Fiberglass repair dilemma

Discussion in 'Fiberglass and Composite Boat Building' started by Tiny, Jul 18, 2010.

  1. Tiny
    Joined: Jan 2009
    Posts: 10
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: UK

    Tiny Junior Member

    Hi
    I am trying to decide if I need to do a full laminate replacement job here, or if new gel coat will fix it. See attached photo. The boat is a Laser. There is cracking visible in the fiberglass, which has gone white. The area is about 4" across. There are other areas on the boat which have stress cracks, but this area was definitely the worst. I have uncovered the underlying fiberglass in a couple of these areas and the fiberglass seems comparatively sound.

    The damage has occured due to the boat bouncing up and down on a badly fitting trailer, we can assume the cause has been cured.

    The aim is to not have to revisit this job again.

    The question is, do I need to cut out the cracked area and replace the laminates, or will trying to force some resin (epoxy, polyester, gelocat?) into the crack, and re-gelcoat do the job.

    For:
    If the bonding of new material is successful, structurally, we wont have to revisit this.

    Against:
    If the bond isnt perfect the result is a weaker boat.
    Lack of continuity of fibers will result in a weaker boat.
    It will be difficult to get the hull as fair as it was originally
    Its right next to the white stripe, so getting that line back in gelcoat, for a good cosmetic finish will be almost impossible.

    Any advice very gratefully accepted.
     

    Attached Files:

  2. tinhorn
    Joined: Jan 2008
    Posts: 575
    Likes: 20, Points: 18, Legacy Rep: 310
    Location: Massachusetts South Shore.

    tinhorn Senior Member

    I certainly wouldn't cut that chunk out--it'll make patching more difficult.

    I've never worked on a Laser. Can the deck be separated easily (like drilling out rivets) or are the deck and hull bonded together?

    I like to patch from both sides, and in some cases will grind away about half of the impact damage, patch one side, then grind away ALL the rest of the impact damage from the other side and complete the repair.

    If you can only access the outside of the boat, try to leave 'glass about the thickness of a cigarette paper. Really, you want only as much garbage left as it will take to help shape the patch. Follow each of those cracks out to their ends and let the grinding pad go through the 'glass at the end of the crack--kinda like stop-drilling a crack in metal or a windshield.

    (I've followed those darned cracks for over a foot when I'd originally anticipated maybe a three-inch patch.)

    Don't worry about the paint line until the boat is soundly repaired. You're gonna have more trouble matching the yellow color than separating white from yellow. I'd paint the whole patch white, then apply regular painter's masking tape to create the paint line. Pull the tape off while the gelcoat's wet.

    On truly ugly patches I'll often apply just one thin layer of mat, with minimal resin. (You'd be surprised at how little resin it takes to wet out mat.) That first layer will hold the shape for subsequent layers (and serious rollout), but you want to be sure to sand it completely before applying the additional layers of glass. I've bought "wax-free" resin that contained wax. If there is not enough old glass to shape the patch, stick a layer of woven cloth--10-oz. or so--between two layers of thin mat and ROLL IT OUT ON THE TABLE to remove the air bubbles from between the layers. Apply, poke, prod as necessary.

    Under no condition expect new 'glass to stick to the old surface without grinding it back to fresh stuff. If your patch DOES extend onto the old surface, don't panic--just make sure you grind it back after it cures. If you can see the line between old and new, you can see where your patch will start unraveling.
     
  3. Tiny
    Joined: Jan 2009
    Posts: 10
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: UK

    Tiny Junior Member

    Thanks for your advice Tinhorn.

    So, can I assume it is necessary to undertake a full laminate repair?

    My plan in which case would be to make a cured 'glass pad, and bond this to the inside of the hull (which I cannot get to). i.e. lay up some glass (with apreg 21 epoxy) over some polythene on the outside of the hull, cure, trim to size, then cut out the cracked stuff and bond the new bit to the inside of the hull with plenty of epoxy goo. Getting the pad through the cutout by bending it, and holding it in place with a piece of string to a self tapper in the middle of the cured bit. Finally, layup new 'glass over the bonded in pad and scarfed edges of the hole, gelcoat to finish.

    I like the idea of thickening the hull slightly in this area, to stiffen up.

    Can I assume I wont have problems bonding epoxy to polyester, and gelcoat to epoxy?

    The remaining, less well developed, cracks, I plan to chase out to their ends and fill with gelcoat.
     
  4. tunnels

    tunnels Previous Member

    The repair will have to be bigger than just the part with missing gel !!.All those stress cracks that are showing in the photo will need to go as well because the crack tell theres damage below the surface .
    Just grinding , filling and regelling the cracks ! then they will return at a later day for sure , Theres damaged glass below the surface !!.
    If the boat was built of polyester resin then use poly to repair it with !! Or Vinylester which is a better quality resin . Careful using woven or stiched cloth ,it could print through in the yellow zone as it will draw a little more heat when its out in the sun and the resin will shrink more that the white area !!!. :p :D :p
     
  5. mark775

    mark775 Guest

    Tiny, how much of the hull is like this? can you give me a percentage or complete photographs?
     

  6. Herman
    Joined: Oct 2004
    Posts: 1,618
    Likes: 89, Points: 48, Legacy Rep: 1240
    Location: The Netherlands

    Herman Senior Member

    As being a Laser, slightly overbuilt, and with the assumption that the boat is allowed to look used, I would just grind away that 4" patch, and leave a bit of laminate behind. Then fill with CSM and poly resin, grind again, to be able to apply gelcoat, and top the patch with gelcoat. (along some tape for the white patch). Then sand and buff.

    So not too difficult. Some cracks might pop up later in the area that was not checked / repaired, but even that I doubt. Lasers are not highly loaded.

    Oh, and the deck will not pop off easily, it is bonded pretty well. It is not even easy to cut it off, due to the gunwhale design.


    As you will have plenty of poly resin and chop left ( :) ) I suggest making a nice trailer mould, so the boat has plenty of well formed support and will not have trouble again. Wax the area where the mould sits on the boat. protect the rest. (tape and plastic). Apply some 10 layers of mat, let cure after each layer (the first 4 layers) and after each second layer (the rest) as not to introduce too much heat in the boat. Demould, clean up, and replace on the boat. Now place the trailer on the boat (upside down) and laminate the supports that should hold the trailer moulds to the mould, to the actual moulds. (or create some other solution). Glue plastic grass to the mould. Presto!
     
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