epoxy vs polyester resin

Discussion in 'Boatbuilding' started by mkpardy, Jan 19, 2007.

  1. mkpardy
    Joined: Jan 2007
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: nova scotia

    mkpardy Junior Member

    i'm a new member and would greatly appreciate any input.
    i'm looking at building the console skiff and polyester resin and cloths are
    easily attained becuase there is a boat building shop about 2 minutes from my house.i have fiberglassed a couple of boats in the past but never a stitch
    and glue. the polyester seem to have worked ok but i'm wondering about
    strength,delamination and the number of layers i may need to apply.
    i live in nova scotia and we sometimes get a decent chop in the water
    3'to 5'. any input:?:

    thanks kevin
  2. RatliffFranklin

    RatliffFranklin Previous Member

    Boats are so overbuilt compared to airplanes or racecars I'm not sure if the comparative strength of epoxy versus polyester really matters.
  3. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    The strength doesn't matter quite so much as the adhesion and waterproofness (is that a word?). Polyester doesn't adhere to plywood as well as epoxy, nor is it as waterproof. Polyester is also more brittle and may crack with the flexing of the hull panels, whereas epoxy will flex with the panels while staying stuck to the wood (keeping it sealed). Any EXTERIOR application of resin should be of epoxy. Fillets and taping should also be of epoxy. You might get away with coating the interior panels with poly. Epoxy will glue Poly but poly will NOT stick to epoxy with any strength so bear this in mind...fillet areas should be left at bare wood for the best adhesion of the epoxy. The number of layers (of glass I presume) are largely dependant on the purpose of the glass...if it is structural, then a layer of roving, a layer of matt then a layer of cloth would probably do...depending on how thick the plywood and how big the boat. If the FG is simply for abrasion resistance then one or two layers of cloth should be sufficient...again depending on the size of the boat and how many rocks you intend on denting.

    So...What are you building?

  4. mkpardy
    Joined: Jan 2007
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: nova scotia

    mkpardy Junior Member

    polyester resin

    thanks for input. i'm thinking of the glen l console skiff 15'6".
    what if i used 24oz roven as a layer along with a few layers of
    mat on the exterior and 2 or 3 layers of mat on the interior .also did i mention that poly resin is $28 gallon and epoxy is
    about $135 gallon. what do you think.and again thanks for the input
    its greatly apprecieted
  5. RatliffFranklin

    RatliffFranklin Previous Member


    I don't know what taxes and import regulations are like in Nova Scotia, but have you looked into the possibility of getting your epoxy resin by mail order?

  6. SamSam
    Joined: Feb 2005
    Posts: 3,817
    Likes: 153, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    Do what the plans tell you to do. With 5 layers of mat and 1 of 24 oz wr, that's what some pure fiberglass boats are made of, without the wood. The plans call for 1 layer of 7 or 8 oz cloth on the outside only. That's 7-8 oz per square yard. Your 5 mat plus 1 wr equals 91.5 oz per square yard. And that's just the cloth, not the resin also. Sam
  7. lewisboats
    Joined: Oct 2002
    Posts: 2,329
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member


    Are you building an GRP design or Stitch and Glue? What do the plans say and what is the boat? With a layup like that you don't need the wood but you will need a mold...and a crane.

  8. LP
    Joined: Jul 2005
    Posts: 1,403
    Likes: 56, Points: 58, Legacy Rep: 584
    Location: 26 36.9 N, 82 07.3 W

    LP Flying Boatman

    I couple of other places to look for epoxy.

    I've heard good things about the 350 resin. Good for clear coats. My current product. Tends to "go off" slowly.

    Tends to blush, but has a good working life and "goes off" quickly.

    Less expensive than West System and some others.
  9. tom28571
    Joined: Dec 2001
    Posts: 2,469
    Likes: 113, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    The epoxy/polyester subject has been covered ad nauseum. There is a clear result and it is epoxy for a wooden boat. No point in restating all the many reasons here and this is a no-brainer.
  10. mmd
    Joined: Mar 2002
    Posts: 378
    Likes: 16, Points: 0, Legacy Rep: 309
    Location: Bridgewater NS Canada

    mmd Senior Member

    If a plywood stitch-and-glue construction project, it is as tom28571 says - a no-brainer. Polyester does not adhere well to wood and will allow moisture penetration, both disasterous to the longevity of your boat. Check out the comparitive costs of System 3, East, West, and MAS epoxies - I think that you will find East System is probably the best price locally. Don't go overboard with extra laminations of cloth; unless you re-engineer the structure to determine a lighter ply you are merely adding weight and cost.
  11. ted655
    Joined: May 2003
    Posts: 640
    Likes: 14, Points: 0, Legacy Rep: 122
    Location: Butte La Rose, LA.

    ted655 Senior Member

    "Stich & glue" boat plans came on the homebuilt scene AFTER epoxy started being used. Hmmmmm?
    Not just strength, water resistance, but..... forgivness. Make a mistake with epoxy and it still gives good results. With polyester you have to be spot on. It's a pros material.

  12. mkpardy
    Joined: Jan 2007
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: nova scotia

    mkpardy Junior Member

    epoxy it is

    thanks for all the input guys, i really appreciate it.
    I will be using epoxy (east) for my project boat.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.