View Full Version : Recoating the bottom gell coat ?

10-25-2012, 12:08 PM
I became aware that some 10 year old glass boats develope blisters on the bottom in fresh water. Put the fear in me to protect my 2002 Chaparral 186 SSI before blisters appear. Can I simply prep & re-gell coat the wet area that is submerged 4 months a year ? St. Lawrence River.
Will that give me another 10 years again ?..............At 75. I would be happy with 5 more years. :d


Bob Adams
10-25-2012, 12:26 PM
At 4 months per year, I doubt if you are going to blister. If you are woried, use something like Inter Protect barrier coat overcoated with a hard antifoul.

Todd Bradshaw
10-25-2012, 10:09 PM
Gel-coat application isn't something that's very easy for amateurs to mess with for anything other than small spot repairs. You pretty much have to spray it and it will usually go on with a substantial amount of orange-peel. To get it back to a smooth surface, you then have to sand it heavily and then go through the steps needed to buff it back up. In addition, it is air-inhibited and will only cure hard on the surface with a surfacing agent added or a layer of plastic over it to seal it off from the air. It's just not something you want to mess with.

The epoxy compounds (either a pre-mixed, like the Interlux or home mixed, like WEST Epoxy and their aluminum flake barrier coat powder) are the way to go, but still a substantial amount of work. It will probably take as many as five or six coats, rolled on, to give you the required 10 mils or so that are needed for decent protection. Then, assuming you want a smooth finish, this would need to be sanded smooth and finally overcoated with bottom paint.

Whether or not a boat will blister is kind of a crap-shoot and very hard to predict, but I think most folks would wait until they see they have a problem before diving into such a project. In cases where there is a serious blistering going on, the fix generally starts with grinding off most or all of the gel-coat before re-coating with the epoxy mix, so it's a big job.

M. J. Notigan
10-25-2012, 11:27 PM
Having just rolled on 5 coats of Interprotect 2000e on the hull of my Mictrotrawler build in the past 5 days (wood-epoxy construction.........I am primarily using the Interprotect as a primer), I can attest to what Todd just stated as gospel. The Interprotect likes to be rolled but tipping with a brush was too much work for my 1 man operation. It cures with an orange peel finish that will require sanding to smooth it out for your topcoat of antifouling. It was easy enough to mix and ready. You would want to add the Interlux 2333 reducer to thin it out somewhat.

From what I understand, it's not so much the fresh water that causes fiberglass blisters, rather, it's any water migrating past the gel coat into the fiberglass resin and cloth, where the water reacts with any uncured resin, creating the blister. Modern day fiberglass boat construction often consists of vinyl ester resins which resist this blistering much better then the older fiberglass polyester resin formulas. It may be worthwhile to contact Chapparal to see if your boat was constructed using vinyl ester or poly ester. My opinion? Inspect and repair any cracks in the underwater body, apply the interprotect as per Interlux instructions followed by a hard anti fouling such as what Bob Adams here suggested. Good luck!

Take Care.

wizbang 13
10-26-2012, 06:27 AM
I don't think that the hardness of the anti fouling has anything to do with it.

10-26-2012, 10:16 AM
Thank you all.
I am going to check the bottom every in & out each year. Will repair when the problem starts.