using epoxy and poly resin to do repair

Discussion in 'Fiberglass and Composite Boat Building' started by 61sg, Aug 11, 2009.

  1. 61sg
    Joined: Aug 2009
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    61sg Junior Member

    Hi

    I am doing the old stringer replacement and have read all the epoxy vs polyester debates.

    However i already have bought the polyester resin and most of the work will glass on glass plus i want to be able to flow coat it.

    but for bedding the wood stringers down i am a bit worried about using poly resin so thought i might be able to glue them down with epoxy resin and wipe any excess away as the poly wont stick to a epoxy fillet.
    then fillet and glass tab in with poly.

    not so worried if the tabbing glass over the stringers de laminates a bit from the wood as it will still be held down to the hull mostly concerned about the stringer to hull bond.
    oh its a 18ft ski boat v8.

    any help appreciated
     
  2. glassman66
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    glassman66 New Member

    what works for me is to cut out stringer to fit. then rap them with poly out the boat with 1 layer just to seal all the wood. mask with 2" tape along bottom of stringer and hull along stringer. set in place and glue with epoxy . scoop extra epoxy off with spoon let dry. pull off tape and u ready to glass. dont use cheap tape the glue will stay use 3m hope that helps
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Well 61sg, you're about to learn why we don't recommend polyester for these types of repairs, but since you're determined.

    Don't use epoxy to bond the stringers, it's not as important as the tabbing and saturation. Use polyester, but soak the crap out of the wood, with several coats, then bed the stringers in mat and resin. Follow with substantial tabbing well back into the hull shell.

    Nope, the bond will not be as good as epoxy. Nope the wood will not be really waterproofed, but damn, you save a couple of bucks right. In the end you'll find what we've all found, that polyester for this level of repair, isn't really saving you much and it's more difficult to work with then epoxy too.
     
  4. 61sg
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    61sg Junior Member

    Hmm ok
    Well if i use just epoxy for the whole repair how much resin will i require?

    replacing 2 stringers and coating and glassing down marine ply floor
    4m x 35mm stringer
    3m x 35mm stringer
    two 2400 x 500mm ply sections
    one 2400 x 1000mm ply section

    two layer on everthing im thinking. I know you catn say exactly but a ballpark would help?
     
  5. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    The amount of resin you will use depends on the type of fiberglass you use.

    When I replaced the two engine stringers in my boat I used 1708 biaxle stitchmat. This stuff requires a considerable amount of resin to wet out. On the other hand sealing marine plywood and putting down a layer of say 6oz. cloth will use relatively little.

    I'd order up a gallon or so and see how the project is going, you can always order more. Those stringers are not that big.

    Remember that you'll want to practice using the epoxy and glass. This is not waste, rather it's an investment in doing your project well. You can read as much as you can but there is no shortcut to actually using epoxy, think of it as doing paper mache with toxic materials, you have to actually work with the stuff to really understand it's characteristics.

    best of luck,

    MIA
     
  6. PAR
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    PAR Yacht Designer/Builder

    Part of MIA's issues was the use of a combo fabric (1708) which uses a lot more resin., because of the mat content. Epoxy doesn't need, nor is it desirable to use mat, it just wastes resin. Use regular cloth and or biax.

    The amount of resin you'll need depends on many factors, like MIA (I'm not picking on you, honest) mentioned. The thickness of fillets and back filling under the stringers, etc. will vary from project to project. Fabric requires about as much resin as the fabric weighs to wetout. Coating surfaces is about 100 sq. ft of surface area for three good coats of resin. These are very rough guides.
     
  7. missinginaction
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    missinginaction Senior Member

    I know you're not pickin on me PAR.....I wish I'd known that when I ordered the cloth, I just went with what my supplier recommended. Probably could have saved $100.00 on epoxy though!

    I could have used your skill over the past few days though.

    I've been designing / mocking up the windshield. I knew this would be a bit complicated going in as the old parts were so far gone as to be of little help. In other words I couldn't just reverse engineer it, I had to start from square one. I'll just say that I'm gaining more respect for boat designers and builders all the time. I had to pull out an old trigonometry text and sit at the kitchen table for awhile. It's not easy to get a windshield with a compound angle to mate to a foredeck that has a radius built into it. After I rigged up a jig I test cut some parts and they look good. This took a while and a number of "bad words" came out of dad's mouth according to my son.

    BTW, I'm able to make pretty accurate bevel cuts on the radius with a good jig saw. I thinking that a bandsaw would be a better way cut these bevels?

