(12-09-2012 11:44 AM)BottomPaintStore Wrote: The best thing to do would have been to sand the existing coating with 80 grit sandpaper to remove the oxidation on the old coating. After the sanding, you would just need to rinse of the residue with water and let it dry before painting with a new coat. When you put on a new coat of paint, the adhesion of that coat to the previous coating depends on a couple of things.
1. You should make sure that you give it a good 80 grit sand and rinse properly as described above. No solvent wash!
2. Longterm adhesion depends on how many previous coats are on the hull. If there are several layers of old paint, the new coat will soak through and lessen the adhesion of the underlying coats. This is due to the solvent penetrating through to the underlying coats and may cause them to let go and peel off. So if you have several layers, it is wise to due a thorough sanding to remove some of those old layers. You saw this first hand with your solvent wash!
Interlux does say not more than 60 days, but you can extend this significantly by pressure washing the boat (lightly) before you launch the boat. The reason why the say 60 days is because the paint will oxidize and that chaulky outer layer will have limited antifouling characteristics. With a light pressure washing you will remove that oxidation and expose a fresh layer of paint with good antifouling characteristics.
Be sure to put on at least two coats of paint... The paint you are using is designed to wear away overtime. The pressure wash will remove paint, so you need to make sure you have enough paint on there to withstand the pressure wash and get you through the season!
Thanks a lot mate. That answers my question.