Thinning Epoxy?

Discussion in 'Materials' started by Frog4, Oct 17, 2011.

  1. lewisboats
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    lewisboats Obsessed Member

    When using epoxy, clamping pressure is used to keep the parts together only. If you use too much pressure you squeeze all the epoxy out and get a starved joint.
     
  2. tunnels

    tunnels Previous Member

    Clamping pressure has everything to do with a glued join .:confused: The thickness of the glue film is very important . PLUS clamping helps to impregnate the pours of the wood fibres and so the glue gets further into the wood ,Too much pressure and the glue is the weak part of a join . Not enough and you have a slight gap filled with glue and looks unsightly .
    Think in moderation !! always !!:idea:
     
  3. sabahcat
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    sabahcat Senior Member

  4. CC Guy
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    CC Guy Junior Member

    This may be of interest as I have run some simple tests to see how much I can soak wood with epoxy.
    This is 2mm mahogany coated in thinned epoxy as the maker recommends on one side only.
    ceps_1.jpg

    ceps_2.jpg
    Back side.
    ceps_3.jpg
    Still not happy with that I thinned it more to 75%

    start_099.jpg
    Back side.
    start_100.jpg
     
  5. lewisboats
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    lewisboats Obsessed Member

    But what have you done to the properties of the epoxy itself?
     
  6. CC Guy
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    CC Guy Junior Member

    In my case I'm using it as a deep sealer before a coat of unthinned epoxy but letting it fully dry to avoid thinner entrapment and with a light sand between the coats.
    I think you guys call it CEPS but by mixing my own it much more cost effective.
    A friend sent me this link about CEPShttp://www.epoxyproducts.com/penetrating4u.html
     
  7. PAR
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    PAR Yacht Designer/Builder

    It will not seal anything, nor will it have anything remotely close to the physical properties necessary, to prevent moisture vapor transmission into the substrate. Stopping moisture vapor transmission is the key here, not how deep the goo gets.

    Once again, tests (repeatedly) have shown that substrate penetration hasn't anything to do with moisture vapor resistance. It's the quality of the coating folks, not how far it soaks in. If the coating lets more then just a few percent of moisture absorption (typically 30 day, full immersion test), then it's not going to stabilize the substrate's moisture content, hence it's not waterproof, nor sealing.

    A 25% dilution of standard laminating resin will reduce the physical strength of the cured goo by well over 50%! You can just imagine what happens with a 75% dilution, zip for physical strength and no stiffness at at all. So, subsequent coats of full strength epoxy are relying on a bond with a well penetrated, but hugely weaken epoxy mixture. How good do you think this grip might be? In fact, you'd be better off epoxying over an LPU paint, because it has better moisture resistance and sheer strength then the heavily thinned, but well penetrated epoxy!

    The simple truth is the hot on hot method is the best way to get a substrate well coated with epoxy. The cooling air inside the wood cellular structure contracts, which sucks the resin into them, sealing it for good. Couple this with sufficient film thickness (about 10 mils), which 3 coats will provide and you've effectively sealed the wood.

    We can get technical and talk about the relative size of the epoxy molecule and it's ability to penetrate a substrate, but again, it's not about penetration, but coating quality (and thickness). If you feel you need more protection, this is what reinforcements (such as fabrics) are for.
     
  8. sabahcat
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    sabahcat Senior Member

    An Observation

    I did some samples for my previous boat where I used AA grade hoop pine ply for the side decks.

    In both samples I used plain weave glass and pure epoxy

    In one sample, I used a primer coat of epoxy thinned with Industrial Metho (Ethyl Alcohol) @ approx 20ml to the litre before using pure epoxy and glass for finish.

    In the first sample (pure epoxy) , the glass was able to be peeled away relatively easily with small fibres of wood coming away as well.

    On the second sample (thinned with metho) it was much more difficult with the glass tearing and where I was able to pull off glass, much more timber came with it.

    Like I said, that was my personal observation using one brand of resin and ply.
     
  9. Frog4
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    Frog4 Proletariat

    thanks PAR ...
     
