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This may be an amateur question, but I am racking my brain to figure out what is happening. Appreciate any advice.

I am doing touchups to basic drywall with a flat latex, very light gray. I have the original paint that was used just a couple months ago, and so it has matched perfectly. One section I painted had some raised spackle though, so I sanded the paint itself and the spackle back down and painted it again. The paint matched perfectly again, but I hadn't painted as far to the edges as I should have, so a couple days later I went over it real quick with another coat.

This time, after matching perfectly twice, the same paint was a whole shade darker. It stood out like a sore thumb. The exact same paint, on the same spot, with the same roller, just two days after it had matched just fine. No dramatic temperature or humidity changes.

I've sanded the last paint coat off again, and the layer underneath is much closer to the right color, but now I don't know what to do. I've dabbed a few spots, and it seems like the paint is still drying too dark.

Is there some property of drywall that dictates that you can only ever paint it twice before paint starts drying darker? Or does one have to wait for longer than two days just to do another matching coat of a flat latex? This stuff dries in like 5 minutes so that doesn't seem right. I just can't figure out the physics of it, and I really want to be able to make it look right again.

I wish I had pictures of the whole process but I only have them as it exists now - I have sanded back down, you can still see the color and texture difference. It seems clear that just painting it again will still yield the darker color. I did a little test with primer too, but that didn't seem to change much. How can this suddenly change from matching perfectly to not matching at all?

Thanks!

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UPDATE: After sanding nearly to dry wall, I tried a dab just to the right of the hole, you can see it fairly clearly. I think it matches the surrounding paint pretty darn close. Thoughts?

UPDATE

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  • Sanding wall paint?? That's almost never necessary or advised. – isherwood Feb 2 at 22:05
  • Any suggestion? – number41 Feb 2 at 22:40
  • It appears that the patched sanded area is absorbing the paint differently causing a slight shade problem compounded by texture variance – Kris Feb 3 at 2:05
  • Yeah, it looks like a texture/absorption issue. Could also be didn't put enough coats on the first time so the white drywall/primer was printing through, and this is what enough coats looks like. – Harper - Reinstate Monica Feb 3 at 3:55
  • @Harper-ReinstateMonica I think not enough coats on the first time is the most likely cause - but since I got it to match the first time, could I sand a little more and paint again? Or do multiple coats change the drywall itself so much that it will never match again? – number41 Feb 3 at 4:25
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You probably didn't have the paint mixed well at one point and some of the color solids had settled out.

The best strategy now is probably to paint the entire wall after mixing thoroughly. Any variation will be masked by the natural light shift at the corners.

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  • Its definitely been mixed the same way each time, if solids had settled it would have been lighter, not darker, right? – number41 Feb 2 at 22:41
  • I wouldn't have any idea what pigments are in your paint. – isherwood Feb 2 at 22:54
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Paint is not quite opaque.

For instance if you painted a black and white checkerboard on a wall, and then painted over it 1 coat... the checkerboard would "print through" the paint. The paint areas over black would be beige but a tick darker than the actual paint... and the paint areas over white would be beige but a tick lighter than the actual paint.

We combat that problem partly by using primer, which assures the entire wall is the same color and texture before we begin.

We also paint the number of coats and WFT/DFT that the manufacturer specifies. At that point the paint should be its actual color and print-through should be reduce to nil.

Your problem is that the rest of your wall was under-painted, so it is a tick lighter than the actual paint. And you consider that to be "normal" even though it's not actually the color. When you patched that area, you accidentally put the correct number of coats on it, so you accidentally got the correct paint color. You think it's defective. It's the other way 'round.

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  • Thanks @Harper-ReinstateMonica, yes that's the theory I'm running with, but since I got it to match the first time, could I sand it down again and paint again? Or do you think multiple coats change the underlying substrate so much that it will never match again? I've already sanded down to where drywall is peeking through and re-touched, and I think it may match. Will try to get a picture. – number41 Feb 3 at 6:53
  • See update picture in post – number41 Feb 3 at 7:03
  • What is "WFT/DFT", for those of us not conversant in technical painting terms? – FreeMan Feb 3 at 12:18
  • Wet film thickness / dry film thickness. (harder to measure DFT so you often measure WFT). – Harper - Reinstate Monica Feb 3 at 17:22
  • @number41 You're not wrong that you're changing the substrate. First you're smoothing it and the rest of the wall is textured, and second, sanding down to substrate will change the paint absorption and cause a different finish. – Harper - Reinstate Monica Feb 3 at 17:25

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