Sunday, August 2, 2009
Let's just say I'm trying to avoid the situation in the picture above. There was a hiccup in my build and as of yet, I'm not exactly certain what the cause was, but I have my suspicions. I was looking at the kayak and the epoxy bond joints between the port side stringers showed some strange marks - like stretching. I poked at the joints and they were a bit soft. The rest of the bond joints were checked and they were very hard, as they should be.
I decided that I'd be safe and remove the "gummy" joints. A sharp utility knife made quick work of separating the chine and sheer stringers from the forms. A sharp chisel then removed the remaining adhesive from the stringers and the frames to provide a good bonding surface with bare wood. A new batch of epoxy was mixed up and the repair was made.
To be honest, the only thing that could have happened would have been a mixing error on my part. The most likely errors would be either poor mix ratio or poor mixing (i.e. not complete). Temperature was definitely not an issue - it was in the mid 80's temperature-wise. The bond surfaces were new, dry and clean wood that has no contamination.
The adhesive in question is System Three's Silver Tip GelMagic pre-thickened epoxy adhesive system. I've been mixing the epoxy by weight on a digital scale - 10 grams of thickened epoxy to 4 grams of hardener. (It can be mixed either 2:1 by volume or 100:41 by weight, hence the 10:4 gram ratio) I have a rule when mixing epoxy - mix for at least 30 seconds before using, so I figure it was thoroughly mixed. The other consideration is that the GelMagic has a blue-tinted epoxy that shows a uniform color when properly mixed. The only thing I can think of was that I must have hit the scale when tareing out the weight of the cup.
Just remember - it is important to figure things like this out. You should learn from your mistakes, not repeat them. Better yet, learn from someone else's mistakes. As a friend of mine likes to say, if you're not making mistakes you can't be doing much.