non-uniform gloss.

It's not that the primer "equalizes" the ability of the drywall and joint compound to wick primer in, it's the fact that the primer contains huge rocks that are almost large enough to see with the naked eye, called "extender pigments". As the primer gets wicked into both the drywall paper and joint compound, these huge rocks get carried along and plug up the porous surface of the paper and joint compound so as to prevent any further absorbtion of the primer. So, more of the primer remains and dries on the surface rather than inside the substrate. If you were to use paint instead of primer, you wouldn't have as many big rocks to plug up the big holes, and more paint would be absorbed by the joint compound rather than the paper, leading to the "flashing".

Extender pigments come in different materials (like talc, chaulk and pulverized silica sand (quartz)) and in different grinds; from very fine to coarse. The flatter the paint, the more extender pigment in the can and the coarser that extender pigment will be. It's extender pigments that make paints dry to flatter sheens. If there were no extender pigments in paints, all paints would dry to a high gloss.

So, if J. Weiner were painting with a DEAD FLAT paint, he could probably get away without using a primer. The reason why is that flat paints have pretty coarse extender pigments in them too, that would do the same job as the extender pigments in primers.

I expect primers would use softer material (like talc and chaulk) in their extender pigments, wheras good quality paints would use a harder material (like ground silica sand), but I really don't know if flat paints use finer ground extender pigments than primers. I have had professional painters tell me that they use flat paints as their own primer, so from that one would presume that the extender pigments in flat paint work just like those in primers. Aslo, if a flat paint dries to about the same flatness of finish as a primer, then you'd expect there would be similarity in the amount and size of extender pigments in the two cans.

So, I think that quote should read:
"I wouldn't even think of painting raw drywall without primer, unless I was applying a flat paint."
Cuz then, the paint would make a much better primer.

PS: Also, primers will often call themselves a "Primer/Sealer". The purpose of a "primer" is to stick well to the substrate and provide a surface which the subsequent paint will stick better to. The purpose of a "sealer" is to prevent fluid penetration into, or out of, the substrate. In the case of a primer, it's the extender pigments that do both jobs. They cause the primer to dry to a matte finish that paint will stick well to, and they also plug up the porosity of the substrate to seal the surface.
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Last edited by Nestor_Kelebay; 12-23-2008 at 12:49 AM.
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Old 12-23-2008, 06:59 AM   #23
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So I guess the only good news in all of this is that the blue paint I am using is actually a "flat" paint! :-)
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Old 12-23-2008, 10:59 PM   #24
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[QUOTE]So I guess the only good news in all of this is that the blue paint I am using is actually a "flat" paint! :-) [/QUOTE]

That's probably why SW said you didn't need a primer.

The reason why it's taking several coats to put the paint on is because of the mediocre hide of the blue pigment. It simply doesn't hide in one coat, and it might not achieve complete hide in two coats either. You may be looking at three coats to get complete hide. It would be even worse had you opted for a high gloss blue paint.

The differences in colour intensity in the pictures you posted are the direct result. The areas of darker blue are places where two coats of paint overlapped. When you paint over this, keep an eye out for that same variation in colour intensity. But, this time the difference in intensity will be three coats hiding better than two. Once you can't see any variation in colour intensity on the wall, then you know you've hidden the substrate completely.

So, the reason why it's taking several coats to paint each wall isn't so much the lack of a primer but the fact that the pigment in your paint doesn't provide good hide, so you end up having to use multiple coats of paint on each wall.

Also, some company's "flat" paints are flatter than those of other companies. If you can see a difference in GLOSS from the drywall paper areas to the joint compound areas, there may still be some differential paint absorbtion going on. The second picture you posted kinda suggests that, but I think that's just differing colour intensity where coats overlapped; a sure sign of insufficient hide.

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