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MG Midget and Sprite Technical - Barrier paint

Painting celly over old 2K. I know they react, depending on which is the new coat application, just can't remember which is the problem order. Celly onto 2K, or 2K onto celly?
Or should I just use a barrier coat first? I will probably ask paint suppliers but suspect the correct answer can be got here.
GuyW

Guy, I have no personal experience with cellulose paint but my guess is that 2K over celly might give trouble.
2K can be very aggressive on some 1K paints...
A de Best

I'd try the celly on a corner or out of view place first and give it a few hours to see if the solvents react. I know that celly reacts on rustoleum combicolor but that isn't 2k of course.
Bill B

Haven't bought the celly yet, Bill. I need to order it but was wondering about buying a barrier paint at the same time.
GuyW

I think that, whatever anyone says, you can't be sure so I'd be strongly tempted to put a barrier coat on. Celly is expensive so you don't want to waste it plus all the extra hassle if it does react. Just my opinion.
Bill B

Yep, probably good advice Bill.
GuyW

I sprayed over 2k on my Capri.

No barrier paint.
No reaction at all.

My Capri had previously been resprayed in 2k, and after a fair bit of welding and banging about by me, it needed areas respraying.

1st I wiped it over with celly thinners. Then brush painted a small area. No reaction. Then I rubbed/flatted down the 2k on both front wings and sprayed them. No reaction. Then I did bith doors and most of the rear wings. No reactions at all.

HMG M99 gloss cellulose.

https://www.hmgpaint.com/products/classic-car/topcoat/122/m99-cellulose

anamnesis

I know one sequence is much more likely to react than the other - just couldn't remember which way round it is.

Considering the logic, I think if the older surface is 2k, and has been on a while, then the volatile component has evaporated off and the remainder is chemically bonded by the 2k process such that the cellulose thinner doesn't react.

Whereas, if the old surface is the cellulose, it will still soften and react with the thinners component of 2K applied over it as it is essentially air dried rather than a chemical bond. Complicated if the cellulose is very old and become chemically stable, but that cannot be relied on, especially as other contaminants can upset things too!

I know I have read this stuff before but my brain cell was looking for a second opinion.
GuyW

If you're definitely spraying in celly, you'll need celly thinners anyway. Buy the thinners, and see if you can disturb the 2k with it.

That's what I did, and as the 2k was completely resistant to the thinners, I already knew the celly paint, even 50% thinned, wouldn't be a problem.

Yep, what you say about paint age must make a difference too, but no matter how old it is, celly thinners will disolve and start to wipe of old celly paint.

anamnesis

This thread was discussed between 04/04/2025 and 06/04/2025

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