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Thread: first slab with epoxy - and a question

  1. #1
    Join Date
    May 2015
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    NW Indiana
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    first slab with epoxy - and a question

    My wife went with me to Cassen's a couple months ago and found a walnut slab she wanted for a small coffee table. Used a router sled to flatten it and then epoxy to fill the voids. Used M&T's and dowels to attach the legs. She wanted a hint of a tree limb somewhere, so the shape of the stretcher. All in all it came together pretty well. But after the first coat of wipe on poly I got the light specs you see in the last pic. Are those air bubbles I missed. Used a torch to raise them - maybe didn't get them all? Any way to address them now and fix them? I read that sometimes you can use a scraper to get them out. I'm all ears for suggestions.
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  2. #2
    Join Date
    Mar 2003
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    San Francisco, CA
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    8,730
    Yes, those look like bubbles from air caught under the epoxy as you poured it in. You might be able to dig through them with a scraper, but then you'd have divots in your finished surface. I'd use a vacuum cleaner to try to remove most of that white dust in the holes, then add more epoxy to fill the holes. Fortunately, epoxy bonds well to itself. Overfill the holes a bit to make sure you have them filled. Wait for the new epoxy to cure, then use that cabinet scraper to remove the excess. Sand and varnish from there.

  3. #3
    Join Date
    Apr 2013
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    Issaquah, Washington
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    1,138
    Bill,
    I don't see how a scraper is going to help at all. Typically a scraper is used to remove the overfill excess flat to the surrounding surface. Your air bubbles appear to be trapped below the surface. Drill down to the bottom of each one with a bit that is sharp and has a diameter equal to, or slightly larger, than the bubble, blow out the residue and fill with epoxy using a syringe.

    Done properly there will be virtually no sign of repair.

  4. #4
    Join Date
    May 2009
    Location
    black river falls wisconsin
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    766
    i would use the vacume. i also have had luck with a awl point. seams a scraper might do more damage than good. I like the look of bench.
    Last edited by eugene thomas; 05-26-2019 at 4:32 PM.

  5. #5
    Join Date
    Mar 2008
    Location
    SW Michigan
    Posts
    390
    I second Bill's advice. I like the X-shaped leg, adds a nice visual touch and still goes with the "rustic" live edge looks.

  6. #6
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    161
    The only bubbles I see are in image of 7 of 7.

    If I were to try that with West system epoxy, the only ones I have used, I would likely first heat the wood surface with a heat gun, apply goop liberally to hot wood, then withdraw the heat gun and let the epoxy sure on a cooing substrate. Wear a respirator with organic solvent filters for that stunt. Once all the end grain down in that hole is plugged up and well cured I would reheat the surface of the cured epoxy and pour it about half full, let that go a day and then repeat.

    I mostly follow Robb White for using epoxy. He was a bit of a non conformist, outside a lot of classical norms, but he was a smart dude who did a lot of his own data collection. I recall him quoting a USAF experiment form the 1950s about helicopter blades. if the wood is heated after the epoxy is on, the epoxy bubbles as it cures - and the helicopter rotor comes apart in the air. If the wood is heated enough first, the wood cools as the epoxy cures, sucking the goo down into the wood. IIRC he did a lamination on the cutwater for a skiff and got 5mm facegrain penetration without a vacuum setup.

    Remember epoxy curing gives off heat, so the wood wants to be pretty hot. He (Robb) liked +130dF when applying epoxy to cedar or poplar. I don't know that he used any walnut in boat building.

    Otherwise the table looks great. I would drill, then heat the cured epoxy (organic solvent filters) with a heat gun, then inject with a syringe.

    The one thing I have read over and over is do not sand epoxy until it is fully cured. Something about permanent irreversible lung damage.

  7. #7
    Ditto on the drill-and-fill-the-bubbles recommendation. I've used that before with good results.

    Also, nice design on this! I like what you've done there!

  8. #8
    We do way to much of this at my job. Get at the holes with a wire brush, blow them out, flood with alcohol, then blow out again. after this recoat with epoxy and heat to bring up air. The original bubbles were probably air exiting the actual wood during the cure. It's a good idea to precoat larger pours to seal in moisture and air.

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