: I have just started construction of a Pygmy Artic Tern '14 and I have a
: couple of questions: 1) In my very first batch of epoxy mixed together in
: an effort to glue the butt seams together, I somehow managed to not put
: enough hardener in. It has been over a week and it is still slightly tacky
: spots. Any suggestions for handling this? Or just wait it out until it is
: completely hardened (assuming it will completely harden).

: 2) I did manage to mix appropriate amounts of resin and hardener while
: glueing the other butt seams. I just started sanding the hardened resin
: down to be smooth with the wood. How picky do I need to be about this. I
: have developed some air pockets in the cured epoxy and I am wondering if
: it is necessary to completely smooth these out. OR, will the subsequent
: coats of resin and glass fill these in sufficiently. Any other suggestions
: about working with this very first step??????

Most epoxy problems involve mixing and metering. Measure very carefully to avoid the metering problem. Use small graduated cups and visually verify quantities. It helps to premark pour lines on the side in felt pen, e.g. one at 10 cc and another at 30cc; fill to the first with hardener, and to the second with resin. Note that you won't be able to pour out all the epoxy, and the remainder in the bottom will screw up the measurement of your next batch, so either use a new cup, or leave the stir stick in and use it as a handle to pull out the cured glob when it's time for the next batch. Sidebar: when ratios are off there is usually too much hardener, not too little. Off either way is bad. Optimum physical properties of the cured epoxy require stoichiometric quantities of both resin and hardener.

Mixing is also critical. Manufacturers recommend mixing for 2 minutes with a drill and mixing paddle. That is not feasible for the small quantities that we work with, but it's a good guideline for time. Some guys chuck up screws in drills and use them for mixers, others use scraps of strip. Some other guys mix in the measuring cup, then transfer to a clean cup and continue mixing. An old professional boatbuilder in Wooden Boat a while back recommended stirring 100 strokes, and said that in 40 years he had never experienced a failure. 200 would be even better, there is no downside to overmixing. The resin and hardener of clear epoxy are so close in color that you can't tell by looking whether the mix is good, so your technique has to compensate for lack of visual cues. Make sure you scrape the sides of the cup often, otherwise you will have unmixed areas in the finished product. It sounds as though this may be your problem.

Temperature is also a variable. If your shop is cold it will take longer to cure. But if your metering and mixing is right, eventually it will kick.

If you have any qualms about whether it was done correctly, my recommendation is to remove it and start over. Subsequent layers of good epoxy will not compensate for one layer of bad. Unless all the bond lines are sound, the structure is subject to failure. And that could happen at some very inconvenient time and place...