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Author Topic: Epoxy didn't harden, here's what I did.  (Read 418 times)

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Offline Brad_bb

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Epoxy didn't harden, here's what I did.
« on: July 17, 2017, 12:22:16 am »
So I was filling a knot in a walnut board with clear epoxy (west systems).  I was using the slow hardener 207.  I don't have a pump for that one so I was eyeballing it.  That was my mistake.  I have been filling this knot my mixing in my little cups.  I mix one in the morning and pour it in and one in the evening.  Each cup fills it maybe 1/8 inch.  So I've been doing this for days maybe 15-20 times.  So on the last one, I must have mixed it wrong.  It would not harden.  It was thicker than when mixed- like warm taffy.  So I looked up on the internet if there was anything you could do to get it to harden.  Some products you can spray acetone or similar and get it to set up, but everything I read (mostly from boat guys) said that doesn't work with epoxy.  The only answer is to remove the uncured material.
   I didn't look forward to this.  I wasn't sure if that last layer could be removed without screwing up the clarity of my fill job.  So I used my knife and a shop towel soaked in lacquer thinner and started scraping off the uncured epoxy.  I used the towel to get the epoxy off the knife.  I went through a few towels and got all the epoxy I could scraped out of the knot.  I did my best to get  in the corners.  Then I poured some clean lacquer thinner in the knot to help dissolve the residual uncured epoxy, wiping it with a shop towel.  Having plenty of thinner is important so the towel doesn't stick and leave residue.  Believe it or not I got it pretty darn clean.  I then took my orbital sander with a new 80 grit disk and thoroughly sanded the surface of the hard cured epoxy, getting the the corners to remove any of the uncured residue that might be left.  After a thorough scuffing to give a good mechanical bond for the next layer of epoxy, I mixed up a cup with fast hardener for this last fill.  AS I poured it in I could see it fill all the scratches and the fill was CLEAR. 

I'm glad this worked because I had actually filled this large knot before using all fast hardener, and got too aggressive with how much was using and it over heated and got all cloudy.  I had to drill all the epoxy out and sand the edges.
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Offline Ianab

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Re: Epoxy didn't harden, here's what I did.
« Reply #1 on: July 17, 2017, 01:31:35 am »
I use digital scales from the kitchen to mix my epoxy. They are accurate to 1 gram (or about 1/25 ounce). So even with small mixes you can get the ratio right, 20 gm of A, 4 gram of B and it comes out right.
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Offline bucknwfl

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Re: Epoxy didn't harden, here's what I did.
« Reply #2 on: July 17, 2017, 10:22:50 am »
I have been blessed with good result from Rada and the calibrated pumps. I am glad it worked out for you I learned the hard way about over heating, mixing throughly and air escaping from pourous woods

Thanks

Buck
If it was easy everybody would be doing it