bottom paint

[rharris8]

I have a 15' 1960 Herter's runabout project.
What is a good bottom paint, over fibreglass, for inland lakes? What about 2K automobile urethane?

[marshmat]

Is this a trailer boat or does it sit in a marina? If it lives on a trailer, you don't need antifouling at all. If it's in the water all year something like Micron or VC17 (both by Interlux) might be a good idea to keep the algae and slime at bay. Be careful to make sure you pick an antifouling that works in freshwater, and make sure it is of a type that can be taken out of the water (with some you can't take the boat out for long once it's been launched in spring). And keep this stuff below the waterline 'cause it's kind of ugly when dry.
Again, if it lives on a trailer, you don't need antifouling, just use the same type of paint as you would for the topsides, if you need to paint it at all.

[rharris8]

The boat (under restoration) will likely stay in the water from Memorial to Labor Day at my cottage, stored outside the rest of the time. The deck will see a cover but probably not much of the hull, as stored. There is a lot of minerals (iron, calcium) in the lake, being spring fed and there are now zebra mussels. I want a black bottom paint, due to mineral staining (plus it was original to the boat). I'm an engineer at Ford - the best automotive repair material is currently isocyanate catalyzed urethane, which I have ready access to, but I understand that a hull sitting in water is a totally different environment from your car sitting in the driveway, and I don't want to be at it again, next year.

[gonzo]

You need some kind of antifouling paint. This is a toxic material that kills any marine life form trying to attach itself. Soft-ablative-paints are easier to reapply and touch-up. They are soft paints where the surface wears off and refershes itself automatically. Hard paints have a better, smoother finish, but are harder to refinish.

[rharris8]

This boat has been painted several times with some very deep chips, so I thought it best to strip before repainting. I did some trial chemical stripping of the hull and deck areas yesterday, and thought I should get some advise before proceeding. Directly over the fibreglass cloth there is a black resinous layer (the entire boat) which is more prone to softening that the subsequent layers over it. On the hull, there is a vey tough (to strip) cream colored layer directly over the black stuff, topside there is a blue material which is not as tenacious. There are other layers on top of these but I'm guessing that these were probably original when the boat was manufactured.
What is this (relatively thick but softer) black layer?
What might these other coatings be?
Should I quit using chemical stripper since it is hard to control the reaction and start sanding?
What materials should be used over areas that now show the fibreglass cloth, Epoxy primer?
Should I not worry about starting to expose the cloth and continue chemically stripping?

[marshmat]

It's called "gelcoat". It's a special type of resin that's sprayed into the mold to form the outer, waterproof layer of the hull, before the fibreglass is laid up.

Don't strip the gelcoat off. You can sand and paint over it. If it is blistered or breached anywhere you need something like Interprotect or Hysol to make it waterproof again. If you strip it, water will get into the laminate and crack it. Stripping paint overtop of it is usually not necessary if they are solid layers. Chemical strippers generally don't get along too well with fibreglass.

The normal way to prepare a hull for paint is:
- Pressure wash and scrub it clean
- Sand, patch, sand, patch, sand, sand, sand
- Wash with acetone or dewaxing solvent
- Prime, sand, prime
- Paint

If you have a place nearby that sells marine paints, pick up Interlux's little blue brochure (free), it has most of what you need to know in it.

[rharris8]

Thanks Matt - Between what you've mentioned and what I found @ jamestowndistributors.com, I've got a good start on what to do.
Basically, I'm going to sand down to where the gelcoat starts to become visible (Boy am I glad it's a small boat!). I think it's a good idea to take off as much paint as possible since there are some good sized chips (3 layers thick), that expose gelcoat. This will (at least) get me to an even surface for subsequent painting. I'm still uncertain as to the necessity of priming (I am using Interlux Bottomkote ACT - some documents advise 10 mils of Interprotect 2000, some don't)?!? I'll be sanding off 30 mils and reapplying 15?