polyester resin questions

Discussion in 'Fiberglass and Composite Boat Building' started by hospadar, Jan 27, 2014.

  1. hospadar
    Joined: Apr 2011
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    hospadar Junior Member

    I'm going to be using polyester resin on my next boat project and I've only ever used epoxy for glassing before so I have a couple questions. Mostly I want to try polyester because I'm just building a dinky little rowboat (a pd-racer/bolger brick kinda thing) and I don't want to blow the cash on a ton of epoxy.

    I'm wondering about waxed/unwaxed resins. It seems like it would be easiest to buy unwaxed expoxy and mix in the wax myself for the final coat. I'm just doing one layer of fiberglass over plywood (the corners are going to be chine logged, not stitch-and-glue). Thoughts/opinions?

    I'll probably do some ghetto vacuum bagging with a shop vac and fabric-store peel ply. I've always had problems glassing around sharp corners and I'm hoping that even a somewhat lame vacuum bagging job might help with that. I've heard polyester/dacron and ripstop nylon both will work as peel ply, does anyone have experience with these with polyester?

    What's the best way to fair the hull when using polyester? Can I use unwaxed resin with some filler (will the tackiness make it un-sandable)?
    I could fair with epoxy but I'd rather avoid having to buy epoxy alltogether

    I was planning on just painting over the resin instead of bothering with gel-coat.
  2. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    You really should use epoxy over plywood. You don't need to buy the big name brands, you can buy online from places like Aeromarine for reasonable money.
  3. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Welcome to the forum

    I'd second using epoxy rather than polyester, for glass over ply. Much more reliable. One coat at least on bare wood, possibly two (depends on sinkage) then glass coat follwed by rub down and one or two more coats. If you need to fair, then a microballoon/colloidal silica/microfibre or whatever blend you require would be best just after the glass. That gives a coat or two of pure sealing prior to paint. Others may prefer to fair prior to glass.

    You may find using a fine say 200gsm roving rather than fully woven cloth helps with the corners. Or you could trim at the edge and feather in a local tape later. Least you can masking tape onto a dry surface to hold it down.

    Polyester is OK, but better for building a complete shell out of a mould. Dinghies like the Mirror et al were stitch and glue with polyester but not sheathed with it. Polyester is a bit too brittle to sheath with and does not sink in the grain quite as well as epoxy.
    The wax/unwaxed stuff (polyester NOT epoxy) is more important with gelcoat application, whether into a mould as part of build (unwaxed) or rollered/brushed on top as a finish (waxed). Basically the wax allows it to cure in air like paint and it if you want to recoat it (surface wax), must be abraded off first.

    It can be put on top of epoxy in the latter scenario, but be aware of potential problems if using a mould as a keying resin/coat is usually required, check out Tycoat - I think that is the one West recommend. I know of a run of at least 10 complete hull/decks that were scrapped because a keying coat was left out in their construction......
  4. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    If you are going to use poly make sure you sand off the surface gloss on the ply first, we used to add a bit of promoter to acetone and brush that on next to help with the "key"
    Finally use peel ply as a substitute for waxed resin, much more betterer.
    Oh, and if it is a pretty thin layer give it a bit of a post cure.
  5. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    Oh, fairing.
    We used a product called plug white, waxed gelcoat with a sandable filler added. Not really kosher for boats but okay for a cheapy !
    Have fun.
  6. messabout
    Joined: Jan 2006
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    messabout Senior Member

    I have used visqueen many times for the peelply function. Cheap, works fine with polyester, weldwood, titebond, or epoxy.

    I join the others in recommending epoxy rather than polyester. The cost difference is small and the long term favorable result is large.
  7. Ilan Voyager
    Joined: May 2004
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    Ilan Voyager Senior Member

    I'm going to join the choir of the epoxy singers. Any cheap epox resin will work better that the classiest isophtalic polyester.
    But I'm going to add my own song:
    Just for making a dinky row boat the difference of price will be nil, maybe even more expensive with polyester. How? simply you will have to to buy promoter (cobalt naphtenate, pretty toxic stuff), plus lots of acetone or a solvent (fire hazard), plus styrene (rather toxic and the best headaches of the world) to dilute the resin of the first coat, you will need paraffin also for waxing the resin. Plus the common stuff common to any work with a resin (brushes, fillers, etc...) but that it's a constant in the calculations of cost. With epoxy, you'll only need an epoxy kit, plastic squeeges and cheap throw away brushes. The use of solvent is minimal.
    You will need a better paint as polyester is "porous" even out of water so you have to seal it in the absence of gelcoat (which is rather expensive and heavy for small boats).
    For an epoxy boat, a cheap automotive acrylic paint will do the thing for long years.

    If you're have neighbors, be sure that with polyester you'll have complaints. That stuff smells hard and produces tons of stinking vapors while curing. If you're married your wife will hate you if you're making the boat in the basement or in the garage. Be sure to spend a good time of chastity as the repulsive smell of styrene impregnates every thing, and your skin first. Worst, your dog and/or your cat won't even approach you. The food you eat will smell styrene. The Budweiser will smell styrene.

    That was the complaint of the lonely life of the poor polyester worker.
  8. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    So you don't like polyester much then ? :D
  9. Ilan Voyager
    Joined: May 2004
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    Ilan Voyager Senior Member

    It's a good material for making long lasting boats. It has made it's proof. No problem in a shop with no close neighbors and a lot of aeration. Plus the due security precautions: polyester burns dangerously well, it needs lots of flammable solvents, promoters and catalysts are very dangerous stuff, which explodes if they are accidentally in contact. Catalyst is a peroxide and one drop in a eye can make big problems. We had always plenty of eye cleaning-rinsing solution and the special applicator in the shipyards, as simple water is not enough for a peroxide accident.
    It's a product for industrial plants or if you have a remote shop far from your house (and the others) with plenty, I mean plenty of aeration with maybe extractors. Styrene is not an inoffensive product and it makes a lot of vapors.
    Also insurances are pretty expensive when you have a shop working polyester.

    Good stuff for making boats, but has nothing to do first for working on wood and less on wooden boats, second in a house or in a garage close to a house, third think about the neighbors, and the difficult relations you'll have with them...And think about the fire hazard.

    About the personal effects of the smell, I was only half joking. Make the experience of working polyester during 2 days and after try to taste a good wine (a Beaumes de Venise 1996 for example) or to be gentle with your sexual partner...
  10. Westfield 11
    Joined: Apr 2008
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    Westfield 11 Senior Member

    Polyester makes good fiberglass boats, it does not make good glass over wood boats. It bonds well with polyester or fiberglass, but not so good to wood, requires lots of chemicals to promote wood bonds. Why not use epoxy and avoid all the mess and problems AND end up with a boat that will last for decades as opposed to years at best?

  11. leaky
    Joined: Sep 2008
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    leaky Senior Member

    Hey, just wondering from my amateurs standpoint - with something small like this - why do you even need the plywood?

    I would just build a mold out of hardboard, coat with a release agent, gel coat, then lay glass in there.

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