Making bottom of boat scuff resistent

Discussion in 'Boatbuilding' started by 300wm, Dec 10, 2015.

  1. 300wm
    Joined: Jul 2014
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    Location: Port Charlotte, Florida

    300wm Junior Member

    Hey everyone. Been a while since I was here. I got a lot of help from this forum with my first kayak build and have begun my second one. The first is 16'9" and made from 1/4" ply. It's a little heavy at 98 lbs, but it works better than I could have expected. This boat is going to my wife when I finish my 18 footer. I am still on a budget, so the wood I'm using isn't marine grade. I don't care about that...just by design, the boat will be strong. I want to paint the bottom of it with something that will make it scuff resistant without using glass (not doing glass!). I understand if there is nothing that will do it, but if there is, please tell. When I take the first one I built to the beach for rough water fun, I always have to touch up the bottom where sharp rocks have gone into the wood. Thank you for any help.

    MC
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Ouch, that's a heavy puppy. Xynole would be the best solution, but even more weight and the goo factor you're trying to avoid. This leaves a tough paint, which would be a true solvent based LPU, though it's going to get dinged up pretty easily from rocks. Truck bed liner will be tougher, likely the best paint like product you can use, but also some weight, as it goes down really thick (30 mils is normal), though not as heavy as Xynole.
     
  3. gonzo
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    gonzo Senior Member

    The traditional solution is a sacrificial wooden strip. When it wears out, you change it.
     
  4. 300wm
    Joined: Jul 2014
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    300wm Junior Member

    I could have gotten it to 70 lbs, but I went overkill on the stringers and bulkheads. I've weighed everything I need for the on I'm working on and it's at 48 lbs with no screws, glue or paint. 70 lbs for this one is my goal. The ply is 5mil hardwood laminate from Lowe's. I'm reading some resins will delaminate the stuff. Do you know if this is true or not? It doesn't need to be scratch resistant to large rocks or anything like that....just little sea shells at the beach that put nicks in the bottom that go to the wood. Reading and studying more, it looks like I will need to fiberglass at least the bottom. Any thoughts? If I sand the bottom with 80 grit and clean it well, will epoxy resin soak in enough to make a scratch resistant shell or is that a waste of time?

    Bed liner material is fine if it cures hard enough and will stick to wood...never thought of that.
     
  5. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Any paint-soaked fabric will do just fine. Try some scrap nylon sheer curtain fabric and fill with scrap paint - preferably a custom tinted oil based primer that gets sold for $5 a gallon because somebody didn't pick it up. It's going to take several coats, but so what. First coat has to be darn thin or the fabric will float.
     
  6. 300wm
    Joined: Jul 2014
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    300wm Junior Member

    Thanks. I did read, also, where drop cloth material works well for this. Do you know if acrylic latex will stick to oil primer? I hate asking simpleton questions, here, but it probably will save me from ten different opinions somewhere else, and I'm OCD.
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Cotton drop cloth is way too heavy to apply in paint and it also tends to rot. In fact, using paint to adhere a light fabric is about the weakest bond you can have, if used under the boat. Sharp rocks will easily tear it. Once upon a time, before waterproof glues and modern materials cotton fabrics were used, but only because they didn't have anything else. We have far superior products now and you'd be wise to employ them, unless you just like skinning the bottom of your boat each year or two with more easily torn fabric.

    Apply a centerline strip of 6" wide 'glass tape and do the same at the chines or at the bilge turn in round bottomed. This will be the lightest and most durable of the quick and easy methods. If you'd like more toughness use Xynole in the same locations, if not the whole bottom. If weight is a concern, use 'glass cloth instead which will require a lot less goo and will be 1/4" the weight of a Xynole sheath. Hell, a nylon fabric in paint, will be more durable than cotton.
     
  8. 300wm
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    300wm Junior Member

    OK...good tips, here. Thank you.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Truck bed liner will be the easiest, just roll it on.
     
  10. Barry
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    Barry Senior Member

    You could check out Gluvit, a two part brushable epoxy
     
  11. PAR
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    PAR Yacht Designer/Builder

    All epoxies are two (or more) parts and except for the fortified versions, all RTC's are also brushable, though using a brush isn't the wisest way to apply goo, except in small inside corners and crevices where nothing else will do.
     
  12. 300wm
    Joined: Jul 2014
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    300wm Junior Member

    This is the route I am going if the e-resin I have doesn't delaminate the ply I'm using. That was my main concern. I'm testing a heavily scored (60 grit) 12"x12" piece, now, to see if anything delaminates. I applied the second coat about an hour ago. It isn't fully hard, yet, as I'm using 50% of manufacturer recommended hardener. First coat took 12 hrs to get hard enough that I had to push to make a fingernail imprint (did that one yesterday morn). I'm thinking this will give me a good enough 'skin' to protect against little sea shells and such with sharp edges. Also, with the second coat, it has laid out smooth enough that I will only need to sand with 400 wet dry to get a good adhesion for paint. It really leveled out, nicely.
     
  13. Pericles
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    Pericles Senior Member

    I've always worked on the basis that if all else fails, then I should read & follow the manufacturers' instructions. Why would you use only 50% of the hardener? The chemists who created the formulae for epoxy resins decided in their infinite wisdoms that the substances you purchased will deliver the results necessary for your kayak to not de-construct, if you act sensibly.

    So, what do you plan to do with the surplus hardener you'll have left? Dump it or use with too little resin on the next project?

    https://en.wikipedia.org/wiki/Epoxy#Health_risks
     
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    If you've used 50% hardener, it's not going to cure (yep, never). You should never vary the resin/hardener ratio on epoxy. There's no way of fixing this, other than complete removal of all the incorrect ratio epoxy, grinding down to good, uncontaminated material and doing it again. I'm not sure why you found the need to do this, but before you play with any more epoxy, you should download the "user's guides" from WestSystem.com and the "epoxy book" from SystemThree.com and fully read them through.

    400 grit is a little too smooth for paint, unless it's intercoating. Primer will only need 180, with 220 being more than adequate. This will fill any minor surface imperfections, scratches, etc. 400 grit is getting into the polishing range and this isn't what paints like, for a good bond. The only time you'd use this fine a grit, is blocking down topcoats to really fine tune the finish. This is a wet sanding process to really smooth up the finish coats and unless you're spraying with an automotive style of process, absolutely unnecessary.

    Epoxy can't delaminate the plywood you're using, assuming it's an exterior or marine grade. Do some research before you continue and read up on the processes and recommended procedures, before you waste more resin or paint.
     

  15. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Ditto. The chemical reaction will never be complete. There's only one way to remove it, with heat and a scraper.
     
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