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Old 08-03-2009, 08:11   #1
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Fiberglass Expert Needed

A customer of mine has asked me to remove vinyl covering walls of the shower stall in his trawler, with the idea of gelcoating the enclosure. I now have the vinyl removed as well as all the old contact cement. Two of the walls are appear to be high quality marine plywod, the third wall is actually the inside of the hull, (Polyester resin). I am trying to avoid laminating cloth over the plywood areas for a number of reasons. My question is do you think it will be suitable to just coat the plywood with fresh polyester resin and then spray the gelcoat or should a laminate of cloth be applied as well to insure stability of the substrate. The plywood is tabbed to the hull and there are areas where there is just poly with no cloth and there are no cracks.
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Old 08-03-2009, 08:42   #2
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A customer of mine has asked me to remove vinyl covering walls of the shower stall in his trawler, with the idea of gelcoating the enclosure. I now have the vinyl removed as well as all the old contact cement. Two of the walls are appear to be high quality marine plywod, the third wall is actually the inside of the hull, (Polyester resin). I am trying to avoid laminating cloth over the plywood areas for a number of reasons. My question is do you think it will be suitable to just coat the plywood with fresh polyester resin and then spray the gelcoat or should a laminate of cloth be applied as well to insure stability of the substrate. The plywood is tabbed to the hull and there are areas where there is just poly with no cloth and there are no cracks.
I would be adding a fibreglass or even plastic false wall, as the shower stall, attached to the side of the boat. Be easier to achieve a good finish as well. and easier to seal the corners.
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Old 08-03-2009, 09:02   #3
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This reply doesn't address the question.
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Old 08-03-2009, 09:35   #4
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My repair would be all Epoxy with cloth followed by two part poly. I would worry about the different expansion rates with gelcoat over basically plywood. This reply addresses the question...
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Old 08-03-2009, 09:58   #5
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Coat the plywood and hull sides with several coats of epoxy, finishing with a high solids epoxy to increase the water barrier properties. Then spray the gelcoat. Ensure of course that you remove all amine blush after the epoxy cures. West Systems has an article on applying gelcoat to epoxy that is worth the read.
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Old 08-03-2009, 10:13   #6
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My repair would be all Epoxy with cloth followed by two part poly. I would worry about the different expansion rates with gelcoat over basically plywood. This reply addresses the question...
Ditto. Should that plywood get wet. Any wet/dry cycles will crack the resin and gelcoat, eventually falling apart.
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Old 08-03-2009, 10:13   #7
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Glass or No Glass ???

If your customer is going to keep the boat versus fix it up to resell, then I would opt to add the glass fabric. Overlap the plywood and hull joint area to keep all water in the shower area. I think this would be more appealing to the owner. A few coats of resin over the plywood with glass fabric overlapping just the plywood and hull joints is a good second choice. I would hesitate to just gelcoat over the plywood. I do not have much faith in the lifetime of that solution. -- Chesapeake
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Old 08-03-2009, 10:13   #8
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definately cloth...finish cloth ok. polyester ok. Thin first coat with styrene to penetrate plywood. Dewax hull with acetone, fully scuff sand, rewipe thouroughly with acetone, don't forget the wax in gelcoat (or prewaxed) or it won't kick. Not intended to be full course in fibergass. Wear cartridge mask
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Old 08-03-2009, 10:23   #9
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Capt Cook, kinda what I was leaning towards. FYI for the rest of group epoxy and gelcoat are not compatable with each other
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Old 08-03-2009, 10:35   #10
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FYI, they are: EPOXYWORKS Just have to know what you are doing...
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Old 08-03-2009, 10:42   #11
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FYI for the rest of group epoxy and gelcoat are not compatable with each other
Of course they are. Gelcoat adheres to epoxy just as well as it adheres to polyester.
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Old 08-03-2009, 11:18   #12
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Hi all, just some points to consider:

- cloth or no cloth: strength and impact resistance is the issue, not waterproofing. Epoxy-coated plywood with gelcoat finishing is quite vulnerable when impacted with stuff like shower-head, tools etc. A single layer of 125 grams cloth takes care of that. If the connection of the bulkhead with the hull isn't cracked anywhere, it's proven strong enough so cloth isn't needed for strength here. It's just surface-finishing of the head for a proven sound construction.

- putting cloth on a vertical surface is more work than on a horizontal one in regard with filling up the weave with resin. Many use a little filler to make it easier but use of the spreader is mostly replaced by the roller. I always use the dry layup method on horizontal surfaces but wouldn't try that on vertical

- Gelcoat adheres well to polyester, vinylester and epoxy, but the gelcoat itself is polyester. When you put it on vinylester or epoxy, it will have a different expansion-coefficient with heat/cold and cracks are more likely compared to application on polyester (tell me about it, Sundeers have these cracks everywhere).

- Consider awlgrip instead of gelcoat for reason above. Or consider use of polyester instead of epoxy. My pref would be epoxy + awlgrip but it is the more expensive one.

- penetrating plywood: according to the Goucheon brothers (West System) thinning the first coat of epoxy isn't needed/recommended. Heat up the plywood with heatgun just before rolling standard resin-hardener mixture on. The air in the plywood will contract during cooling, sucking the epoxy into the fibers in the process.

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Old 08-03-2009, 11:46   #13
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"I am trying to avoid laminating cloth over the plywood areas for a number of reasons. My question is do you think it will be suitable to just coat the plywood with fresh polyester resin and then spray the gelcoat or should a laminate of cloth be applied as well to insure stability of the substrate".

What are your reasons??? Polyester resin isn't that great for plywood. The wood creeps too much over time with temperature and especially moisture. For the size of the job, I would acetone the walls well, hot coat with epoxy, then use a medium weight cloth wetted out and squeegeed well. Give it a weak to really cure, then spray or brush poly-urethane. The only disadvantage I can see are the fumes.
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Old 08-03-2009, 12:18   #14
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It makes sense to me to glass the ply first, and that is how I've done all my interior work.

BUT, having said that, during the rebuild on my 31 year old boat I have found many, many interior surfaces that seem to be gel coat directly over ply wood.

These include the original showers and amazingly there was no checking or cracking to speak of…or any impact damage??
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Old 08-03-2009, 12:48   #15
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I did a simlar project when I converted the v-birth to a head in one sailboat. After first filling any gouges or depressions with epoxy resin and filler, I covered all plywood with epoxy resin and woven glass matt. I also rounded out all joints with epoxy and filler. The result was an even surface that was very unlikely to crack with flexing and expose the ply underneath and had a nice seamless finish all the way around. It held up very well. A friend of mine has applied polyester resin directly to plywood and been dissapointed with the results. His experince was similar to mine and that is that polyester resin just doesn't bond to plywood that well, is prone to cracking, doesn't leave as smooth a finish and joints will not hold up well.
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