Epoxy Resin Crystallization

BUILDERA
Frequently-Asked Questions
FQ2018-1

Revision 1.2 February 09, 2020

Background

Two-part epoxies may exhibit non-permanent, reversible crystallization when exposed to cold temperatures or temperature cycling during transit and storage. Crystallized epoxy resin becomes partly to fully solid, making it difficult to dispense with reasonable plunger pressure. As a convenience to our commercial and consumer customers, BUILDERA offers premium, industrial two-part thixotropic epoxy adhesives (STRUPOXY®) to securely install structural crack monitors and for other general-purpose bonding use. This Frequently-Asked Questions (“FAQ”) answers common concerns to help users understand:

• Causes of epoxy crystallization;

• Best practices for proper storage and crystallization prevention, and;

• How to prepare and recondition crystallized epoxy for use on the job site.

Q1. What is epoxy crystallization and what causes it?

Crystallization causes in-situ material firming inside the epoxy syringe or storage container, which typically affects epoxy resins (“Part A”) of two-part epoxies. The catalyst or hardener (“Part B”) is less likely to crystallize. Exposing uncured epoxy adhesives to cold tempe­ratures, temperature cycling, and/or transportation shock, may cause crystallization to occur spontaneously—without warning. Exposing the epoxy vessel to mild heat will fully thaw the resin to factory conditions.

Just as water crystallizes and hardens upon freezing, epoxy can also change state from a liquid, gel or paste, into a solid at slightly cool temperatures—with increasing risk when stored below room temperature. Once the epoxy has crystallized, even when warmed back up to room temperature, crystallization may persist until all of the crystals are re-melted at a higher temperature.

Crystallization does not damage the epoxy, but it may be difficult to dispense. Depending on the extent of crystallization, you may rejuvenate mildly crystallized epoxy in a few minutes by exposing the syringe tip, barrel, and its contents to a gentle warming with a hair dryer. In more extreme cases where the entire contents have crystallized, warm the epoxy in a water bath or convection oven for three hours at 120 ºF (49 ºC) or two hours at 140 ºF (60ºC), or until all physical and visual signs of crystallization have vanished.

Q2. How do I know whether the epoxy has crystallized?

The short answer is that you don’t know for certain whether the epoxy has crystallized until you try dispensing it. However, there are some helpful clues. For example, for thin free-flowing liquid epoxies that are normally clear and transparent, crystallization may appear as a cloudy or milky-white color at room temperature. This may be an indication that the epoxy should not be used until soft heat is applied to melt the crystals. However, BUILDERA STRUPOXY—and most thixotropic epoxies—are engineered to be a thick paste or gel at room temperature—similar to the consistency of petroleum jelly or Vaseline®. The natural color is typically translucent to whitish, and this is normal. Therefore, visual inspection of epoxy color or transparency is not a reliable test to determine whether thixotropic epoxy has crystallized.

One subjective (albeit unscientific) method is to firmly compress the middle portion of the translucent epoxy syringe between your thumb and forefinger. If at room temperature (or above) the epoxy tube is extremely difficult to compress, this may indicate partial or full crystallization. Conversely, if the epoxy tube feels slightly pliable or compressible, crystallization is less likely. In either case, the best approach is to pre-warm and fully acclimatize the epoxy above room temperature just prior to use. If the epoxy still remains difficult or impossible to dispense, full epoxy crystallization is likely. Always be sure to remove and set aside the attached black plastic cap between the plunger barrels, as this will interfere with plunger depression if it remains in place prior to dispensing the epoxy.

Q3. How do I avoid epoxy-resin crystallization?

Crystallization is challenging to fully prevent because the manufacturer, distributor, and end-user have no control over temperature cycling during transportation between the point of manufacture and end-use. Although crystallization can be more common during shipment in colder months, it can still occur throughout the year if the conditions are right. Users of epoxy should understand the reasons for crystallization, and that this is a natural phenomenon typically beyond manufacturer or consumer control. That said, proper storage is key to mitigating the likelihood that epoxy will crystallize prior to use (assuming it did not already crystallize during shipment). Storage and usage recommendations include:

• Avoid storing epoxy in a vehicle, unconditioned basement, garage or outdoor shed. Temperatures in these locations fluctuate widely throughout the day and season, and may catalyze the crystallization process.