  10. CC Guy
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    CC Guy Junior Member

    Hi Par, thanks for your thoughts on this, as I understand your points all hinges on a 10 mils coating that will never be broken which may work for you but many of us live in a less perfect world where knocks and scape's do happen.
    Should the 10 mils coating be broken the wood will be exposed to moisture followed by rot /discolouring deep epoxy would help protect the wood the moment the outer coating is broken.
    As for using a fabric layer over again this can be damaged and cloud over time.
    As for less strength, the key here is sanding as I stated, not as you imply coat on coat, which will uncover the top wood fibers for a good bond will it not?
    If your using laboratory data for your premise this can be misleading as its not the real world.
    I'm no chemist but are all epoxies the same the world over? I would like to see some accurate data on the the good and bad from around the world.
    Please provide us with actual boat field study that recommend only a 10 mils clear epoxy coating for total protection over many years which includes damage to the surface.
    CEPS is not just about moisture protection,there are other benefits I can see but have found one drawback that you have failed to mention.
     
  11. Steve W
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    Steve W Senior Member

    It should go without saying that when you damage a coating, be it on wood, steel or whatever, you repair it right away, it is pure fantasy that thinned epoxy will penetrate deeply into the wood, it is only marginly more than 100% solids epoxy. As has already been mentioned, apply the epoxy when it is warm and when the temperature is trending down, not up and you will get good penetration with 100% solids. If you apply when it is hot and trending up you will get the opposite effect with outgassing and blow bubbles in the coating.
    Steve.
     
  12. latman
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    latman Junior Member

    I never add anything to thin epoxy , just rely on the formulation and temperature .The thinnest epoxy would be one formulated for infusion.
     
  13. PAR
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    PAR Yacht Designer/Builder

    Even the best penetrating epoxy doesn't get very far into many types of woods and plywood has a WBP glue line that stops it, so (again) penetration means nothing in regard to moisture stabilization or waterproofing.

    Of course you get dings and nicks, but if you expect a penetrating epoxy to compensate over your neglect of the surface, then I'm afraid no material, coating or magic goo in a can is going to help you. Having a few more mils of penetration means absolutely nothing if you bash into a dock.

    CC Guy, I am a chemist, at least that's what they said at the U of D, as well as a structural engineer. You can talk about unsubstantiated marketing hype (like the CPES folks) or you can actually preform the tests and/or look the data up. Most of the major formulators have done this, including a few linked in this thread, so frankly

    preform your own research, buy into the hype or do the tests yourself.

    There's nothing that CPES does, that can't be done better and cheaper without it. CPES is a pure marketing product and they've made millions off of their advertising (which they've been forced to changed BTW) and their profit margin is huge, considering what you're getting. You'll pay about 200% for the actual epoxy resin in their product, not to mention the 500% markup on the contradictory combination of dilutes employed. You don't even want to get me started on this product and I'm just one of a long list of people that have "figured it out" about the Smith Brothers.

    It's telling when all the major formulators say don't thin your goo, yet, you and the Smith boys have a better idea.
     
  14. CC Guy
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    CC Guy Junior Member

    Hi par thanks for just your opinion I see no study links to back you thinking other than missing the issue by adding ply into the equation,to which I was working on given the glue line problem hence the 2mm mahogany above that you seem not to see.
    As for test this is where I am, coated both side with 75% thinned epoxy then sanded and bonded together with unthinned epoxy giving me a ply which I cut a sample with all edges sawn leave all out side faces uncoated other than the thinned epoxy by 75% I placed under water with weight on top and left for 3 weeks
    after which I measure the thickness which had only increased by .3mm

    The down side I can see with this is if staining it must be be done before thinned epoxy is applied and found that the sample I made was now neutral buoyant.

    Please post your hard data not your opinion so I can compare to check mine.

    start_118.jpg
     

  15. Frosty

    Frosty Previous Member

    Ok heres a dumb question , what would happen if you applied a coat of epoxy without hardener and left it for a few days then a coat of epoxy with hardner.
     
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