Antifouling Steel Boat

[zeseb]

I'd like to proceed myself for the antifouling of my steel sailing boat.
The previous owner used Altex no 5.

What is the best way to do it? Do you have to remove the old antifouling layers? How etc.

Thanks for your help.

[coopec43]

Zeseb.

Did you have a look at the makers of Altex No 5 recommendations? Do they apply to your situation?

Repainting: High pressure water clean (5,000 – 10,000 psi / 330 –
660 bar) to remove all marine growth, hydrolysed antifouling, salts,
loose paint and any other foreign matter.
OR: Low pressure water clean (3,000 psi / 200 bar minimum) to
remove all marine growth, hydrolysed antifouling, salts, loose paint
and any other foreign matter.
AND - Wet sand the surface with 80 grit sandpaper to ensure total
removal of any remaining contaminants, including residual
hydrolysed antifouling and slime. Rinse thoroughly.
The cleaned surface, once dry should be free of any powdered
antifouling residues and should be inspected for defects in the film.
Existing anti-fouling must be secure and intact, and not excessively
overbuilt.
Repairs to the coating system should be completed before the
application of any subsequent coat of antifouling. To ensure good
adhesion, any exposed primers / undercoats should be thoroughly
sanded (p80 grit), dedusted & coated with the appropriate primer
before application of any antifouling.
Thorough wet sanding is recommended at the waterline, as the wet
/ dry cycle and UV exposure can cause premature failure if brittle or
crazy cracked coatings remain.

https://www.nauticalsupplies.com.au/...ouling_PDS.pdf

Clive

[Fore and Aft]

If you are going to change antifoul brand at the very least you will have to put a barrier coat on like Primocon (International) or Vinny guard.
Altex No 5 works well here in Hervey Bay.
Cheers

[zeseb]

Thanks for your answer.

The previous owner put some Altex n5 hence my choice so I don't have to change it.

The sanding part is a bit confusing for me. When you sand it with some grit 80, what sort of finish shall I expect? Does the previous antifouling need being entirely removed or just sand to get a surface ready for the new antifouling paint?

Cheers.

[Fore and Aft]

I never muck around sanding the bottom with 80 grit. I use 40 grit on my random orbital and just key up the whole bottom and feather out any craters or loose bits. Really I am doing this as I do not want to much paint build up.
In the good old days we would just water blast the old mans trawler, roll on some new antifoul and back in the water. No sanding or prep.
Without seeing the bottom of your boat it is hard to know what to do. If it looks like a golf ball (lots of craters) then it might be time to remove all the antifoul paint.
Cheers

[zeseb]

I got a detailed answer from Altex which explains it all; I hope it will help other guys.


There are a couple of options available for you to consider regarding repairs to corroded areas, however if the areas in question are small and minor and can be mechanically cleaned (e.g. by us of a power tool grinder), a convenient system could be as follows:



- Low pressure water clean (3,000 psi / 200 bar minimum) to remove all marine growth, hydrolysed antifouling, salts, loose paint and any other foreign matter.

- Wet sand the surface with 80 grit sandpaper to ensure total removal of any remaining contaminants, including residual hydrolysed antifouling and slime.

- Rinse thoroughly.

- Spot power tool clean to AS 1627.2 St 3 all corroded and damaged paint areas. Feather back edges to existing sound coating.

- Clean to remove all dust, grit and debris.

- Spot prime all prepared exposed areas with PrimaShield Sealer

- Apply another two coats of PrimaShield to all previously spot primed areas whilst progressively overlapping existing coatings. Allow curing time between coats – Refer to TDS attached.

- Apply two full coats of No. 5 Antifouling to the entire hull below waterline area. Allow curing time between coats – Refer to TDS attached.

- Allow final coat to cure for a minimum of 24 hours before relaunching.