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  1. #121
    hi

    The mixture will certainly start of with a lower viscosity if it's warmer but it will also set faster as well (a rule of thumb from chemistry is a reaction will go twice as fast for every 10 deg C warmer)

    I havent read the manuals on these yet, but

    i suspect that this would be an
    exothermic reaction, ( , or endothermic ). If so, it might not react properly outside the recommended temp, and the suggested temp, may be the temp that it hardens the best at.
    The rule of thumb mentioned above in the quote, would generally only apply to a stable compound, not a 2 part mix, especialy if that mix is exo or endo thermic

  2. #122
    I would put money on the reaction being exothermic. The epoxide ring is high strained configuration and and therefore would be expected to release a significant amount of energy upon opening. The other reactant is generally an amine and hydrogen can be made to fall off them quite easily normally (fall off being used in the technical sense here ;-) ).

    From a chemistry point of view temperature generally only affects the speed of the reaction (within reason, you obviously get different products if the reaction catches fire). There are reactions where the end products you get are dependent on the temperature of the reaction but they aren't very common and I don't think that would be the case here as this chemistry is "aggressive". My guess is that this is more of a mechanical issue. To produce a strong end product the amine hardner needs to be able to cross link the epoxy. If the mixture is cold the molecules won't be very mobile so it's less likely the amine will bump into and be able to link to more than one epoxy leading to a product that is mechanically quite weak. The lower the temperature the worse this would be.

  3. #123
    Quote Originally Posted by Clive S View Post
    Are you going to make a moat between the two rails so that they will be both at the same level, also the epoxy will rise up at the edges so make sure you have a wide enough flat plane to mount the rails on say at least 10mm each side. ..Clive
    Yes, maybe one each end, I will leave 10mm each side.

  4. #124
    I realise there will be some heat generated by the mix but do you think the draught excluded can retain it ?

  5. I've used a fair bit of epoxy (usually thickened, though) for various boat repairs in the past and I can confirm that it is exothermic from personal experience. Fine in a wide, shallow, container but in a tall, narrow, container on a warm day - the pot was starting to smoke after a few minutes and it also starts setting much more quickly as it warms! For levelling, though, and assuming that it doesn't get too hot in the mixing pot, you are going to be putting a thin layer on a metal surface at ambient temperature so I doubt if temp will give problems; my guess is that viscosity is more important than setting time here, as long as it has time to run before it starts to gel.

    As a solvent, epoxy resins don't seem to be as aggressive as, say, polyurethane resins. I used some small plastic pots for weighing out and mixing epoxy with no problem; first time I did the same with a 2-pack polyurethane, it went straight through the pot, the plastic tray I was using to catch the drips, and although the scales were metal and wiped clean, the stuff didn't do much for the plastic cover over the display which isn't quite so easy to read any more. My guess is that you are probably OK with the rubber sealing strip, but it would be easy enough to test a little bit first, maybe.

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  7. #126
    Quote Originally Posted by EddyCurrent View Post
    I realise there will be some heat generated by the mix but do you think the draught excluded can retain it ?
    A 5mm layer of epoxy isn't going to generate enough heat to warm up a big chunk of metal far enough to generate any problems. Don't wait too long before pouring it though as it will generate heat in the pot.

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  9. #127
    In fact when i mixed and poured the West System just 2 days ago, outside was around 19C. When i mixed it, for a second was a bit worried about the quantity i mix, but nothing happened. No heat at all.

    Epoxy also suffers from humidity, i know this, as i live at 90% humidity near the sea.. So most epoxies i have used before/marine grade usually/ dried with a kind of mattish surface.

    In the pdf says that the WS has no problem in high humidity working area.

  10. #128
    Quote Originally Posted by Clive S View Post
    Are you going to make a moat between the two rails so that they will be both at the same level, also the epoxy will rise up at the edges so make sure you have a wide enough flat plane to mount the rails on say at least 10mm each side. ..Clive
    Clive, would you say it was easier to drill and tap all the holes for the rails after doing the epoxy?
    Neil...

    Build log...here

  11. #129
    Quote Originally Posted by njhussey View Post
    Clive, would you say it was easier to drill and tap all the holes for the rails after doing the epoxy?
    I take it that you have seen the pics that I posted. When the mdf sides were taken away you will find that the epoxy has crept up the sides a little. I then used a flat file to scrape the high sides away just until you see it marking the centre. I left mine to cure for about 3 days before removing the mdf. I just drilled through the epoxy and steel and then threaded in the normal way. It was way easier than I had thought.

    When mixing the epoxy I did it by weight, I was told by the very helpful people at Wests to mix it in a wide container as that would produce the least heat. There is no problem with mixing it in one or two batches, I also used a hot air gun to flash the surface after it was poured to get rid of any bubbles in the surface. I believe that the proportions of the two part mix should be done accurately . Hope all this helps biggest tip is sealing the moat for leaks before you start as that will give you problems. ..Clive

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  13. #130
    The epoxy came today, only ordered it yesterday...nice!! Anyway, got it out of the box and gave it a shake to see how viscous it was. Not too bad and should pour quite nicely. I'm going to experiment with a small bit of steel and see how it mixes and settles between a couple of channels.
    Neil...

    Build log...here

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