bottom paint

[donelanc]

Hi
I have a 272 oday 89 and am re doing the bottom paint. According to the two previous owners it hasn't been done in 20 years; just touched up. I notice a lot of white spots but was told they were probably from barnacles; no oozing, hard, smooth. I'll sand 70% off the bottom. The old paint is black and hard; doesn't come off on your hand when you rub it. What would be the best bottom coat to put on this; (don't want to do a barrier coat unless someone really thinks I need it. Appreciate any advice.

thanks
Paul Donelan

 

[rajhnsn]

Barnacles can leave a white spot. If you are seeing bumps under the paint you should break them open with a tool to see if they are blisters in the gel coat. Only way to truly tell if they are blisters is to remove all of the paint. It can be done by scrapping with a sharp scrapper, chemically or soda blasting. Another option is to lightly sand what you have and add another coat of bottom paint. Most paints will adhere to most other bottom paints. If you are just looking for growth protection you could buy a relatively cheap paint and give it a try.

 

[donelanc]

white spots

Barnacles can leave a white spot. If you are seeing bumps under the paint you should break them open with a tool to see if they are blisters in the gel coat. Only way to truly tell if they are blisters is to remove all of the paint. It can be done by scrapping with a sharp scrapper, chemically or soda blasting. Another option is to lightly sand what you have and add another coat of bottom paint. Most paints will adhere to most other bottom paints. If you are just looking for growth protection you could buy a relatively cheap paint and give it a try.

Thanks for getting back Rajhnsn. It is white spots; not raised; hard as rest of finish; seems the barnacles took gelcoat with them. Do you think just putting on bottom paint will avoid osmosis thru these white spots? thanks for responding.
Paul

 

[ccarmody]

Do you have any pictures? Barnacles can leave a white spot but often it's the bottom of them after the top has been pressure washed off. If it's blisters it probably will not be white (if the paint is intact) as it will be swelling under the gel coat and just push outward. See below, take a pick to it to confirm (this is from a bad keel repair from the PO on my boat) -

 

[SailingCal21]

Are the white spots below the surface of the bottom paint? Pictures would help.

If the paint came off with the barnacle I would expect that the existing paint to not be adhering very well.

ccarmody, it looks like you have a link to a pict at the end of your post, but can't select it.

 

[ccarmody]

 

[fstbttms]

Do you think just putting on bottom paint will avoid osmosis thru these white spots?

The short answer is, "No." Anti fouling paint is not waterproof. Quite the opposite in fact. It is designed to let water penetrate it. That's how the biocide gets out. It will not eliminate osmosis.