antifouling, new over old. Primer.

[jack daniels marine]

Hi folks,
I have a 2005 fibreglass boat, 19 ft. The boat is used in seawater, but is moored in a fresh water river when not in use.
When newthe boat was coated with 2 component primer and self polishing antifouling.

however after that it looks to have had another coat of primer , probably a coat or two of self polishing, and a coat of hard antifouling on the top. The very top coat has been painted a few inches higher up than the previous coats to raise the water line, without primer.

Now I have scraped off allmost all but the original 2 component primer with Owatrol marine stripper and a metal scraper, there is still quite a lot of blue from the very first coat of antifouling, but the surface looks good and suitable to just paint over

There a quite a lot of scrape marks into the original primer from my metal scraper. Both the fibreglass and primer are white.
My question is, should I now use 2 component primer for the best protection against osmosis, or 1 component?

Some say more 2 comp primer will disolve whats on there and make it worse. Some say that 1 comp may not be enough to protect small scratches into the gelcoat.

I guess I need to buy 2 comp anyway to raise the waterline a few inches at the front.

 

[Home Cookin']

Re: antifouling, new over old. Primer.

paint over it with anti fouling; skip the primer. spot prime the scratches if it makes you feel better but the top coat of paint will take care of it.
next time just paint over it.
My concern would be that your chemical stripper will affect the bond of the next coat. Too late now.

 

[oldboat1]

Re: antifouling, new over old. Primer.

what Home Cookin' said. Use some mineral spirits or lacquer thinner over area where stripper applied (water if water wash stripper), then sand with wet/dry or hit with a plastic scrubber. Then hit it with the anti fouling paint.

 

[Arkyhunter46]

Re: antifouling, new over old. Primer.

If you stripped it with a chemical stripper I would use a tiecoat primer between the original primer and the new anti foul. I also recommend sanding the entire bottom before painting. The difference between a paint job and a bottom job is the prep work. Taking the time now to do it right will save you cash later. Tiecoat will bond with any marine antifoul and covers in one coat. Sand with a rough grit scratching the surface evenly. Wash boat with water and let it dry completely before applying tiecoat primer. Allow a day between coats.

 

[jack daniels marine]

Re: antifouling, new over old. Primer.

thanks ya'll for the good advice.
The Owatroll marine strip seems to be very mild, not particularly effective, though I used it at 42 deg.F

So to sum it up, the small scratches from my paint scraper are nothing to worry about then?
I'll use one of those fibre mat type scrubs to smooth it all off, and then wet sand with 180-220.

I plan to use Hempel NCT ( replacement for mille ultimate ) antifouling. A good wash with Hempel preclean degreaser is specified prior to a new coat.

 

[Chris1956]

Re: antifouling, new over old. Primer.

80 grit paper is sufficient, and will be a lot faster. Two coats of antifouling is necessary. Is Hempel an ablative antifouling paint? If not I would recommend a multi-season ablative. You will get two years out of a paintjob, maybe more.

 

[jack daniels marine]

Re: antifouling, new over old. Primer.

Ablative? I had to look that one up in wikipedia.
Yes it is self polishing, good for boats up to 40 knots.
There are probably other products as goods as or better, however the original coating from the factory is Hempel.
Hempel is probably the top seller here in Scandinavia.

here's the product datasheet:
http://www.hempel.dk/product-list/p...eName="PDS HEMPELS MILLE NCT 71180 en-GB.pdf"

 

[Chris1956]

Re: antifouling, new over old. Primer.

Jack, For some reason here in the US we have single season ablative antifouling paint and multi-season ablative A-F paint. I would recommend the latter.

 

[jack daniels marine]

Re: antifouling, new over old. Primer.

they are not really marketed as single or multi season here, however some product datasheets do say protection for 2 years instead of the usuall "protects the whole season long".

I dont mind having to put on another coat next year. It's scraping off the mismatch of various old layers that I dont want to have to repeat. There's no growth on the hull at all, the coating just wears a bit due to friction.

What I do notice in the datasheets I have seen is the speed rating, many are good for <20 knots or up to 25-30knots. Not so many self polishing products are good for 40 knots. Maybe a 40 knt. product at low speed will last 2 yrs.