Removing bottom paint/barrier coat with a heat source

[kirstindally]

Hi there,

I have a blister issue and first need to remove the old antifouling (10-12 coats!) barrier coat, and gel coat from the boat. It was suggested to me by a friend that I use a heat gun or propane torch to soften and scrape the old layers off, which is what he did on his wodden hulled boat with great success. I did a small test patch and it seemed to work ok. However, I have had difficulty finding any information on the web about doing this to a fibreglass hull (70's era and presumably polyester resin). I was hoping someone may be able to shed some light on the viability of this and whether there will be any adverse effects on the hull.

I look forward to your replies and going sailing again soon!

[Fstbttms]

Sounds like a really bad idea to me.

[Maine Sail]

I would not advise heat, especially flame, to remove paint on fiberglass. With wood it's one thing, if you are skilled at it, but fiberglass does funny things when you apply to much heat.

I would suggest finding a yard with a peeler as stripping the gelcoat is some serious work. If the bottom paint was a hard paint it won't soften well with a heat gun anyway. The best method I have used, and seen used, is lots of razor blades and a scraper handle for the blades. This will get about 85% of the paint off the rest you'll need to get with a vacuum sander. The gelcoat is another story you can sand it off or use a peeler and this is a TON of work!

You'll also need to ascertain the hull is dry before applying a barrier coat. It can take months for a hull to dry properly even with the gelcoat removed. A moisture content of 3% on a solid GRP hull is considered saturated...

[sailingdog]

If you have to remove that much, I would highly recommend hiring someone with a gelcoat planer/peeler.... it will be much more efficient, faster, and safer than using a torch or heat gun.

[CalebD]

Ditto what has already been said about open flames on hull paint and fiberglass. The folks who have posted already have owned keel and other boats with training hulls longer then I have had a keel boat (SD has a trimaran and has an encyclopedic knowledge of all things related to boats - no BS).
Without knowing how big the boat is (is it a Tartan 37' or a Tiburon or what) and where it is located (Mexico? - I checked some of your other posts) and since you say you have some 'blister' issues on the hull I will tell you what little I think I do know.
The best (and one of the messiest and fastest) ways of removing hull paint, gel coat and fairing out any blisters will be with a tool called an 'angle grinder' or just a grinder. There are versions in 4 1/2" and 5" on up. Here is a link for a Makita 4-1/2" angle grinder: Amazon.com: Makita 9557PB 4-1/2-inch Angle Grinder w/Paddle Switch, (AC/DC): Your Store
which is a better model then the el-cheapo Black&Decker model I have.
You can buy semi-flexible sanding disks that you can attach to the grinder that come in varying grit sizes (#30, #60 etc) that I can't seem to find on any of the 'friendly' box store websites - grrh$#!+). I get them in a lumber store or hardware store for a buck or two a piece. Do not use a solid disk for this as it will do more harm then good. The flexible sanding disks (what I am calling them but no one else seems to) are good because they take off a significant amount of material quickly and are pretty easy to control if you keep them moving (unlike a belt sander which will quickly make a mess and make your hull un-fair (not smooth). The final sanding would need to be done with a normal flat Random Orbital sander to take out any of the 'proud' spots left over in the 'massive removal' stage. You were planning on putting a new barrier coat on anyway weren't you?
The problem with this kind of procedure is that it will make a hell of a lot of dust which many yards will not allow and the person doing the work needs to have a respirator, full suit and goggles etc (yes, even Mexicans should wear protective clothing for this kind of work if your work is being done in Mexico, which should cost a lot less).
Most will tell you just to use a heavy grit paper (#40 or #60) with a normal Random Orbital sander attached to a vacuum because you will not be able to mess up the shape of the hull too fast with a tool like that and I would agree. There is a certain amount of finesse one can gain though by working with these 'sanding disks' (that I can't find a ******* link for) with the angle grinder and the amount of pressure used that would take off the material much faster (and messy-er because the angle grinder has no vacuum attachment) but pretty evenly none the less.
Since I think that you have a 37' sailboat I am going to guess that you will probably not be doing the work yourself. Using the right tool or contractor for the job can make a messy, unforgiving job go faster.
Good luck.

[kirstindally]

Thanks for the feedback. The boat is in Mexico right now, Guaymas, and I can't imagine the yard would have a planer. Any suggestions as to where I might buy one, or are they expensive?
Cheers

[kirstindally]

Thanks Caleb D. The boat is 36' and I plan on doing it myslef for sure. I have already started with the method you described, and it is exactly as you described. I have a mask etc... I am back in north america right now and will return soon, ready to do what it takes. I guess heat is out, so I either find a peeler/planer or get down and dirty with the grinder and sander. I appreciate your feedback.

[sailingdog]

Don't know the cost of the unit, but one of the handheld gelcoat planers is available here.

[camaraderie]

If you can't get a peeler...you can do it the old, hard way by using a circular saw blade with adjustable depth to cut through the paint and gel coat in close parallel lines...then chisel out the sections. Just be sure the depth does not get into the laminate..only the gel and mat.

[kirstindally]

Thanks, very useful info. Hadn't thought of the circular saw method, but in theory it could work. Cheers