Is this clean enough to prime?

[lampshuk]

The antifouling flaked off quite badly when the boat was lifted, and the marina crew advised scraping back to gel coat, which i have done the hard way (paint scrapers, no stripper). I didn't see much evidence of a primer coat, but this is as clean as I can get it without shaving the gelcoat.
Is this clean enough to prime? I don't want to have to shotblast it.

I am planning to use a dedicated sander with gnarly wire brush on the keels to get the loose rust off, then genolite, lead oxide and primer.

Hoping not to have to do this again for 10 years or more!

 

[Sandyman]

For info:

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[lampshuk]

Thanks. Just edited the post. Should be better now.

 

[vyv_cox]

Paint adhesion problems are often caused by production wax or mould release agent on the hull. Provided you have removed it all your paint should stick well. A quick run over with an orbital sander with 180 grit should be the final touch. I would not use a wire brush on a cast iron keel, it tends to drive rust and debris into pores in the surface. An angle grinder is a far better tool for the job and will take little longer.

 

[pcatterall]

Looks OK to me provided that the yellowy greeny stuff is some kind of paint not slime!! If the primer goes on ok and doesn't pull off bits with the roller it should be fine

 

[VicS]

The antifouling flaked off quite badly when the boat was lifted, and the marina crew advised scraping back to gel coat, which i have done the hard way (paint scrapers, no stripper). I didn't see much evidence of a primer coat, but this is as clean as I can get it without shaving the gelcoat.
Is this clean enough to prime? I don't want to have to shotblast it.

I am planning to use a dedicated sander with gnarly wire brush on the keels to get the loose rust off, then genolite, lead oxide and primer.

Hoping not to have to do this again for 10 years or more!

Id expect to see a more uniform appearance of the grp when clean enough to prime. Traces of the old antifouling maybe but what the brownish areas ?
The finished job will be no better than the preparation you do now.

Is lead oxide a recommended primer for the keels ???

Ideally the keels should be grit blasted but failing that grind the metal surface with 24-36 grit abrasive discs to a uniform, clean, bright metal surface . Use an angle grinder on small areas.

Check for absence of salt using potassium ferricyanide papers if you can.

Prime without delay once prep'd

International suggest priming with Primocon, after pre-priming with thinned Primocon.

Lead oxide might require a barrier coat before antifouling is applied

I'd recommend that you down load the product data sheets and diligently follow the recommendations of your chosen coatings manufacturer

 

[lampshuk]

Thanks, all. I should probably have mentioned that the boat is 25 years old (Moody31) so goodness only knows what the brown stains are. They don't come off easily, though, so I'm going with "ancient paint" as a best guess. There is a fair number of gouges here and there on the hull, so I will spot-treat with gel coat filler (I have some Plastic Padding in the toolbox to use up) then run over it with a sander as you suggest, Vyv.

As far as the keels are concerned, I must admit to being a bit torn. The anti fouling and paint in general (there seem to be many layers, including one that looks a bit like copper) seems to have stuck better there than on the hull, and I am rather a fan of the "if it don't come off easily, it's probably OK to leave it be" school, so I will play it by ear. Thanks for the tip about the angle grinder, Vyv. I have one of those too, so will put it in the mix.

VicS, I am afraid that I have chosen the budget approach to paint selection, going with the Gael Force primer and anti foul (the AF was on special offer, so what else could I do?) and the instructions are pretty basic. I read the PBO review of AF and came to the conclusion that the only deterministic thing about the different paints was the amount you paid for them (did anyone else read that? I seem to remember that their "best buy" selection was about 4x the price of one that got subjectively similar results).
Anyway: the GF primer says it sticks to just about anything. Including, I hope, lead oxide.

Having said that, I need to look at the paint I have in mind as a sub-primer. It may not be red lead. I seem to remember that it is red-ish, though.

Thanks, all. I will keep you posted. If it all washes off by July you will be able to hear my anguished cries the length and breadth of the Solent.