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It's been 90+ degrees here and my epoxy is way too fast.  I'm going to order some slow hardener but am waiting to get the funds to order it and my cloth together.  Has anybody ever tried putting the epoxy in ice to cool it off before mixing.  I thought it might give me an extra 5 minutes before it started cooking off.  It works for beer.  If nobody knows I'll try it and let you know.

Putting your pot of epoxy in a bucket of ice water does help to some degree, but I use a different method.

Most folks mix their goo in a small plastic container, then apply the goo from there. This permits the epoxy to heat up because it's massed in the mixing cup.

After mixing my epoxy, I immediately spread it out on a piece of plastic or plywood (pre coated of course) to a very thin layer of goo.

In fact, I do the majority of mixing in fillers directly on this same board. I also have some large plastic trays that I use, if it's a runny mixture.

Spread out into a very thin sheet of goo, it's easy to pick up with a plastic applicator or putty knife, but more importantly it doesn't heat up nearly as fast, because it's not massed in a lump at the bottom of a mixing cup. This can double the working time you have.

I use epoxy in mid 90 degree weather all the time and have learned this is the best way. Cooling down the epoxy decreases viscosity which can make a fillet that appears perfect when first applied, sag like a 50 year old's boobs, after it warms up on the work. I've had this happen and there's little you can do short of making a temporary dam to hold back the sagging mess.

Also store you epoxy indoors, where it's in the low 70's most of the time. Mix in doors if you can and spread it out paper thin.

My usually 6 ounce mixing board is about 2 square feet of space to spread out the goo. I have bigger boards for bigger batches.

Another nice thing about this method is you don't have to scrape the sides of a container, which can be a pain in the butt some times.

What a great idea, Thanks Paul that will help me out a bunch.

Greetings Paul,

So the next question would be, which brand of epoxy do you use in 90 degree weather and specifically which hardener?

The whole picture for successfully applying epoxy is a combination of materials (exactly which hardener and resin), technique (spreading the goo out on a tray to increase its pot life), preparation (having everything dry fit perfectly and lined up for quick assembly), and help (extra hands who have been instructed in or know what to do).

I have some previous experience in fiber glassing small structures for radio controlled airplanes.  Some of the wing panels we build are cut from foam cores using a hot wire knife, covered in balsa wood, and sheathed in fiberglass. With the wing tips set on two chairs, the resulting structure is strong enough to support my 206 lbs. That kind of strength is required in pylon racing where the speeds exceed 140 mph and a 15G turn will make that 5 lb airplane appear to weigh 75 lbs.  Without the fiberglass, the plane explodes like confetti.  But I digress.

Unfortunately, my previous experience was also a handicap in that the resin and hardener combinations sold at the hobby stores are formulated to provide short cure times in the average basement (65-70 degrees).  If you were glassing a large wing, you had to move quickly to get it all done before the goop started to glob up on you.  And the penalty for mistakes was severe – cut new foam core, glue on more balsa, and try glassing again.  You could not just scrape it off and sand down the imperfections because the wing had to be perfectly symmetrical in shape and balanced in weight or the plane behaved badly at speed.

This learned fear of going back to square one after a mistake led me to use the Weldwood Plastic Resin glue on the Weekender, as it has a ridiculously long 2 to 4 hour pot life (depending on temperature) and a 20 to 30 minute joint life.  In practical terms, I can be the lazy sloppy mistake-prone novice boat builder that I am and the glue is ok with that.

Since I started construction of my Weekender, I have learned that there are more epoxy resins and hardeners available than what is sold in the hobby store and there are professional techniques you can use to adjust the working time of the goo.

The West Systems web site has a nice product selection guide at http://www.westsystem.com/ss/product-selection-chart which includes a nice picture showing all of their hardeners and additives and what they might be useful for.  At http://www.westsystem.com/ss/hardener-selection-guide/ there is a nice chart showing the pot life of the epoxy when the various hardeners are used.  The table shows pot-life times at 70 degrees.  So adjusting for the heat and the slow clumsy efforts of the novice boat builder, it looks like the 209 Extra Slow Hardener would be the right stuff to use.

