What The????

[galleywench]

I just finished up a 3 hour date with a long board, 6" orbital sander and a whole bunch of 60 grit paper and I'm pretty disappointed in what I ended up with.
I thought that this section would be easy; it's the forward cabintop around the mast step and is the only section that didn't need a full recore. There were 4 or 5 small sections of bad core which I replaced and quickly knocked down to a reasonable fair, and thought the rest of the section would just be a matter of hitting it with the orbital sander to knock off the paint and get it ready for primer.

In reality however, the paint on this section was tough; I mean really tough. I really couldn't get through it with 60 grit paper unless I angled the sander on edge into the stuff (which doesn't make for a fair deck). I can only assume that this is some sort of LPU paint and not a 1 part enamel.

So the question is: Assuming this is a 2 part LPU can I use it as a substrate for my primer (Interlux primekote followed by perfection) or do I have to remove all of it to get a good bond? I'm really sick of sanding this stuff, but I'm not willing to risk the longevity of the new paint because I cut corners.

Any help appreciated, the picture is after sanding for WAY too long.

[Tallystick]

Angle grinder with flap disk or wire brush, or belt sander with 36 grit would get through the paint way faster. Contact the manufacturer of the paint you'll be using to see what they say about the need to remove the old paint.

[galleywench]

I did talk to the Interlux rep. and they said "it depends". You can apply 2 part over 2 part but it is condition dependent and I'm not certain that it is 2 part paint (although I don't know what else it could be; it sands like granite). Is there a way to definitively tell if the original paint is a 2 part and does anyone have any experience painting over it?

I'm hoping I can avoid the angle grinder. I spent far too much time with one last year when I was grinding bevels in the decks; it's so messy that I'll probably have to have the EPA come in and declare my boat shed a superfund site once I get the boat out of there. It was not a pleasant experience.

[Carl-A259]

Have you considered using a paint stripping agent?

[galleywench]

I hadn't considered that, I was under the impression that paint strippers could soften the underlying fiberglass and have avoided them. I don't know where I heard that so I'm not sure it's true.

[hriehl1]

While I'm no chemist or paint expert, it does seem to me that any coating that resists the mechanical attacks you've levied thus far is well-adhered. So the operative question becomes will the PrimeKote you want to put over top of that tough stuff adhere to it? I am a big believer in primer. And if you rough up that substrate to give it some tooth, I'd be very surprised if the PrimeKote doesn't adhere; after all, a primer's very purpose of to improve adhesion both above (finish coat) and below (substrate).

After a first coat of PrimeKote over that stuff, give it time to cure then do some destructive testing with a knife blade or scraper to see if you detect lesser adhesion over these areas than on bare gelcoat. If adhesion seems comparable, I'd assume you're good-to-go.

Good luck. Hank

[galleywench]

Thanks for the help, I contacted the interlux rep again and he told me to do something similar, it's called an MEK test (Methyl Ethyl Ketone - I think it's in brushing thinner). The process is to soak a small rag in it, place it on the surface in question and tape a plastic bag over it (so it doesn't evaporate) and leave it for 24 hours. After that, pull the bag and see if the underlying surface has softened up, cracked or bubbled. If not your good to go with primer.

My primer and brushing thinner should be here on Monday, so I'll find out then. Always lots to do in the meantime.