antifoul

[robmann]

I have small patches of antifoul that have flaked.? The boat has not been in the water since the last owner antifouled, He antifouled on top of the old antifoul he did not strip it back to the gelcoat first. Can i just paint the flaked area, Or paint over all the antifoul, Or remove all the antifoul back to the grp and start again.
Rob /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

 

[Guest]

It is standard practice to antifoul over the existing. Waste not... General way is to abrade back the antifoul to get back to a good solid antifoul. Can be done with a two handed scraper!

However this country is just not setup to sand safely. In other part of the world the yards hires out wet sanders driven by air, or dry sanders with industrial vacuums to avoid heath risks to others. They insist that everyone use the supplied equipment. Nominal charge.

Still need to have personal protection because wet or dry antifoul powder is dangerous. Wet it takes your skin off and dry it takes the inside of your lungs away.

So in most cases you pressure wash it and then hope the next layer will stick. International just say scrape and wash. A good modern jet washer does do a good job of getting under any flaky areas and removing the soft top layers. Last time I did it I had to hand wet sand the lot!

http://www.international-marine.com/antifoulings/application.pdf

http://www.yachtpaint.com/Images/29_20471.pdf

 

[Spuddy]

Several points here:
No need to go back to gel coat when antifouling. Poke around with a scraper and remove any loose patches.
If any gel coat shows through then dab with a primer - Primacon or similar
Some antifouls need to be in the water within a few weeks of applying. If you don't know the type then best to do the lot again - previous owner may have antifouled so boat looked nice for punters.
DO take precautions when preparing surface. Wear protective goggles and mask if you are not ancient and diseased like me. Basic precaution though is to use wet/dry paper to rub down, used wet so toxic dust doesn't get into lungs.
On last point - wet dust will fall to ground, dry out and then be blown by wind into the orphanage for disabled kiddies next door which has recently begun to puzzle me but I still do it.

 

[alan006]

If you use a good high pressure washer on the old antifoul it should take off the loose stuff and whats left you can paint on top off. As "Spuddy" says Primacon is great for two reasons, it gives a key for the new antifoul and also stops any problems of reaction between different types of antifoul. If in doubt the antifoul manufactures are helpful as to which products will react with each other.