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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!

enter image description here

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, 2021 at 22:05
  • Any suggestion?
    – number41
    Feb 2, 2021 at 22:40
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    It appears that the patched sanded area is absorbing the paint differently causing a slight shade problem compounded by texture variance
    – Kris
    Feb 3, 2021 at 2:05
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    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. Feb 3, 2021 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, 2021 at 4:25

3 Answers 3

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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, 2021 at 6:53
  • See update picture in post
    – number41
    Feb 3, 2021 at 7:03
  • What is "WFT/DFT", for those of us not conversant in technical painting terms?
    – FreeMan
    Feb 3, 2021 at 12:18
  • Wet film thickness / dry film thickness. (harder to measure DFT so you often measure WFT). Feb 3, 2021 at 17:22
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    @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. Feb 3, 2021 at 17:25
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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, 2021 at 22:41
  • I wouldn't have any idea what pigments are in your paint.
    – isherwood
    Feb 2, 2021 at 22:54
  • It depends which pigments settle first and how they they mix back in, could be lighter or darker or a different hue if not fully mixed.
    – Jasen
    Oct 2, 2023 at 23:56
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A few suggestions:

In general, shouldn’t matter what color was on the wall, the paint will cover. Going from dark to light is possible, but it generally takes more coats. I’d recommend you apply a primer first if going, say, from black to white —- just for the savings.

This might be slightly counter intuitive, but the above also means that if you’ve applied a number of coats until you’ve reached the color in the can, then adding one more coat on top will not make it darker than the color in the can. @Harper’s theory makes sense in that regard — it could be that the patch has reached the final color, and it’s the rest that requires additional coats.

other possibilities:

The chemicals and pigments can separate over time (even in the course of days), so you’re encouraged to stir the paint before you reuse. Re-shaking is fine too, except if it’a a very old can with a bunch of crusty rusty bits on the underside of the lid.

In that vein, if the paint was mixed at two different occasions it could be a slight variation in product or dosage (different staff, or different mixing machine calibration). Just last month, i went to Benjamin Moore to buy more of the same paint, and received a can with a different label. Their formula had changed slightly — the clerk recommended i throw away my rolls if they were covered in the paint from the previous can. That’s probably a rare event though.

Some stains on walls can percolate back onto the surface of the paint slowly. Examples are pen ink, water stains (usually on ceilings), and rust stains (from nails/screws). It won’t matter how many coats of paint you add, it will still scream at you eventually. Another possibility is that whatever’s on the surface (e.g. spackling) absorbs the paint differently, like a sponge, and the color and light shine differently. For these, you would apply a shellac based primer (like Kilz, or from Zinsser) before you roll on the paint.

If you believe there’s a contaminant in your paint, change your roll (or wash it really thoroughly)

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