: I epoxied my plywoood scarf joints 2 nights ago and the epoxy that was
: forced out of the joint has gone sort of rubbery . I contacted the shop
: where I bought my epoxy he said that I probably didn't mix a big enough
: batch to make it kick off ,

A large mass will react faster than a small mass because the large mass will generate more of its own heat. Heat speeds up the reaction, whether generated by the reaction itself or supplied externally, such as with a heat gun. Any given quantity of epoxy will react faster in a small container than when spread thinly over a large surface area, because the thin layer will give its heat off to the base material, the air, and the workbench. If the epoxy is measured and mixed properly, the temperature affects how long the reaction will take, but not the ultimate strength of the material. If you put it mixed in the freezer, and take it out a year later, it will still be mostly unreacted. Warm it up though, and it will continue to cure. There is no evaporation component such as in paint, it is purely a temperature-dependent chemical reaction. That said, there simply is no way that your batch was too small to cure. Two molecules of resin mixed with one molecule of hardener will cure. More detective work is necessary here.

: I'm using aqua set epoxy from fiber-tech in
: Vancouver, he said to pull the joints apart and put a fresh batch on over
: the old stuff and re-clamp .

Wow, this may be the worst epoxy advice I have ever heard!!! If the mix was properly metered and mixed, in time it will harden. Disturbing the bond line during this process can only be a Bad Thing. If the metering or mixing were significantly off, the batch is worthless. In the chain of components in this joint, the bad epoxy would be the weakest link, the spot prone to failure. Fresh, good epoxy applied over the surface of the bad epoxy won't fix it. Fortunately there is some tolerance for error in measurement. Some manufacturers allow 5%, some allow 10%, some allow 5% on hardener but 10% on resin, and others are all over the map. What usually happens in cases like this is a a gross mistake, like using 1:1 instead of 2:1, or 1:2 instead of 2:1. There is a fix for this, but we'll get to that later.

: My problem is that I tried to pull the joints
: apart but it won't come apart, I just put some fresh epoxy over the seams.
: I'm sure the new stuff will set up but I couldnt get between the scarfs,
: does anyone know if given time the stuff between the joints will set?

It may be a good sign that you can't pull the joint apart. If the metering and mixing was correct, it will all gel over time. If not, all bets are off. In cold conditions, the cure is retarded, and partially cured epoxy is rubbery as you describe. However, incorrect metering with too much resin also yields a rubbery end product, which will be weaker than it ought to be. Try heating the whole joint up to accelerate the cure. A 100-watt light bulb left on under the bench will provide enough heat to help, or a space heater will work too, but be careful not to burn the place down.

It is unfortunate that the good new material is on top of the suspect old stuff. That makes testing difficult. But the quick-and-dirty thumbnail test should work if the new stuff is thin. Press your thumbnail perpendicular to the surface, and see whether it leaves a mark in the epoxy. If so, it isn't hard enough. That may be due either to the low temperature or to a resin-rich mixture. Test it again daily, and see whether there is any change. Do this for 4 or 5 days with the heat going 24 hours a day before taking any other action. If it gets to the point that your nail bends before leaving an impression, it will be fine.

Otherwise you will have to fall back to Plan B. It won't be necessary to remove 2 or 3 inches though. A reinforcing plate of the same thickness of marine plywood could be sistered in to straddle the joint on the inside of the boat, and epoxied in place. If you do this before bending the panels into place there will be a lumpy spot in the curve there though, so wait to install it until the panels are bent and wired into shape. This plate should be the full width of the joint and maybe 4 inches on each side of it, for a total of 8" or so. This reinforcing plate will actually be stronger than a correctly glued scarf, so there will be no sacrifice of strength in that area. A fillet of thickened epoxy should be applied around the plate to ease the transition so the fiberglass cloth will conform properly. That part on the inside of the boat is usually hidden by hip pads and such, so appearance won't be much of an issue inside the boat. On the outside of the boat there will be no evidence of repairs at all.

: I'd
: really hate to cut all the joints and then re-scarf and glue making my
: kayak 2 or 3 inches shorter than it's supposed to be . I plan on glassing
: both sides of the hull . Will the scarfs be a weak spot that I'll have to
: worry about ? The leftover epoxy in my mixing cup isn't sticky to the
: touch just kinda rubbery , some chemical reaction must have started the
: garage is around 13C not overly cold . Thanks again for the advice .

Let's see, 13C is about 55 American degrees. Epoxy is tested in the laboratory at 77*F. For the narrow range of ambient temperatures between about 40*F and 120*F, there is a direct relation between temperature change and reaction time. For every 17*F higher than 77, the reaction time is cut in half. For every 17*F lower the reaction time doubles. The difference in temp then is about 22*F, so all other things being equal your batch should take more than twice as long to gel as the factory data sheet numbers would show. The relation breaks down at both ends, since the reaction becomes very much slower at 40*F and comes to a standstill around freezing. If your shop temp drops at night the gel time could be large multiples of the laboratory number.

But remember that all other things might not be equal, as in mixing and metering. Time and your thumbnail will tell.

Incidentally, the best ratio for resin and hardener is whatever the manufacturer says. Adding more hardener won't make it stronger, just brittle and weak. More resin makes it more flexible and weak. The operative word both ways is "weak". Measure it out carefully, stir for a full 2 minutes, and scrape the sides of the cup and the stir stick several times during the process. Most epoxy problems relate to metering and mixing, and are therefore preventable.

Don't get discouraged, there is a way out of this without major surgery on the boat. The folks on this BBS have collectively made every possible epoxy mistake and lived to tell about it. Stop by in a few days and let us know how things went, OK?