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Thread: Epoxy disaster

  1. #1
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    Default Epoxy disaster

    Hi all, I tried filling a hole about 10mm deep in a stair tread and everything seemed to be going fine until smoke started coming off the epoxy. It was fully transparent and bubble free (I was hitting surface bubbles with a flame). I am curious as to why it went pear shaped? I used west systems epoxy. A heap of bubbles formed on the very bottom of the cavity I had filled as it went off. My only thought is to now file it down and epoxy over the top of it with some black mixed in a new batch? Any help is greatly appreciated.

    15342445180910.jpg

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  3. #2
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    I have seen that happen before with fibreglass resin when too much catalyst was mixed in. It started to smoke and bubble up all of a sudden.

  4. #3
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    the epoxy curing reaction is exothermic -- i.e. generates heat.

    too great a volume of epoxy can result in enough heat to start a fire adding heat to remove bubbles also raises the heat of the reaction

    cautions include

    limiting the mass of epoxy in any one place, fill in layers rather than all one go

    using an epoxy mix that cures more slowly -- usually the hardener can be tweaked to force a longer cure time
    regards from Alberta, Canada

    ian

  5. #4
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    Woodturning?

  6. #5
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    Some epoxies are better for filling big holes than others. I have used West System for making and repairing boats and loved it, but when I have a big hole to fill I use Bote-Cote Pacific Epox-E-Glue. It starts as two thick pastes (A and B) and you can add spirit dyes or powdered colouring to get the colour that you want. Because it is such a thick paste to start I have never had any problems with it. It also doesn't sag if filling a hole in something vertical.

    I'm pretty sure they sell online though have always purchased when I've seen it at wood shows.

    Good luck
    David

  7. #6
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    Very timely for me, as I'm about to start converting a large blackbutt slab into a coffee table - first up, many cracks and voids to be filled with epoxy.

    For those who use West System, which resin/hardener combo is best for this? I'm assuming that the slow curing hardener will also reduce the exothermicosity (ahem....) during cure? What tinting materials are compatible with the West System stuff? For this project I'll go with black/dark brown, but for other projects I like the look of electric blue, etc. I've seen in various YouTube vids. What tints can be purchased to achieve this? I'll have a look at the Bote-Cote stuff recommended above as well, thanks for the suggestion. I've already seen dire warnings of tape on the bottom of a slab sagging under the weight of epoxy, so some support clamped to this is probably a good idea whatever epoxy I end up using. Any advice much appreciated - first time working with a slab for me !!

  8. #7
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    Quote Originally Posted by Mr Brush View Post
    Very timely for me, as I'm about to start converting a large blackbutt slab into a coffee table - first up, many cracks and voids to be filled with epoxy.

    For those who use West System, which resin/hardener combo is best for this? I'm assuming that the slow curing hardener will also reduce the exothermicosity (ahem....) during cure? What tinting materials are compatible with the West System stuff?
    I use the Feast Watson Prooftint. It only takes a few drops to change colour to a solid black.

    I used to use the 205/206 hardener. I bought the 207 hardener which doesn't darken with age and also has a longer cure time (15hrs or so). It's a little more expensive but the benefit for me is worth it. For large pours, WS might not be the cheapest.

  9. #8
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    Thanks for that lewisc - just what I need to know. I happen to have plenty of Prooftint in a selection of colours, so will experiment with some small mixes first.

    I'm still considering whether it is worth getting a proper vacuum degassing setup for working with bulk epoxy; there are some fairly cheap options available on evilBay, e.g.

    https://www.ebay.com.au/itm/2-Gallon...oAAOSwaWNZh7-S

    I plan to play around with burls filling the voids with bright-coloured epoxy (electric blue, orange, etc.), so the vacuum setup would get more use than just one slab table.

    Has anyone purchased/used anything like this?

    Cheers

  10. #9
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    I should add that the blackbutt slab in question is quite big.....

    IMG_0106.JPG

    Almost 2m along the long axis, about 650 wide. I still have to decide what shape to put on the part sticking out the side - it needs to be rounded off in some way, also probably put a slight curve on the short straight end. First job is to get all cracks and voids epoxied to make the slab completely stable before I start hacking at it

  11. #10
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    Looks like 105 resin plus 207 hardener might be the go

    https://www.westsystem.com/207-special-clear-hardener/

    Some interesting tips for new players there - e.g. making a hole in the bottom of the mixing vessel which can be opened up to dispense epoxy. This should avoid using the bubbly bit on top of the mix. Also pre-coating surfaces before a bulk pour, and warming things up a bit to help bubbles come out.

  12. #11
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    As Ian mentioned, the epoxy curing reaction is exothermic - it generates heat. The hotter epoxy gets - the faster reaction goes - more heat generated and the reaction goes even faster - thus it starts "boiling" and generates all those bubbles. My guess will be that you heated it up too much, and the chain reaction started. I used West Systems to fill large holes (much larger than what you show), and did not have problems. Once it was cold (Canberra winter night), and I decided to warm up the container where I was mixing it with a heat gun, and had the same effect, it even melted through a plastic container. So I am usually trying not to over-do bubble elimination with the torch to avoid this.

    BTW, the mixed epoxy can be stored overnight in a freezer (just make sure that the container is closed, or epoxy will get milky if water gets in), and then slowly warmed up and used again.

  13. #12
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    Instead of using epoxy, why not use polyester casting resin. Its cheaper, has a long cure time and you're not mixing a very small amount of catalyst with a large amount of resin, so it's easier to get the correct ratio.
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  14. #13
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    Quote Originally Posted by AlexS View Post
    Instead of using epoxy, why not use polyester casting resin. Its cheaper, has a long cure time and you're not mixing a very small amount of catalyst with a large amount of resin, so it's easier to get the correct ratio.
    Any compatibility issues with West System or similar Alex?

    George

  15. #14
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    Quote Originally Posted by cava View Post
    Any compatibility issues with West System or similar Alex?

    George
    That I don't know, although I suspect not. I've only used it to fill large voids in wood.
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  16. #15
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    Sorry to hear about your disaster. Next time, it might be a fair idea to try an experimental piece first before going live.

    mick

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