Problems with Red-Oxide paint

[donncha]

We used red-oxide paint as an undercoat/primer on the keel and the hull below the water line recently after scraping all the old paint off. It worked fine on the keel which is cast iron and appeared to take very well to the hull. The problem arose when trying to paint over it with anti-foul. On the hull which is pitch-pine the anti foul bubbles and lifts off when dry. The anti foul works fine on the keel. We tried painting over with an undercoat after removing the anti foul but the undercoat bubbles up same as the anti foul. Any solutions to the problem short of removing the red-oxide completely? This would be next to impossible at the moment considering we are going back into the water in 3 weeks.

The paint we used is called syn-oxide and it's produced by an Irish company.

 

[alan006]

I don't know if it will work in your case but Primacon by International is a great barrier coat between paints that react together. Why not try a small test patch and see if it works.
Best of luck with it.

 

[donncha]

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I don't know if it will work in your case but Primacon by International is a great barrier coat between paints that react together

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As it happens that is the undercoat we used, it blistered up and peeled off.

 

[misty56]

Interesting that you have a different reaction on the two substrates, which tends to suggest that there's an imperfect bond between the primer and the timber in the first place. Was there anything on the wood that might have caused this? Paint incompatibility is a real pig, you get lifting in patches, or some areas are fine at first and exhibit problems later--anything in fact to b*****r the painter up, but if there's absolutely no lifting over the metal, that tends to confirm the problem is with adhesion to the pine.

Sometimes a paint will soften due to the solvents in the overcoat, but the fact that it softens doesn't necessarily mean it will blister; however if there is already an adhesion issue then this can aggravate it and cause blistering.

With solvent incompatibility problems, IME the damage is often like what happens to paint when you put stripper on it, it gets that "Wrinkly skin" look and then lifts. With adhesion problems the paint tends to lift in patches without roughening the surface, or at least, not so much.

I have not used that particular barrier coat but usually these are pretty inert, so that tends to suggest a poor bond between the oxide and the pine as well. If that's the case it's hard to see what other cure there is than removing it.

I hate to say it but a lot of modern paints contain solvents that are really pretty aggressive and are not formulated for use on wood (they may say "suitable for use on wood" or something like it but that's not quite the same thing.)

 

[trouville]

Red "oxide" what??Iron oxide??

I always painted my hulls with red lead paint then either the barrier primer or the antifouling direct apart from one time all was ok.

The time my antifouling came off was when i used some very old blakes tiger over old hemples as id run out of the new AF!

An "Irish oxide" dosent sound promising what is it??

Three days is bags of time to get the stuff off and repaint.I used a heat gun and mask with carbon filters & always worked up wind when i could rotten work but a heat gun will get it off progressively

If its lead oxide then it will withstand the heat.Some will soften & come off but the rest will have to be sanded!!That is a bad job!!!First strip a small patch with the heat gun & try applying barrier primer on one part and AF direct on another,leave it overnight while stripping the restAfter the heat gun you may not have to sand.

Good luck

 

[donncha]

It's Iron oxide just to clarify. We talked to international and they said that because it is a white spirits based paint problems will arise. The guy I was talking to said that you could use the over the waterline undercoat instead the underwater one and it will work, but that he shouldn't be telling me this.

 

[misty56]

I'm getting confused here. What is the thinners for the syn-oxide paint? Is that the one that is white-spirit based? If so you must use a white-spirit based or acrylic barrier coat over it.

Generally speaking paint solvents should get less aggressive progressively, not the other way round. In other words if you clap a paint thinned with toluene (smell it) over one thinned with white spirit, you'll get in trouble, but, given sufficient time for the solvents to leach out of the first coats, white spirit will go over toluene no probs. Mostly.


Just out of interest, is that syn-oxide any good? (I mean apart from this case.) It's certainly cheap enough.

 

[alan006]

I'll be very interested to hear how you get on with the other undercoat that the International expert recommends.
Good luck.

 

[donncha]

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I'm getting confused here. What is the thinners for the syn-oxide paint? Is that the one that is white-spirit based?............Just out of interest, is that syn-oxide any good? (I mean apart from this case.) It's certainly cheap enough.

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White Spirit is the thinner for the syn-oxide. The syn-oxide seems to be pretty standard iron-oxide paint and it does it's job. It is really meant for metal but it seems to be pretty good on the wood as well. I managed to go over it with the international undercoat (above waterline stuff) and it seems to be holding very well. I'll sand down the little bits of anti-foul left and undercoat with the international and then anti-foul once again, hopefully this should do it. Thanks for all the advice.