. . . would someone please explain to me the following:

I have read, both in these forums and in numerous rod building books, that if you want to extend the pot life of a batch of mixed wrap finish once mixed, to place it on a flat lid/aluminum foil for it to spread out.

The thing I don't understand is that, normally, if you spread something out and cause more contact with the air, the drying process is usually shortened, not lengthened, ie, a three gallon pail of water sitting outside will take a long time to evaporate, but if you emptied the pail of water onto the driveway, greatly increasing the area of contact to the elements, it would dry up very quickly.

Now, I know that water evaporation is not the same as the hardening of epoxy but, to me anyway, the basic principle would seem to hold true. And, in no way am I suggesting that what I've read is not true and factual.

Inquisitive minds want to know!

Thanks for taking the time to enlighten me. I enjoy not only the "how", but the "why" as well.

(Copied directly from this site's FAQ's: "To extend pot life and help in releasing any bubbles introduced during mixing, pour your epoxy out onto a piece of aluminum foil and work from there.")

Okay, first, epoxy cures by a reaction between the two component parts, not by exposure to air. So spreading it out and exposing more surface to the air won't cause it to set faster.

One thing that does cause epoxy to set faster, is heat. For every 18F rise in temperature above about 70F, you halve the setting and cure time. When you keep an epoxy in a cup, and contain the exothermic heat from the reaction, you greatly increase the temperature of the mix and thus reduce the setting and cure time.



..................

Ralph,
Mixing the two parts of epoxy creates an exothermeic reaction. That is, the mixtures heats up due to the chemical reaction. Heat causes epoxy to harden quicker. By putting the mixture on a flat sheet of aluminum foil, you allow the mixture to spread out and quickly dissapate the heat of the reaction into the aluminum foil which is an excellent heat conductor. I actually cover a large metal lid with the aluminum foil and place it in the refrigerator or freezer for about 1/2 hr. before mixing the epoxy and can get up to 45 minutes of working time on a batch.

Epoxy finish is a cemical reaction when mixed and will harden much faster in a contained space such as a one ounce mixing cup than when spread out in an 8 inch aluminum pie pan. This is what I use on just about a daily basis. Working out of the pie pan I can get up to a half hour working time by reheating the epoxy with the prophane torch where I've seen the stuff become to thick to use after sitting only 5 min. in the one ounce cup. Jesse

Exothermic reaction, great - I understand it now! Thank you. BUT -

Tom, you said "One thing that does cause epoxy to set faster, is heat." And Jesse said ". . . I can get up to a half hour working time by reheating the epoxy with the prophane torch . . ."!

If heat causes the epoxy to set, how can you extend working time by applying more heat?

Do to the exothermic reaction when the 2 chemicals are mix, the cure time is increased when the mixture is left in a mixing container. Thus to slow down the cure time I use foil; thus the heat is transferred to the foil and not to the mixture. I got this hint from Flex Coat a few years ago. Add 3 drops of Acetone to a one oz mixing container while mixing the 2 parts while slow down the cure time and break up the micro bubbles. the down side it increases the cure time on the rod 2 fold. If the finish is on a rod that is turning and starting to set up and is sticky. An I spot a problem. I use a Propane torch to re liquify the finish and correct the problem
Good Wraps Bob

When I heat the epoxy it thins out for a very short period of time and thickens much faster than regular cure time. About 3 re-heats is about all I can get before the stuff really gels up to thick to use. Jesse

When you apply heat to an epoxy it will momentarily thin it, just few a handful of seconds. When it returns to where it was before, of course, it's now even warmer and setting even faster. And, there is a only a short window where this is possible. At some point as it begins to set, adding heat will have little effect on thinning it, only setting it even faster.

......................

OK - I'm "Cured" ; )

Heat is part of the curing process. Applying heat during the curing stage will lengthen pot life to a point, but it is only a very temporary, short-lived fix.

I really do appreciate everyone's response. Thank you!

Not quite - heat always speeds the cure; reduces your pot life. Always.

High heat will momentarily thin the epoxy, but it will still reduce the pot life.

............

If you really want to increase "pot life" the easiest way is to dilute the reactants. I have used denatured alcohol. It does not take much to slow it down. You can make it last for 24 hours if you wish. Another way is to reduce the amout of hardener by 5% or so. I don't really want to get into the details of the kinetics of a first order reaction, but those trained in the art do understand what I am talking about. Heat does accelarate this reaction. For every 10 degress C you increase the temperature you double the reaction rate (approximately). Bottom line: You are better off not messing with the instructions. Measure both components accurately and make up a minimum of 5 cc's. You should have ample time to completely finish an entire rod. (<15 ft.)

Ed Smith

When I apply heat to finish that is all rady on a wrap and the wrap it turning the excess finish will glob on the bottom side and I remove th glob to have a thiner finish on the wrap . this also gets rid of the foot ball effect of having to much finish on the wrap and also alows the finish to penitrate to the blank on wraps that do not have a color preseriver added to the thread.
Good Wraps Bob