Sanding Barrier Coat

[shamrock]

I'm stripping the bottom paint in preparation for a barrier coat and the gel coat is either slightly crazing, or is just gouged from when sanding to prep for the original bottom paint with a disk sander.

Can I stop sanding when all the paint and pigment is gone, or should I keep sanding through the small cracks ( see pictures)

I am using a random orbital with 80 grit.

thanks

[shamrock]

Sorry, I'm not sanding a barrier coat, I am sanding off the antifouling in preparation of a barrier coat.

thanks

[David M]

The anti-foulant paint has to come off but you can paint over gelcoat that has been roughened up by sanding, is clean and is not loose. I like Interlux 2000. You can get it in grey or white. It has to go on in a number of coats to be effective.

[delmarrey]

Originally Posted by shamrock

Can I stop sanding when all the paint and pigment is gone, or should I keep sanding through the small cracks ( see pictures)

I am using a random orbital with 80 grit.

thanks

Don't worry about cracks or scratches. The barrier coat will fill and seal them over.

[minaret]

If those are actually cracks or crazing then the gel coat needs to come off, as it is failing. But it looks more like scratches from a big disc sander to me. Hard to tell from these pics.

[donradcliffe]

If your cracks are random, you need to peel the failing gelcoat off. From the photo, it does look like they were machine-made in good gelcoat, so you don't.

[Phil Turner]

Get someone with a moisture meter that knows how to use it before you do anything else. On most boats with 20 year old(and some even newer ones) the gelcoat is porous and the laminate is wet which would require peeling. Phil Turner

[shamrock]

Thanks.

The scratches are mostly from a sander and in places there is slight crazing. It seems where the gelcoat is crazing it is also relatively thin and It is coming off pretty easily with the sander, so I am sanding right through it for the most part.

Will do with the moisture meter. trying to track one down to avoid buying one.

[clockwork orange]

You need to determine if you are dealing with crazing or sander marks, it is hard to tell from the photos. If you have crazing it needs to come off but that doesnt mean the whole bottom,just the crazed areas. Barrier coat is just a paint full of solvents which evaporate away on curing and WILL NOT take care of crazing. I personally have a boat with bad crazing and i will be peeling it next summer. It bears mentioning that in the areas where you go through the gelcoat you need to seal the raw glass with proper 100% solids epoxy before applying the "barrier" coats. You dont need to use the epiglass resin that interlux pushes for this purpose, any epoxy such as West or Systems Three will do the job the same.

Steve