Epoxy mistake

[DC]

 I epoxied a backing on yesterday using West 105/205 and I must have mixed it wrong because today about 18 hours later it's still rubbery. Should I take a chance and let it set for a while or should I heat it off and do it properly? I think I just answered my own question . I've done a lot of these and this is the first time it's done this so I'm sure I did something wrong.

[DC]

I called West and they said peel it off. If it isn't hard in 18 hrs it ain't going to get hard'

[gutpile]

my answer exactly

[sleek]

West is GOOD stuff. I use it when I build wooden boats. Literally trust my life with it.

[DC]

It took 2 minutes to strip off the boo. I actually think it would have pried off without heat. I use hypodermic syringes to measure small amounts of epoxy. I usually make 5cc of resin and 1 of hardener. This time I wanted more and I think I did 10cc and 1cc instead of 2. The worst part was that now the uncurable eoxy had soaked into the wood so I had to scrape and then resand everything. I just hope I took enough off. It's all done, tomorrow will tell.

[DC]

I put the leftovers from the failed batch and the leftovers from this mornings batch on the hood of the car about 3 hours ago. Today's batch is hard and yesterdays is still rubbery. I did the right thing by starting over.

[Hamish]

Like you said it was probably a mixing mistake.
I have used West Systems over many years, for woodworking, and really like its versatility. I still use it for woodworking today. That being said I have had issues with West systems with bows. 1, full length delamination of bamboo on a backed bow at the start of floor tillering. 2. Glued on risers lifting at the edges. That was about 15 years ago, they might have tweaked their formulas since then.
         I tried known bowmakers epoxy like Techniglue(Australian high strength structural adhesive) and have had no problems whatsoever, with delams, or lifting risers. I know plenty of guys use West's for bows, and seem to get decent results, but I won't bother because proven bowmakers epoxies like Smooth On, and Techniglue dry so much harder, and they won't delam as easily.

[PatM]

 What are the numbers of the two types of Epoxy? It might be the opposite  of what you think that's caused your problems with it.

[willie]

Hamish, If I mix some cabosil with the west laminating resin, to where it has the conststency of smooth-on, it wiil be rock hard also.

DC, I mix small batches by weight, all into the same cup.

[PatM]

West cures like rock on its own too.

[DC]

What are the numbers of the two types of Epoxy? It might be the opposite  of what you think that's caused your problems with it.

I do have 205 and 206 hardener but I keep the 206 way in the back of the shelf and it's still there(I just checked ). I only use it if I want a very clear joint. 205 darkens with age, 99% of the time I don't care. Even considering that the 206 would have been hard by now. I'm confident I could take today's glueup off the caul now but I'll leave it til tomorrow. I just screwed up. First time in years of mixing this stuff, hopefully the last although I am getting old. I was just informed That I'm going to be a great grandfather in Dec(puffs out chest)

[PatM]

 West does seem to have higher numbers.  The problems seem to be more likely because it won't move like Smooth-On  does.

 You can look the numbers up and compare.

[Tommy D]

I would recommend buying a grain scale to mix small batches of epoxy. Epoxy is incredibly sensitive to getting the mix exactly right. I believe something as small as 3% off can cause problems. So the smaller the batch the more likely that any measuring mistakes, unmixed hardener left in the syringe etc will be amplified.

[Tuomo]

Epoxy is incredibly sensitive to getting the mix exactly right. I believe something as small as 3% off can cause problems.

Not every epoxies. From Technical Bulletin of Smooth-On EA40: "Mix ratio is 1:1 by volume. When mixed 2A:1B by volume, EA-40® will achieve greater heat resistance and improved physical properties.". So, not really sensitive. When there is more part A than part B, then everything is fine. Of course there are mixing ratio sensitive epoxies but why one should use them?

[PatM]

The ratio for West does have a bit of leeway, not that much though.

 System Three G2 also has a variable mix ratio.

My best screw up with West involved absentmindedly using five pumps of resin to one of hardener.  Using pumps that were calibrated to  deliver 5:1 with a single pump from each can.