bonding plwood toghter

Discussion in 'Fiberglass and Composite Boat Building' started by nomad821, Dec 7, 2010.

  1. nomad821
    Joined: Dec 2010
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    nomad821 New Member

    rebuliding my transom on my 1976 Chrysler have looked up a lot in infomation so for but still wondering how to bond the new plywood toghter and to the the outerskin any help would be great if anyone has done this, thanks
     
  2. War Whoop
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    War Whoop Senior Member


    Do you have room for epoxy in your budget?
     
  3. gonzo
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    gonzo Senior Member

    One layer of 3/4oz mat well soaked in polyester. Prime the plywood first with the resin so it doesn't get dry spots. Use any old screw holes to pull the plywood to the outer skin with screws and fender washers. If you have an outdrive, cut the hole roughly and then use clamps and blocks to pull it tight too. The second layer of 3/4" plywood needs a layer of mat too. It makes for better adhesion. Use 1 1/4' deck screws to get them together and you can leave them in. Epoxy is fine but overkill.
     
  4. War Whoop
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    War Whoop Senior Member

    This would be a old outboard boat,that is why I was worried about the transom loading.
     
  5. nomad821
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    nomad821 New Member

    bonding plywood

    thanks it is a older boat but looks good and the moter a evinrud 88 that runs strong thats why i want to rebulid the transom just need to know how to bond the new plywood toghter to the outer skin and toghter
     
  6. War Whoop
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    War Whoop Senior Member

    You could use Gonzos method or the Epoxy glue, a few waxed through bolts (I use pieces of all thread )to draw it up and make sure you have a strong backs across the transom to keep it straight.

    The main thing is a clean 36 grit ground surface for the bonding on the boat,also do a dry run to check your clamping system out.
     
  7. michael pierzga
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    michael pierzga Senior Member

    As war whoop observed, The clamping system is important...Think about the system and do a trial run, then think about it again.. If its a large surface area, you will need plenty of clamping area to generate 100 percent, surface to suface contact on the glue faces. Allthread thru bolts and angle iron make a good clamp for some surfaces
     
  8. nomad821
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    nomad821 New Member

    do i have to aply a fiber mar between the plywood and the skin and in between each layer of plywood
     
  9. War Whoop
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    War Whoop Senior Member

    Yes use a mat between layers that will help provide a good bondline and knock some 1/8" holes in the plywood to allow air and excess resin to escape as it is drawn up.
     
  10. LMB
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    LMB Junior Member

    All good points but I will add a few insights as well. Obviously getting good bonds is the most important issue. Limited working time for you resin can be a big hurdle and also getting good contact on the irregular surfaces. IMO a single layer of 3/4oz mat will not be enough to get good surface contact for mating up, especially for the core to skin surface where the skin surface is pretty irregular from the grinding prep. If you go that route two layers of 1.5oz mat would be best, but this can take a while to wet out and jeopardize your working time so be careful. I usually glass a layer of mat on all surfaces to be bonded let that set up and then join together with a resin putty that I mix myself. I usually bond the plywood together first and then put in the boat - like others have said, after a dry run. You will need alot of clamping to pull the transom skin up tight and make sure you have a good large flat backing along the engine mount surfaces - so it stays perfectly flat, otherwise the resin/putty can squeeze between your bracing causing hi/lo spots along the engine mounting surface. Also, using mat only applies if you are using polyester or vinylester resin. If you opt to go with epoxy, there are some pre-thickened products available in caulk tubes that would work great for bonding together. Gives more working time and eliminates the mat. Easier, but costs more.
     
  11. stilloutoffocus
    Joined: Apr 2009
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    stilloutoffocus dealership repair flunkie

    im going with LMB on this one, i always use two layers of mat anytime i bond anything together. ill usually layup one on each surface and then put a little extra resin (i use polyester though im thinking of upgrading to vinylester) as the jelly in the sandwitch so to speak, then i clamp/screw the two layers of plywood together (i use drywall screws, several from each side for an even bond) after that cures ill prep the whole transom and do the same method between the new transom wood and the hull surface. i usually use C-clamps for this but ive got some big deep throat multi-clamps (like c-clamps but with multiple screws along a deeper flat jaw line) to help spread the pressure out over the full width of the transom. though i have used 2x4's with several clamps in some cases too. if you go back to the original transom thickness and be sure to have good bonds throughout you shouldnt have to worry about the transom loading mentioned, it is afterall pretty much the way it was built at the factory. after all that is set prep the whole inner transom surface again and lay up at least two layers of matting and one of good roving woven to give it all strength and seal it up well. and you should be good to go!

    p.s. i do reccomend using AT LEAST 36 grit or better when doing prep for polyester as i understand this material relies on a mechanical bond when adhering to any cured surface so the rougher you can make it the better.
     
  12. War Whoop
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    War Whoop Senior Member

    on the back side he can use cabosil with the resin coating (the transom side of the plywood) and a mat layup on the boat transom and make sure there are bleeder holes in the plywood at least in the top half. Try to do a neat job with the grinder and avoid scalloping the thing. Mat comes 3/4 -1-11/2-2 and 3 ounce so pick one suitable, do not use a fabric between the sheets as screws will spool it up as they are driven in ,stay with the mat, Thickness ,a layer of 2 oz mat would be @ .060 .
     
  13. nomad821
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    nomad821 New Member

    what are the epoxy tube type in the caulk tube called and would they be strong enough to hold to the outer skin and then mat the sides and bottom with fiberglass
     
  14. gonzo
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    gonzo Senior Member

    It takes me less than ten minutes to wet mat on a transom repair. Lay the plywood flat, wet it, lay the mat, pout the resin over it and spread it with a brush.
     

  15. LMB
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    LMB Junior Member

    The epoxy I referred to is by West System called "Six 10". It is in a standard caulk tube with a metering nozzle that mixes the two parts as it is dispensed. I'm sure there are other brands. It's an easy alternative to mixing your own putties, though I admit I have not used it so far. I usually mix my own because I keep cabosil and fibers in bulk. Definitely strong enough, and the advantages would be the longer working time and easy mix/application. You can use it for gap filling and filets around the perimeter of the new core as well. Then glass the transom to the hull sides and bottom with adequete layers of fabric. Mat is not a good choice for epoxy though. I would stick with a resin system too - in other words don't mix polyester or vinylester application with the epoxy. It can be done but I wouldn't recommend it here.
     
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