bottom paint

[banshee]

how extensively do I need to scrape and sand the bottom of the hull - I am using the ablative antifouling paint and the hull is in pretty good shape

[Faster]

It depends on what paint you are planning to use and what paint is already there. If the paints are the same type and are known to be compatable, then a thorough wash (get rid of all slime) and a quick scuff sand should be fine.

If you don't know for sure what's underneath, it may be best to remove all old paint. Worst case scenario is your new paint could fall off after basically dissolving the old.

If you have several seasons of accumualtion you may want to get rid of it to avoid having too much paint there.

With ablatives it's a neat idea to have the first coat in one colour, and subsequent coats in a different color. That way when you are wearing thin, the original coat is exposed before you get through all the effective paint, and you know it's time to redo.

[sailingdog]

If you don't know what kind of paint is on the bottom... definitely sand it all off...just to be safe.

Otherwise, what Faster said is pretty much spot on.

[banshee]

it is definately ablative - i put a coat of ablative over it and i am all set - one question - when i put the new paint on - when I loaded up the roller (too heavy I think) when applying it, the old paint flaked off - this was only in a few spots - i think with too much paint on the roller the moisture in the paint loosened the old paint - it was adequately sanded - just that the ablative nature of the old coat did what it was supposed to - flake off. in the end it just made for a rougher than ideal paint job - I may sand down the new paint and apply another coat in those spots. comments?

[Freesail99]

Last year while sanding off the paint on my bottom, I got an infection when some of the copper paint fell into a small wound on my leg. It ended up being a 5 day hospital stay fighting that infection. Wear a paper suit, gloves and a respirator.

[sailingdog]

Yes, you definitely want to wear the bunny suit, gloves, goggles and a dust mask or respirator.

[banshee]

any comments on the flaking problem/situation?

[Freesail99]

If your bottom is flaking, the paint must come off.

[Bill Mc]

This is the Tumbleweed with her fine new bottom. If the paint is flaking you'll have to sand. Remember that this is a biocide so wear a respirator and protective clothing.

Fair winds,

Bill

[sailingdog]

If the paint is flaking, and you sanded it prior to painting, it usually means that someone along the way before you did a bad prep job, or that there are just too many layers of paint on the bottom. Paint only sticks to what ever is just beneath it.... and if you get enough layers, the inner layers won't be able to support the outer ones...and will flake off.

Sanding the hull down until you get to the gelcoat is one way to insure that whatever you apply will stay stuck. But if you go down to the gelcoat, you'll probably want to barrier coat or prime the bottom before continuing.