While the West System web site does have a lot of good information, you have to read a lot to find what you are looking for.  For example, on Page 61 of the free Wooden Boat Restoration and Repair guide ... http://209.20.76.247/ss/assets/howto-pub...Repair.pdf, they describe the curing process thusly …

Hardener Speed

Each hardener has an ideal temperature range (figure 8-1). At any given temperature, each resin/hardener combination will go through the same cure stages, but at different rates. Select the hardener that gives you adequate working time for the job you are doing at the temperature and conditions you are working under. The product guide and container labels describe hardener pot life and cure times.

Pot life is a term used to compare the cure speeds of different hardeners. It is the amount of time a specific mass of mixed resin and hardener remains liquid at a specific temperature.  (A 100g-mass mixture in a standard container, at 72ºF). Because pot life is a measure of the cure speed of a specific mass (volume) of epoxy rather than a thin film, a hardener’s pot life is much shorter than its open time.

Epoxy Temperature

The warmer the temperature of curing epoxy, the faster it cures (Figure 8-3). Curing epoxy’s temperature is determined by the ambient temperature plus the exothermic heat generated by its cure.

Ambient temperature is the temperature of the air or material in contact with the epoxy. Air temperature is most often the ambient temperature unless the epoxy is applied to a surface with a different temperature. Generally, epoxy cures faster when the air temperature is warmer.

Exothermic heat is produced by the chemical reaction the cures epoxy.  The amount of heat produced depends on the thickness or exposed surface area of the mixed epoxy. In a thicker mass, more heat is retained, causing a faster reaction and more heat.  The mixing container shape and mixed quantity have a great effect on this exothermic reaction. A contained mass of curing epoxy (8 fl oz or more) in a plastic mixing cup can quickly generate enough heat to melt the cup and burn your skin. However, if the same quantity is spread into a thin layer, exothermic heat is dissipated, and the epoxy’s cure time is determined by the ambient air temperature.  The thinner the layer of curing epoxy, the less it is effected by exothermic heat, and the slower it cures.


Wow, isn’t that nice.

What we amateur boat builders need is simple instructions.

Example: When it is sweating hot outside …Put on nitrile gloves and old clothes. Use West 105 resin and 209 hardener. Mix the goop on a cookie sheet or cafeteria tray to keep the mixture thin so it doesn’t go off to quickly.  Spread quickly using an el-cheapo plastic spatula/scraper.  Enjoy a beer when done.  The beer at the end is important as it will keep you focused and working quickly … so that you can get to the beer.

Those are the kind of instructions most of us need.

Cheers,
Tom.

I use the same method as Paul to keep epoxy "soft" when the job is bigger then a quick patch.

I use a proprietary mixture I call my super slow. It's from a local formulator. Now that I've learned how this particular chemistry works, I can modify "unrefined" resins to get the physical qualities I desire. Going to the U of D as a chemE major helped quite a bit.

My super slow (which is labeled Paul's mix by the formulator) will offer 55+ minutes in the low 90's and 40 minutes in the upper 90's. This stuff just will not kick if the temperatures is in the low 70's (okay maybe in a month).

West System 209/105 will offer about 40 minutes in the low 90's, but in the upper 90's it's reaching it's limit and can kick off fairly quickly, especially if permitted to pool.

BoatBuilder Supply (Bateau.com) has a good 2:1 slightly refined epoxy. Their slow hardener will be almost as good as 209 (slightly quicker) but at a substantial savings. If you elect to get some, tell Joel, PAR sent you and maybe he'll give you a pro builder's discount. It's a blush free mix, unless you apply it in the rain (been there, done that) and has good viscosity control and wetout ability.

I dislike Raka, finding it's too thin and requires more coats to do the same job as others, though the price is good. I couldn't comment about their hardener rates.

I'll assume System Three has a slow, but haven't used any in many years.

You must remember, I'm in  a tropical environment, so special formulations are pretty much required. I'm currently using 5 different types of epoxy.

Thanks Paul, I used the spread thin technique and it really worked great.  It's cooled off here so I'm gonna lay the keel/bottom fillets tonight.  My wife suggested using her disposable pastry bags and it works well.  I'm using the Marine Epoxy from duckworks. Thanks again

The marine epoxy from DuckWorks is the stuff I mentioned (BoatBuilder Supply at Bateau.com). You can save some money by calling Joel directly and have him ship it to you.