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Thread: Epoxy coverage

  1. #1

    Default Epoxy coverage

    Hi all,

    Iíve used epoxy for taped stitch and glue canoes before but not for completely covering an entire hull of a canoe. Can anyone give me a rough guide on how how much epoxy (in kg) it would take to lay 4oz cloth (1 metre wide, 4 metres long), with enough coats to pretty much fill the weave?

    Thanks in advance, Adam.

  2. #2
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    Different epoxies have different coverage depending on how thick they are, but as a rule of them when laminating carefully with a suitable laminating resin, you want to be aiming for about the same weight of resin as cloth, no less. For an inexperienced hand laminator you will probably use a bit more than this, and if you are aiming to completely fill the weave you will need more again.

    Considering the properties of epoxy you have a few options. The properties to note are that it is sensitive to UV degradation and it cures with a waxy amine top coating which can be sanded away but you will never get as good a bond between coats once cured as you will when it is still tacky.

    The first coat will not fill the pores in the cloth flush.

    - You could use a resin specially formulated for coating with UV inhibitors in it (like Easycomposites XCR or West 207) and make sure you overcoat within the tacky window until you get the surface flat. XCR can be wet sanded after curing for a good finish, probably 207 can too.

    - If you use a regular laminating epoxy you can lay peel ply over the resin whilst still wet and rub it down into it so some resin seeps through all over. When cured you can peel the peel ply away taking the waxy layer with it and providing a much better bond for a subsequent coat than trying to sand a highly textured surface. Ideally you will sand the final coat and apply PU varnish or similar for UV protection, but for boats normally stored indoors a lot of people don't bother. You could also switch to a coating resin at this point, or use peel ply with coating resin if you can't make use of the overcoating window.

    - The final option which will likely be more prone to cracking, is to use gel coat for the final layer ideally after using peel ply on the epoxy. There are epoxy gel coats available now, I haven't tried them, but I have used polyester gel coat quite successfully on slalom boat repairs. Polyester really doesn't bond well to epoxy so will likely chip off if you are likely to knock it around a bit, but I recently used it on the bottom of a Wild Water Racing C2 that needed extensive repairs - I essentially sheathed it with a 5m x 1.5m glass cloth instead of trying to do individual repairs. That took 700g of polyester gelcoat mixed with 2% wax in styrene to make it cure in air. The biaxial cloth I used is particularly coarse and I didn't quite fill all the pores flush (it is to be a training boat), but after wet sanding through the grades and polishing I achieved a good smooth glossy finish albeit not entirely level. It hasn't had much use yet (10 minutes test paddle on flat water) so I can't say how long the gel will last. It lasts pretty well indefinitely on slalom boats which are very stiff, but the flexibility of the WWR C2 will likely allow it to chip/flake.

    How hard can it be?

  3. #3

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    Thanks for the detailed reply, that will help me quantify what I need... I like the idea of the easy composites stuff, perhaps not the xcr as it comparable price wise to the west (and I have access to that locally), but the EL2 looks very reasonably priced. Have you any experience of that? It will be either varnished (ideally) or painted so that will hopefully give UV protection. Thanks again

  4. #4
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    Yes I used EL2 on glass cloth for the WWR C2 I mentioned above, to be completely accurate I bought a couple of the 1kg split hardener packs and mixed the hardeners to give an intermediate cure time to suit the temperature and how long I expected the job to take! I found the EL2 just as easy to work with as West and the ability to custom mix the hardeners has come in useful a few times - I have never noticed anything in West datasheets suggesting you can mix the hardeners for custom cure times, but it might be possible?
    Only issue with easycomposites resins is that they are mixed by weight rather than by volume like West and others, not a problem for large batches for sheathing, but when I am doing small 10 or 20g mixes for small repairs I find my scales are not accurate enough to get the ratios spot on - solution is to buy better 'micro'scales to repalce my kitchen type scales, which I keep meaning to do!

    How hard can it be?

  5. #5

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    Excellent info, thanks. One last question... did the EL2 have a noticeable tint to it (planning on vearnishing over the top)?

  6. #6
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    No, one of the hardeners has a bit of a tint, but once cured there was no tint.
    You may not have permissions to view this, but it is a shot of the C2 after I had clear gel coated, sanded and polished it on top of the EL2/biaxial glass layer, which is actually on top of the new bits of kevlar which are a good indication for lack of tint. The old kevlar is much darker, the new stuff looks the same colour as when it is dry.


    How hard can it be?

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