The Epoxy Files — Technical Resources


Temperature: The Ultimate Variable 0

If you've used epoxy before, you probably know that mixed resin and hardener can get hot in a hurry. Case in point: Figure 1 - that cup has seen its last day.

This mixed epoxy, along with its 221 °F reading, is the aftermath of what is known as an exothermic reaction. To put it in plain terms: an exothermic reaction is a freight train of heat that sends your mixed epoxy into oblivion. But how does this happen and how can it be prevented?

Figure 1: Exothermically reacted epoxy with temperature for reference.

The driving variable that affects the curing time of epoxy products is temperature. All of the information relating to cure and set times on our product labels is based on a standard temperature of 77 °F (25 °C). Assuming your local environment will be hotter or cooler than 77 °F, a great rule of thumb to keep in mind is that for every additional 18 °F (10 °C) above 77 °F, your cure time will be cut in half. Conversely, for every 18 °F cooler, be prepared for your cure time to double.

The byproduct of an epoxy curing reaction is heat. The fewer opportunities this heat has to escape, the faster this reaction will occur. Looking back at Figure 1 - and thinking about our rule of 18 °F - if the temperature of your mixed epoxy has risen 18 °F after 5 minutes in a cup, its cure time will be halved. Two and a half minutes later, and another 18 °F, now your cure time is halved again. This doesn't have to go on for very long before your cup is smoking, possibly melting, and you're left wondering what the heck happened!

Rotfix, one of the products in our EndRot line, is a great example of how heat effects epoxy. While we do offer a helpful mixing bottle with our 24 Oz. kit, folks often get themselves in trouble by mixing too much product in the bottle and leaving it for several minutes before getting down to work. By the time they are ready to begin, the product has reacted and become very hot! We strongly suggest starting with small, graduated medical cups for RotFix applications since a little product goes a long way, and gets hot fairly fast. This also helps users become more familiar with how our products function.

Preventing exothermic reaction comes down to three things:

  1. Organization
  2. Surface Preparation
  3. Execution

1. Organization

Figure 2: Measuring, mixing and application tools you may need.

Preparing for your project before jumping in will really make a big difference! If you're laminating fiberglass or carbon fiber, this means getting your fabrics cut to size and staged, and then calculating a rough estimate of how much resin you will need (this will come with experience and time using the products). You'll also need measuring, mixing and application tools, like those seen in Figure 2. Getting organized before starting your project will mean spending less time finding your tools and more time getting the epoxy mixed and applied.

2. Surface Area

Figure 3: Great (and inexpensive!) tray to use for expanding surface area.

As discussed in our intro, the reason that mixed epoxy gets so hot in a cup is that the heat being generated has nowhere to go. Preventing exothermic reaction, depending on the application, is usually as easy as pouring the mixture out into a pan. This spreads the epoxy out, thereby increasing its surface area, and allows the mixture to release heat. As seen in Figure 3, paint trays and other disposable baking pans (consider going to your local Dollar Store for these) are great for giving your epoxy, and you, a chance to breathe during the application process.

3. Execution

When applying epoxy, don't jump into a project that you aren't comfortable doing. It's all about starting small and then working up to bigger jobs as you gain more familiarity with the product. Mixing small batches, or however much can be used in a reasonable amount of time, is still something that we continue to do even though we have been using this stuff for many years. It will allow for the flexibility of working with multiple products when your project demands it, you'll eliminate wasted material and save money, and you also won't burn your hand!

We hope this post has helped to clarify how heat affects your epoxy projects. For more information, check out our video below on exothermic reaction:

Repair of the Sloop Kaitin from the Outside In 1

With an undulating impact and subsequent rise and fall of the hull into and out of sight in the rear view mirror, two thoughts flashed to mind: the sloop Kaitlin was not to sail at the 38th Annual Port Townsend Wooden Boat Festival, and that a wooden boat is infinitely repairable. The worst case scenario of boat trailering had just occurred, a rear‐end car collision into a stopped trailered boat. The car's impact and continuing movement forward had, among other events, forced the small transom mounted outboard inward toward and under the hull, explosively rupturing the epoxy laminated plywood transom, leaving both the mount and attached outboard motor separated and hanging on a remaining splinter of wood. Where the motor mount had once been attached was now a jagged edged rectangular hole large enough to pass a soccer ball through.

Why Use Cartridges? 0

T-88 CartridgeWouldn’t it be nice if there were a way to eliminate the chance of measuring and mixing errors, maximize the resin strength by eliminating air, always use freshly mixed material, enjoy top of the line products, save time, eliminate waste and have more fun? There is such a way. It’s called using dual cartridges. To use one you simply drop it into a caulking gun, prime it and screw on the tip to dispense thoroughly mixed and precisely measured material free of air. You put the mixed material right where it is needed with little waste. Using dual cartridges is fun and is the quick, confident way to kick back and watch things cure!

Epoxy Paste Pigments 2

Our  Epoxy Paste Pigments are pure, dry, colored, pigments dispersed in in an epoxy resin blend.  They are pourable, easily measured, and contain no solvents, and may be blended with one another to produce additional colors.  Since they are dispersed in an epoxy resin blend, they react into the system and do not change its cured properties.  The proper way to use these pigments is to add them to the resin (Part A) side and then add the hardener(Part B)  at the correct ratio for the epoxy system being used.

High-performance Coatings for "Do-It-Yourselfers" 0

Over the last thirty years, chemical product manufacturers have had to meet tremendous challenges. Two of these with huge impact are regulatory requirements and, less prominent, but with greater long-term effects, changing customer attitudes. System Three Resins, a manufacturer of polymer products in the marine industry for over twenty-five of those thirty years, has met those challenges. And one area where we feel we've done better than most is marine coatings.

Product Compatibility Questions 0

A common technical question goes something like this: "Will XYZ paint work over your epoxy?" Or perhaps the corollary question "Will your epoxy work over ABC stain?" Our answer, which is almost always the same, often shocks the inquirer: "We don't know, you'll have to test it yourself. Here's how to do it...".

u-TAH Cartridges 0

Simplicity in epoxy adhesive use has finally arrived! Just drop a System Three u-TAH™ cartridge into a conventional caulking gun, add a mixer tip and squeeze and apply. What could be easier?

Postcuring 2

A high Tg resin may be cured in two ways: It can be cured initially at elevated temperatures or it can be partially cured (becomes solid) at room temperature and then heated (post-cured). The two routes get one to the same place if sufficient time is allowed for both. The first route can be tricky because the epoxy reaction is exothermic and may excessively spike the temperature. Most boats are laid up at room temperature - hand lay up, vacuum bagged or infused - and post cured later simply because this route is considerably easier...

Fiberglassing Square Edges 0

Occasionally one needs to bring fiberglass cloth around a sharp edge. This could occur on the trailing edge of a rudder, for example. Those who have tried this know that it is almost impossible to do. The fiberglass is just too "springy" and lifts from the edge creating air pockets. These eventually tear or fill with water. In either case the wooden substrate gets wet and the reason for having the fiberglass there in the first place is lost. While it is possible to keep pushing the fiberglass back down until the tackiness of the resin finally holds it in place there are far better ways to do this.