New layer of antifoul paint seems to have caused reaction

[who4ever]

This is my second year with my Osprey, and the first spring I had her bottom painted.  I hadn't been in the water for 2-3 weeks, when I saw that some of the bottom paint that is above the water line had chipped off from the hull.  I had my marina pull the boat and I was stunned.  The boat looked like it had leprosy.  Hundreds of 1-2 inch areas of paint had fallen off, taking with it various layers of old paint.  In some areas, I was able to scrape the paint down to the gelcoat.
My mechanic gave me some double talk saying that after a certain point, the new layer won't hold, and everything has to be sandblasted off and start from scratch.  That may be true, but it didn't explain why the boat looked much worse than the end of last season.

Has anyone ever heard of a bad reaction between new bottom paint and the old layer?  Should this have been patch tested first by the mechanic?  I feel that for a lousy $200 coat of paint, I am going to be facing a few thousand dollars of work.

Dave

[gran398]

The new was applied to the old,  the old released and the whole mess is peeling off in splotches, correct?

Remove it all and repaint. Strip and start anew. The old mung will be gone. Boat will look and run better too.

2K? No way. The running surface can soda-blasted for 300 bucks or less. Dry out thoroughly, then new bottom paint straight on the stripped gel.

Sand if need be, but the soda-blast should leave it rough enough. No need to hide imperfections/get pretty...it's bottom paint.

Screw the yacht yard....take it to a reputable soda blast outfit and make it happen. Then tape it off and get a local hard-working kid to paint the bottom with the paint of your choice.

[wingtime]

After a few coats the bottom should be sanded down before repainting the bottom.  It is possible the new paint reacted with the old...   but more than likely the old original paint has just started to flake of taking the top layers with it.   Don't sand blast it  that causes way too much damage to the gel coat...  have it soda blasted.

[RickK]

I wonder if the wrong kind of paint was put on over the existing paint?  Like a "hard" bottom paint over an ablative existing paint?  I think you can put an ablative over a "hard" existing paint but not the other way around.

[who4ever]

Thanks to all for your time to respond