• Store epoxy in a dark, dry location with a year-round temperature range of 68-80 ºF (20-27ºC) and avoid wide temperature variations. Cold temperatures or wide fluctuations of just 20-30 degrees Fahrenheit can catalyze the crystallization process.

• Avoid vibration or shaking that can stimulate crystal seeds to form and multiply.

• Do not contaminate the epoxy between uses. Foreign matter in the epoxy can create seeds (building blocks) for crystallization.

• Gently warm the epoxy prior to use, following manufacturer procedures. This helps to reduce viscosity allowing it to flow more freely.

Q4. Why did my epoxy crystallize even though I stored it at the recommended temperature?

Crystallization may have occurred during shipment or at the delivery point, such as inside a package left near the front door, mailbox or unconditioned garage. Subsequently storing the epoxy at room temperature is insufficient to reverse the crystallization if it has already occurred. If your home or office has a setback thermostat (most do), temperatures during the night or day may still fall well below room temperature—enough to stimulate crystallization. The epoxy may have also started the crystallization process during shipment where packages can be exposed to highly variable temperatures beyond the control of the manufacturer, the reseller, or end-user.

Q5. I’m on the job site and I can’t dispense the epoxy. Now what?

We understand that it’s frustrating to be on the job and run into obstacles. Fortunately, there are several possible remedies depending on what resources you have on site.

Before anything else, always try to warm the epoxy thoroughly to above room temperature. This will help to restore the epoxy to its original condition and reduce its viscosity, making it easier to dispense. This can take a while if the epoxy is cold, or has been previously exposed to cold temperatures and has already fully crystallized. Sources of heat may include but are not limited to:

• Heat gun

• Hair dryer

• Propane lighter (take caution!)

• Hot or warm water

• Heated jacket

• Automobile or truck heater

• Other accessible appliance (such as a toaster oven or convection oven). Do not overheat the epoxy or syringe. Apply external heat with a gentle sweeping motion across the tube body, particularly near the narrow tip, which can become clogged.

• As an alternative to epoxy, use an all-purpose outdoor-grade construction adhesive compatible with plastics (acrylic, polycarbonate) and concrete. BUILDERA cannot guarantee that a given adhesive will bond and hold properly, so it’s a good idea to test first with a full cure.

• In a pinch, or in rainy weather, fasten the crack monitor mechanically using #8 1-1/2”-long fasteners such as hex sheet-metal screws and plastic anchors instead of—or in conjunction with—all-weather epoxy.

Q6. What does thixotropic mean, and why should I specify it when selecting epoxy?

Thixotropic epoxy is a viscous, non-sagging formulation engineered to mix and spread easily but resist dripping. Unlike free-flowing liquid epoxies, thixotropic epoxies are very thick at room temperature, similar to pastes or gels with a Vaseline®-like consistency. Thixotropic epoxies excel in applications that must cure quickly while avoiding drips and runs. Installing items on a vertical surface or ceiling are situations where thixotropic epoxies work best. Concrete crack monitors are a good use-case for thixotropic epoxy requiring excellent adhesion, no sagging, and fast-curing performance. Although some thixotropic epoxies are also fast curing, not all fast-curing epoxies are thixotropic.

The related term—viscosity—is a technical measure of fluidity of a substance, or resistance to gradual deformation by stress. According to CSC Scientific, “viscosity is the measure of a substance’s resistance to motion under an applied force. The result is typically expressed in centipoise (cP), which is the equivalent of 1 mPa-s (millipascal-second). Shear stress is the force per unit area required to move one layer of fluid in relation to another.”

