Antifouling - whether to strip down old paint instead of painting another layers?

[MM5AHO]

I often wonder what the attraction is in removing antifoul. If you're racing then reducing weight and having a smooth hull is a good idea and so removal before reapplication seems sensible.
But if you're a cruiser, then why do all that work? Why not just pressure wash the growth off and put another coat or two on top?
I've recently taken mine back to gel coat, but only in order for a complete repainting above and below waterline. But until I started that job last winter with scraping, and had it done by a blaster to complete this year, its had 42 years of applications without total removal. Never really had any fouling issues, but should not do so with several mm thick antifouling.

 

[lpdsn]

Having a smooth hull does make a difference - to pointing as well as speed. And if you tackle the build up each year you avoid having to scrape the whole lot off when the surface starts to flake.

All depends upon your priorities of course.

 

[NormanS]

With my old wooden boat, which was usually antifouled between tides, she was brushed off, washed, hopefully dried and another coat of antifouling slapped on. It was never scraped off. Imagine trying to scrape the bottom of a 60' boat between tides!
The result was that it got to the stage when the roller applying the paint was tending to take off bits of the old paint - not a happy situation.

Our new (to us) GRP boat was heading the same way, and we had her bottom slurry blasted about ten years ago. Since then we apply a single coat of copper antifouling each year, but to avoid any build-up, we wet sand her bottom every year, using the long handled device mentioned previously. There is no build-up of paint, and her bottom is as smooth as the proverbial.

 

[johnalison]

My boat suddenly went much much faster after stripping and renewing the bottom, just as my car goes much faster after a wash.

 

[Tranona]

I think my bottom will be slightly less pocked than yours. I figure whilst she's out, give it a light all-over touch with a power sander, then get the antifoul rolled on. Hopefully just a one day job . As it's not utterly critical, I reckon I'll not even bother asking the yard to move the chocks once its dry (though mayyybe i'll have a brush ready when they're lifting her back in, I think it's rapid-dry).

Please do not use a power sander on antifoul. It is nasty stuff and as others have said on this thread it needs to be either blasted under controlled conditions, dry scraped and all residue collected or wet sanded.

 

[Lucky Duck]

Having a smooth hull does make a difference - to pointing as well as speed. And if you tackle the build up each year you avoid having to scrape the whole lot off when the surface starts to flake.

All depends upon your priorities of course.

This

I try and wet sand the remains of the last season's coat off before putting the new stuff on.

 

[Bobc]

I often wonder what the attraction is in removing antifoul. If you're racing then reducing weight and having a smooth hull is a good idea and so removal before reapplication seems sensible.
But if you're a cruiser, then why do all that work? Why not just pressure wash the growth off and put another coat or two on top?
I've recently taken mine back to gel coat, but only in order for a complete repainting above and below waterline. But until I started that job last winter with scraping, and had it done by a blaster to complete this year, its had 42 years of applications without total removal. Never really had any fouling issues, but should not do so with several mm thick antifouling.

I don't get it either. I guess they have too much time on their hands, or maybe the "dry January" means they have to find something to keep their minds off the beer.

 

[NormanS]

I don't get it either. I guess they have too much time on their hands, or maybe the "dry January" means they have to find something to keep their minds off the beer.

If you had had old antifouling flaking off on your roller when you were applying the new stuff, you would understand.

 

[Bobc]

If you had had old antifouling flaking off on your roller when you were applying the new stuff, you would understand.

Just scrape any loose stuff off and then slap some more on. That's what I do.

 

[MM5AHO]

If you had had old antifouling flaking off on your roller when you were applying the new stuff, you would understand.

I always pressure washed mine (higher pressure than yard anti-slime washer). That removed anything not well adhered. Allow to dry and apply new.

 

[NormanS]

I always pressure washed mine (higher pressure than yard anti-slime washer). That removed anything not well adhered. Allow to dry and apply new.

Yes, that would be the answer. However with an old wooden boat, a pressure washer has to be used with great caution. It's all too easy to disturb the caulking. Anyway, I was doing it between tides at an old stone pier with no facilities. I USED to think that wood was good.

 

[davidmh]

I usually just patch the bits that flake of as others have said. I have a question on the best abrasive to use to blend in the sharp edges of the area to be patched. Should I -
Use a coarse grit paper say 40/80 dry, I dont like this with the problems of dry dust
Use a wet and dry paper, used wet, the coarsest grit I can find is 120 is this too fine, can you get 80 grit
Used a scouring type pad, used wet, the domestic type scourer is ok for general cleaning of the antifoul but is not abrasive enough for removing much antifoul. Is there a courser more robust industrial grade scourer.

Any experience of doing this would be very helpful

Regards

David MH

 

[Slowtack]

I used this type of scraper, very efficient but grind off the blade corners first to avoid gouging the gelcoat
https://www.amazon.com/Bahco-Premium-Ergonomic-Carbide-Scraper/dp/B000288LP6

 

[Pye_End]

I usually just patch the bits that flake of as others have said. I have a question on the best abrasive to use to blend in the sharp edges of the area to be patched. Should I -
Use a coarse grit paper say 40/80 dry, I dont like this with the problems of dry dust
Use a wet and dry paper, used wet, the coarsest grit I can find is 120 is this too fine, can you get 80 grit
Used a scouring type pad, used wet, the domestic type scourer is ok for general cleaning of the antifoul but is not abrasive enough for removing much antifoul. Is there a courser more robust industrial grade scourer.

Any experience of doing this would be very helpful

Regards

David MH

Use sanding mesh, such as https://www.toolstation.com/shop/Pa...Prodec+Advance+Sanding+Mesh+115mm+x+5m/p41259

with something like this: https://www.screwfix.com/p/aluminium-hand-sander-84-x-240mm/12688

and do it wet.

Standard wet and dry cogs in no time, but mesh does not. Hose with spay head in one hand, mesh in the other. By far the best alternative I have found for your health and your time.

 

[Spirit (of Glenans)]

Not if you're using enough water. You rinse your hands in the bucket everytime you wet the scourer or squeeze the sponge so there's only traces get on your hands and arms. Worst thing is wet cuffs, so you need your arms bare up to the elbows.

Vet's long rubber gloves?

 

[davidmh]

Thanks Pye End, The Toolstation mesh sounds like a good idea, I will give it a go.

Regards
David MH

 

[B40]

I found it gave the best results if I painted the patches with Primocon, then carefully sanded the sharp edges to feather them off and putting on another primer coat on the patch. The result was hardly visible after antifouling.

johnalison, Please confirm: First, Primocon, then sanding, Primocon again and finally antifouling.
Read more at http://www.ybw.com/forums/showthrea...f-painting-another-layers#McoASQhvVMu5jktZ.99