Removing old antifouling

[kilkerr1]

Please don't tell me we need to do this, please, please...

First winter's work on the boat: after blasting the old girl's bum with our new pressure washer thing (great fun, and most impressed to see only a smattering of tiny critters and slime attached to the hull - guess this is 'cos she sits in the mud for 20 out of every 24 hours..?) we're now wondering whether we need to get rid of all the old antifouling before anything else. All advice gratefully received. Except, of course, the advice which says 'You need to scrape all the old paint off'.

I've searched previous posts and found what I can, but not much mention of when/how often one should do this.

Please don't tell me...[repeat as nauseam]...

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[Robin]

Is the old stuff still stuck on, is it still fairly smooth, how many years of it is there, do you know what it is???

If it is flaking off or if there is 'n' years of stuff especially hard stuff then ideally it should come off.

If you know what it is, and it isn't too bad then you can check with the manufacturer of the paint you plan to use if it can be overcoated. Often it can be overcoated, either directly or with an insulating coat (International use Primocon primer for this) in between.

At the very least, remove any flaking stuff, rub down with wet/dry (wet) to smooth edges and give a key for the new paint.

Nice job to look forward to, especially laying on your back in a puddle between bilge keels! Have fun....

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[AndrewB]

No, don't bother unless you are seriously racing your boat or there really is a huge build-up of old paint. Eroding antifouling wears itself thin and it takes years for a bad build-up to develop, with a lumpy, irregular surface. With a bilge keeler the worst place is always between the keels because the difficulty of cleaning and painting there tends to result in a slapdash effort year after year.

The pressure hose will have removed any loose paint. Normally the old surface will take new compatible antifouling without any further preparation. If you are really keen you can sand it smoother before repainting, but don't forget the dust is toxic so great care is needed.


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[claymore]

Don't bother now - repaint it and see what it looks like next winter -(and how it sails this year)

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Claymore
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[kilkerr1]

Oh gawd bless you all, will slap some more, er, slap on her and see how we go this season.

V happy. Thanks. /forums/images/icons/smile.gif

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[macd]

Should anyone have the misfortune to have to remove their anti-fouling, a couple of tips:

buy a Bahco scraper with a 50mm blade (B&Q stock 'em): the best tenner you ever spent.

Really stubborn antifoul can be softened with either expensive stuff from International, or cheap home-made gloop. Dissolve caustic soda crystals in water (add the crystals to the water, NOT vice-versa), then add cheap wallpaper paste to stiffen the mix so it won't run off the hull (similar consistency to Nitromors paint stripper). Apply, go to the pub for a couple of hours, then scrape. Goggles and gloves a must. This stuff does not damage gelcoat.

But it's still a horrible job.

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[machurley22]

How much caustic soda to how much water?

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[happychap]

seems like a great alternative to Nitromors - what ratio for stripping paint? presumably the paste will be to suit the surface being worked on

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[macd]

Concentration of caustic soda to water: the strongest mix described on the package (plus a bit for luck).

You'll probably need less wallpaper paste than you imagine. It tends to sit there doing nothing much for a few minutes, then thickens up suddenly. You don't want the consistency of porridge.

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