    I've decided to build the whole windshield out of pine and then cut the "real" parts out of mahagony. Cheap insurance...

    My brain is tired, but it's satisfying to have figured it out. Now I just have to make it.

    MIA
     
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  8. PAR
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    PAR Yacht Designer/Builder

    Compound miters are always fun to work out, though a bevel gauge and some template making is usually the ticket. I usually focus on the one side, in 2 dimensions first, getting it right, then add the extra dimension which is usually just an angle to the mix.

    Now you can ask mommy to spank daddy for saying bad words . . .
     
  9. missinginaction
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    missinginaction Senior Member

    I keep trying to get her to do that but she won't!:D :D :D
     
  10. LMB
    Joined: Nov 2008
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    LMB Junior Member

    O.k., 61sg here's my 2 cents... Use epoxy entirely for the stringers and then use your poly for the deck/sole. Don't under estimate the importance of the tabbing bond when you glass the stringers to the hull (this is where you could run into problems mixing materials). Mixing materials on the stringers can be done but without extreme care on cure and preparations could jeopardize critical bonds. The deck to stringer bond is also important but I think its less likely to make a mistake here. Just make sure the poly/epoxy substrates are completely cured and well prepped before you attempt to bond or glass them to each other in a "mixed material" application.
    I'm in the camp that really good glass work is the most important thing. This only comes with experience so for the novice epoxy is going to be more forgiving. One other tip, look at West systems new caulk tubes of pre-thickened epoxy. That might really simplfy bonding and fileting.
     
  11. 61sg
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    61sg Junior Member

    Thanks for all the advice guys its definatley helping!

    Yeah i thought about using epoxy to tab the whole stringers then switching to poly for the deck but the deck tabs down onto the stringers which would now be epoxy and well it might be ok but it does seem im just causing more problems for myself....

    Im replacing the wet/slightly rotten stringers because i couldnt live with myself if i just glassed them up and done a half job.

    Why cut corners now so i guess epoxy all the way it is!

    just trying to work out a ballpark ive how much i will need.

    will definatley do a bit of practice first, oh and the west caulking tube idea i will definatley try and get some of those sounds very conveinent

    cheers
     
  12. PAR
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    PAR Yacht Designer/Builder

    There's no advantage to mixing the bonding or saturation materials. If you elect to use polyester, then don't bother with the epoxy. Polyester doesn't stick to epoxy, so it's not worth the trouble. If you elect to use epoxy, which does stick to polyester, then you'll use less material, have less difficulty, produce a stronger end result and this can be enough in savings to offset the additional resin costs.

    Rater then spend full retail prices, try this stuff from Bateau.com

    http://boatbuildercentral.com/products.php?cat=41

    It's blush free and considerably less then the major brands. Joel at Boat Builder Central can help you with fabrics and other supplies too.
     
  13. missinginaction
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    missinginaction Senior Member

    In the end you'll be glad that you used epoxy. One thing that I didn't see mentioned is the speed of the hardeners. You probably know that there are generally three speeds, fast, medium and slow. When I first started to work with epoxy I bought the fast hardener. This is OK if you're just bonding a single part, but if you're laying up cloth on a stringer or wetting out a deck, the fast hardeners are, well, too fast. They cure too fast. I've seen people try to work fast before the resin sets up....for me this is not a good idea. Especially when you're doing this as a hobby, you need time to think. I use only medium and sometimes slow hardeners now. Sure, I have to walk away from the job for awhile after application, but I can relax while I'm working, secure in the knowledge that I have some time. Makes the job more enjoyable and much less stressful.

    Hope your boat works out well for you,

    MIA
     
  14. 61sg
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    61sg Junior Member

    I have made templates of engine mount holes and mount height in relation to the hull.

    LH stringer is out, shaping new one and hull is keyed up ready

    The engine mount pedestals are glassed to side of stringers my question now is do i use solid timber or ply for the new pedestals?
    Im worried ply layers would delaminate with bolts going into the edge
    and if i use solid timber the grain will run vertical the same way as the bolts not sure if that is ok?
     

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  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You can use either if you "bond" the fastener holes with epoxy. Drill an over size hole, fill it with thickened epoxy, then screw in the fastener while the epoxy is soft. This will insure the fastener is holding on to epoxy and can't let moisture into the wood. This trick works best with machine threads not wood (the more threads the better). So, for an engine mount, what I do is cast in "studs". If you coat the threads with paste wax (three coats minimum) before inserting it, they'll come out easily when you want to remove them, leaving perfectly cast threads, in the wooden engine bed to accept another bolt or stud.
     
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