Patching and Painting a Fiberglass Sailboat?

August 7, 2009 12:48 PM

I accidentally bought an old 12' sailboat this morning. How do I repair and paint the fiberglass?

So I was out garage sailing, minding my own business, and came home with a 12' sailboat. It is a Sunfish (I think) from the 1960s and is in pretty good shape. The pictures linked above show the fiberglass patches it has already, and also a gash along the keel that needs to be patched.

I want to patch and paint it. Any advice? My idea is to get a fiberglas patch kit from the auto parts store and patch the keel, to sand the whole underside down, and to prime and paint it. What kind of primer and paint do I use? Can I get away with foam rollers for putting on the paint or do I need to borrow the neighbors compressor and spray gun?

I am not looking for any kind of show quality at all here, just a functioning boat we can play around with on area lakes. Thanks!

posted by LarryC to sports, hobbies, & recreation (14 comments total)

I would check out an auto paint and body supply. They'll have significantly better deals on mat and resin.

If it were me, I'd start building up from the inside of the hull, but keep as flush to the current surface as possible. Once you build up some strength on the bask side, put thin layers of mat on the outside to "fill in" where you need. Sand it down flush, let it cure, and see if you have any pinholes left to fill with resin. Once that is done, then give it a final sand and gelcoat it versus paint. Look up a product called Duratec. You'll want to spray it on.
posted by chrisfromthelc at 12:55 PM on August 7

Book?
posted by electroboy at 1:13 PM on August 7

I'd recommend getting a decent book for this actually.
First of all, there are two layers to a fiberglass boat, the fibre glass itself and then the gel-coat which protects it from water.

If you intend to leave it in the water when you're not using, then you need to coat the parts of the boat below the water line with anti-fouling coating to prevent barnacle growth.
posted by atrazine at 1:25 PM on August 7 [1 favorite has favorites]

What everyone else said about getting a book (even if you just borrow it from the library) -- there are a bunch of finicky details involved like the different types of matting and resins and what will stick to what else and what will crack off in the middle of the lake the first time you run aground. Another good resource to check out might be forums for people who restore cars with fiberglass bodies, like a Lotus Elise.

Good luck!
posted by SpecialK at 1:33 PM on August 7

Also: I might suggest sanding off more of the gelcoat or paint to see if you can find more patch areas that might've been improperly done.

Most of the people who seem to do this seriously don't use a palm sander, they use the longest piece of sandpaper they can possibly wrap around a wood block to avoid having valleys or a orbital sander with a variable speed control.

Also, most people who do this as a hobby don't use a sprayer to do gelcoat, they use a roller or brush-on varient. Spraying on gel coat can create ripples because it's not self-leveling like paint is.
posted by SpecialK at 1:38 PM on August 7

Here's a thread with some good product names in it: Applying Gel Coat.
posted by SpecialK at 1:41 PM on August 7

Thanks. I don't think I can get to the inside of the hull though. (Goes to look.) Nope--the deck/cockpit does not allow access.
posted by LarryC at 1:50 PM on August 7

Wow. That's my kind of accident.

For repair, you're much better off using epoxy and glass cloth rather than polyester (i.e., what's typically sold as 'fiberglass') resin and mat. Epoxy has much greater adhesive strength and is also more impervious to water.

You're unlikely to find epoxy resin in the quantities you need locally, so mail-order is you best bet. Duckworks boat building supply caters to home builders and repairers of boats, and they have great prices. It's also a very knowledgeable small business, and the owners (Chuck and Sandra) provide great service and have first-hand knowledge of everything they sell.

You might also want to browse Duckworks Magazine for articles on similar repairs--there ought to be a few. Basically, you'll want to sand down the area, cut glass cloth to fit, paint some epoxy around the hole, apply the cloth, then add more epoxy to fill the cloth. Sand and repeat as necessary. I'm not sure what weight cloth you'd need, but I'm sure Chuck could advise. From this side of the internet, it doesn't look like a difficult repair. Duckworks also has a yahoo mailing list that would be a better source of fiberglass boat repair than a list for fiberglass auto repair.

Finally, as far as paint goes, many folks (including me) have had great results with exterior 100% acrylic latex paint. I used a Benjamin Moore industrial latex paint called DTM (direct to metal) on the hull of a sailboat I built 5 years ago, and it's still holding up nicely (even after a trip to the beach where it was dragged on and off the beach with a few PVC pipe rollers). Others have reported good success with porch & floor enamel.
posted by fogovonslack at 2:48 PM on August 7 [4 favorites has favorites]

I had almost the same accident fifteen years ago. I repaired our boat using stuff from West Marine. I got advice from them on what to use and how to do it, so it might have been less expensive to go to the auto parts store, but we had three years of great fun (before we moved and couldn't take the boat.)
posted by anadem at 3:32 PM on August 7

You don't want to paint it...that's going to add a lot of weight to the hull. Which is not good.

You need to grind away the parts that are bad, fill them with layers of mat that's soaked in epoxy (west system is generally available anywhere). You'll need something to grind with, usually a wheel with 36 grit sand paper on it in a hand held buffer grinder.

It's really unpleasant work. I'd honestly take it to a boatyard or body shop and see what they'd charge you. If you could get out for $100 or so, you'd save having to buy a lot of stuff, and save yourself some nasty work. It's really no fun...I've done a lot of it.

Seriously, put a little paint on the bad parts, but don't paint the whole boat.

Sunfish are still in production, it should be pretty easy to get replacement parts for this boat.
posted by sully75 at 7:52 PM on August 7

I'd go to a boatshop and check out the products available, ask for advice. Do the work outdoors, as it's quite toxic.
posted by theora55 at 10:46 AM on August 8

I don't know that paint would add a significant amount of weight. With a boat that size, you're looking at probably half a quart of paint for 2 coats. Also, fiberglass cloth, with long woven fibers, is much stronger than mat, with short randomly compressed fibers. If you want to save weight, use cloth rather than mat. You'll also need less epoxy to fill the cloth, cutting your expenses. Finally, most fiberglass mat is designed to work with polyester resin--the matrix that holds the fibers together dissolves in the polyester, allowing the mat to fully absorb the resin. If you use epoxy, the matrix may not dissolve, so you won't get full saturation, so there may be strength issues.
posted by fogovonslack at 12:15 PM on August 8

fogovonslack: you are right on one thing...I confused mat and cloth. It's been a while.

Paint will definitely add weight. Not a ton but enough, particularly in a boat you have to lift to move.

You definitely want to use epoxy here. First it's much easier to use, second it bonds better to old surfaces, third, it's much stronger. The boat was made with polyester resin, but generally fiberglass repairs are done with epoxy. As long as you get cloth that's made for epoxy resin you'll be fine. You just need to make sure that you wet it out thoroughly.
posted by sully75 at 4:48 AM on August 10

Sully75--sounds like we're mostly in agreement, then.
posted by fogovonslack at 5:49 AM on August 10