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Old 02-04-2024, 00:22   #1
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Strange marks on Plywood after painting.

Hi,
just repainted some panels.
Upfront, I am for a good workboat finish not for glitzy yacht finish.

Prep was sanding, followed by thorough dedusting with vaccum cleaner and wipe with Acetone. The Acetone was allowed to flash off for an hour.

Substrate is previously painted plywood panels, fillered in some areas with polyester putty.

Paint was applied by roller.

The paint is a alkyd resin varnish, suitable for bathrooms and the like. The panels are in the interior but not exposed to water or chemicals like petrol, diesel or similar.

I have one panel where I now see these marks in the photo. All other are OK. They appeared already during painting and kept coming back every time I rolled over them.

What is the reason (resin in the wood veneer??)?

What are the remedies (sand the area, filler with polyester putty and repaint?)?

Thanks for suggestions.
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Old 02-04-2024, 00:36   #2
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Re: Strange marks on Plywood after painting.

Franziska that looks like small voids in the final plywood skin Nothing serious, but you could fill it with some of that polyester putty that cures in 5 minutes. When I used to paint plywood with epoxy undercoat, I would lay it on thick then spatula the paint into all the voids. Even then when I would spray the panels afterwards there would still be some gaps.
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Old 02-04-2024, 00:51   #3
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Re: Strange marks on Plywood after painting.

Quote:
Originally Posted by Fore and Aft View Post
Franziska that looks like small voids in the final plywood skin Nothing serious, but you could fill it with some of that polyester putty that cures in 5 minutes. When I used to paint plywood with epoxy undercoat, I would lay it on thick then spatula the paint into all the voids. Even then when I would spray the panels afterwards there would still be some gaps.
Cheers

Thanks, funny thing the panel was painted before but did not show this on the old paint (which is underneath).
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Old 02-04-2024, 01:27   #4
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Re: Strange marks on Plywood after painting.

Quote:
Originally Posted by Franziska View Post

I have one panel where I now see these marks in the photo. All other are OK. They appeared already during painting and kept coming back every time I rolled over them.

What is the reason (resin in the wood veneer??)?

What are the remedies (sand the area, filler with polyester putty and repaint?)?

Thanks for suggestions.
Looks to me like contamination or an incompatibility issue that has changed the surface tension of the paint in those areas.

Sand then filler, sand and repaint should fix it.
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Old 02-04-2024, 04:59   #5
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Re: Strange marks on Plywood after painting.

looks like fisheyes just longer streaks instead of a single eye.

I think Ballsnall is on the right track with some sort of contamination in that area.
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Old 02-04-2024, 15:21   #6
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Re: Strange marks on Plywood after painting.

Given the above posts, my guess is the plywood did have some small (clean) voids when first painted and the old paint skinned over the voids OK.

Later, some contaminate penetrated the old paint and entered the void. When you prepped the old paint surface, the contaminate in the voids were now exposed but not removed. The new paint didn't like the contaminate still hidden in the voids!
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Old 02-04-2024, 15:57   #7
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Re: Strange marks on Plywood after painting.

The paint was put on too thick and did this when drying, or a contaminant was involved.

And yes: Sand, Bondo, Repaint, and you should be gold.
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Old 02-04-2024, 16:01   #8
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Re: Strange marks on Plywood after painting.

Sand the area, PRIME and topcoat.

https://deutschcolor.com/en/product/holz-vorlack-180/
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Old 02-04-2024, 17:19   #9
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Re: Strange marks on Plywood after painting.

Contamination is a likely cause.

With the surface prep you've already done you will have removed or reduced most types of contamination.

Silicon residue is a possible culprit and very stubborn.

Try some drops of "Silicone Off", "Anti Silicone Drops" or similar product to the paint at next application.

Usually packaged in an eye drop style bottle.
You may have to ask for it at the paint counter rather than find it on the fixture.
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Old 02-04-2024, 17:44   #10
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Re: Strange marks on Plywood after painting.

Contamination. Was the original finish not paint? If so it probably had oils or waxes on it. When you sand it down, the contaminants get ground into the wood and affects the new finish. Always strip the original finish with a solvent before sanding if you are going with paint.
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Old 02-04-2024, 18:14   #11
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Re: Strange marks on Plywood after painting.

I agree with most who have responded, contamination. The “old paint” may have harbored the contamination now readily apparent. A pigmented shellac primer would have sealed the surface prior to the finish coat being applied.
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Old 03-04-2024, 03:50   #12
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Re: Strange marks on Plywood after painting.

https://www.kilz.com/primer#/ViewAllProducts
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