For example, water (at room temperature) has a reference viscosity of 1 cP, whereas peanut butter has a viscosity of 150,000 cP to 250,000 cP. Some thixotropic epoxies have even higher viscosities that are difficult to measure prior to mixing. Moreover, the viscosity of a material changes with temperature. Warming epoxy prior to use typically lowers its viscosity to improve flow. This reduces the force required to dispense the epoxy.

Q7. What does Part A and Part B mean?

Two-part epoxies include an epoxy resin (Part A) and hardener or catalyst (Part B). Upon mixing the two parts in specified proportions (often 1:1 by volume), a heat-producing (“exothermic”) chemical reaction starts the curing process. Mixing even a small portion of epoxy, such as 30 ml (1 ounce) can result in rapid heat generation capable of severe skin burns. For this reason, always mix epoxy in open air and in small batches—just enough for the current use.

Q8. If my epoxy has crystallized, should I return it or just throw it away?

Neither. There is generally no technical reason to return or discard crystallized epoxy. Crystallized epoxy is still perfectly usable so long as you remelt the crystals following the manufacturer’s procedure. Moreover, avoid discarding uncured epoxy resin or adhesives, as these contain chemical formulations that could leach into the ground or harm the environment. It’s always best to naturally reverse the crystallization before deciding to discard or replace it. If you do elect to discard the epoxy or a partially used tube, wrap and seal it in a heavy-duty plastic bag with a rubber band. This will help to prevent accidental discharge during storage or disposal. Adhere to all local regulations for proper disposal. If you have any support questions or require technical product assistance, please contact BUILDERA customer service at https://www.buildera.com/ask

Q9. What precautions does BUILDERA take to help prevent epoxy crystallization prior to shipment?

BUILDERA takes several precautions to ensure that all epoxy leaves our warehouse in its purest form. These include:

• Storing all epoxy in a climate-controlled facility with a year-round temperature fluctuation of ±5 ºF. We monitor temperature and humidity using a commercial data logger to ensure proper storage.

• To ensure our customers the best possible experience, and as part of our commitment to continuous improvement, we process every tube of epoxy prior to shipment using a precision-controlled laboratory temperature chamber. Every tube of epoxy leaving our premises is in new condition and has not crystallized due to storage in our own warehouse.

• For every batch of epoxy, we archive several samples for later testing at periodic intervals. Some of our tests are now on epoxies that are three or more years old. When testing the epoxy based on date codes, we can measure and compare its heating (curing) performance in a 30 ml test cylinder using a precision thermocouple and laboratory instrumentation. This gives us confidence that older epoxy is still perfectly usable even after it has surpassed its recommended shelf life.

• In addition to heating tests, BUILDERA may also test the epoxy hardness using a Shore-D durometer which indicates whether the epoxy has achieved its expected hardness after a 24-hour cure. These tests give high confidence that the epoxy is curing properly.

Summary

Epoxy crystallization is a natural phenomenon that causes the epoxy resin to harden in its carrier due to exposure to cold temperatures or thermal shock. Crystallization is fully reversible through mild heating which melts the crystals and restores the epoxy to like-new factory conditions.

REVISION HISTORY

Revision 1.2 (February 09, 2020)

• Added online (web) version with link to downloadable PDF

• Minor updates to viscosity table and change to 120 ºF (49 ºC) for minimum restoration temperature

Revision 1.1 ( April 25, 2019)

• Final release (PDF version)

Revision 1.0 ( March 31, 2018)

• Initial draft

How to reference this document

BUILDERA. “FAQ FQ2018-1 Epoxy Resin Crystallization.” Version 1.2. Feb. 09, 2020. https://www.buildera.com/faq-fq2018-1-epoxy-resin-crystallization

References

[1] https://www.epotek.com/site/files/Techtips/pdfs/Tech_Tip_3_-_Viscosity_and_TI.pdf

[2] https://www.permabond.com/2013/05/14/understanding-adhesive-viscosity-rheology/

[3] https://www.vp-scientific.com/Viscosity_Tables.htm