Epoxy Mystery Solved: A Cautionary Tail
By Roderick Kabel
At WiseBond®, we take immense pride in our customer service. Every email, chat, and phone call is personally answered with care and attention. Over the years, we’ve encountered numerous customer stories—some heartwarming, others challenging—and we’ve always strived to get to the root of their problems, solve mysteries, and provide effective solutions.
This case underscores why we prioritize personalized service and in-depth problem-solving. At WiseBond®, we’re not just here to sell products—we’re here to ensure your projects succeed. Whether it’s troubleshooting, providing advice, or sharing insights, we’re always ready to go the extra mile for our customers.
The Case of the Yellowing Epoxy
Recently, a customer reached out to us with an intriguing issue: their epoxy project had turned yellow – in 3 days after pouring! As always, we began our inquiry by reviewing every pertinent detail—from mixing and pouring techniques to the workshop environment, air temperature, and curing conditions.
The project in question was truly one-of-a-kind: a series of custom stair treads made from stainless steel with “S”-shaped whimsical, deep-pour epoxy cavities, all finished with tabletop epoxy. Each tread had been meticulously handmade and welded from stainless steel.
- Step 1: Deep Pour Epoxy: The customer poured deep-pour epoxy into “S”-shaped cavities on each tread and allowed it to cure. This stage went smoothly.
- Step 2: Tabletop Epoxy Flood Coat: The next step was leveling off the 1/8" deep-pour sections with tabletop epoxy and flooding the entire tread surface.
After completing the pour, the customer closed the shop, leaving it heated to ensure proper curing in the chilly, snow-laden upper Northeast. Three days later, they returned to inspect their work, only to find a startling result: the epoxy had turned yellow over the stainless steel and green over the blue-tinted deep-pour cavities.
A "Bad Batch" of Epoxy?
Initially, the customer—a seasoned epoxy user with eight years of experience—assumed the issue was a defective batch. To test this theory, they mixed a small sample of the same tabletop epoxy and observed it yellowing within hours in their workshop.
Above image of table top epoxy drips from flood coat pour.
Above image of customer test over a white board yellowed within hours.
But at WiseBond®, we’re confident in the quality of our products. We don’t have “bad batches.” So, we dug deeper.
Uncovering the Root Cause
As we analyzed the customer’s photos, one image stood out. It showed a stair tread partially sanded, revealing clear epoxy beneath the yellowed surface. This discovery ruled out a systemic issue with the epoxy itself. The yellowing was a surface phenomenon, pointing to an environmental factor.
We began asking additional questions about the workshop environment:
- Were cleaning agents with high VOCs or solvents used?
- Could animal byproducts from nearby kennels be a factor?
Then, we noticed a propane heater in the background of one of the photos. This detail triggered a breakthrough in our investigation. We’d previously heard reports from floor epoxy installers that propane heaters could cause epoxy to yellow. The pieces of the puzzle finally fell into place.
How Propane Heaters Cause Yellowing
Propane heaters emit carbon dioxide (CO2), trace amounts of carbon monoxide (CO) if ventilation is poor, and nitrogen oxides (NOx), which are known to chemically interact with epoxy surfaces. These emissions can cause yellowing, particularly when epoxy is curing. While the heater kept the workspace warm, its byproducts had an unintended consequence on the epoxy. It is very important to have fresh air circulating over the surface during drying.
Above image of table top epoxy showing the top surface yellowing.
Solving the Mystery?
We understand that in cold climates propane (and natural gas) heaters can be a necessity. We aren’t advising our customers or anyone for that matter not to use propane heaters in their workshops. Our goal is to offer an educational view of a problem we helped a customer solve.
How Propane Heaters Contribute to Epoxy Yellowing
Propane heaters are commonly used to warm work environments during colder months. When burned correctly, propane primarily emits carbon dioxide (CO2), with trace amounts of carbon monoxide (CO) if ventilation is insufficient, and nitrogen oxides (NOx), which are known contributors to smog formation. Additionally, propane combustion produces very low levels of particulate matter and sulfur oxides. While these emissions might seem harmless at first glance, they can have a significant impact on epoxy resin surfaces.
- Nitrogen Oxides (NOx): These trace emissions can react with the components of epoxy resin, particularly when exposed to heat, leading to chemical changes that cause yellowing. NOx is also a reactive compound that can affect the curing process, altering the resin’s color and clarity.
- Carbon Dioxide (CO2): High concentrations of CO2 can create a localized environment where oxidative processes accelerate. This oxidative stress can speed up the breakdown of epoxy’s molecular structure, resulting in discoloration.
- Particulate Matter: While propane heaters produce low levels of particulates, any airborne impurities can settle on uncured or partially cured epoxy, contributing to surface imperfections and discoloration.
Differentiating Yellowing from Epoxy Blush
It is crucial to distinguish between yellowing caused by propane heater emissions and a phenomenon known as “epoxy blush.” Epoxy blush occurs when a high-humidity environment interacts with amines in the resin, forming a cloudy, waxy layer. Yellowing caused by propane heaters, on the other hand, is the result of chemical interactions with emissions and is permanent unless addressed by sanding and recoating.
Safety Implications of Using Propane Heaters
If a propane heater’s emissions are significant enough to discolor epoxy resin, the work environment may not be safe for prolonged human occupancy. Inadequate ventilation can lead to a build-up of CO and NOx, posing serious health risks:
- Carbon Monoxide Poisoning: Even trace amounts of CO can accumulate in poorly ventilated spaces, causing headaches, dizziness, and, in severe cases, life-threatening conditions.
- Respiratory Issues: Prolonged exposure to NOx and particulates can irritate the respiratory system, leading to long-term health problems.
To ensure a safe and resin-friendly workspace, always prioritize proper ventilation when using propane heaters. Consider alternative heating options, such as electric space heaters, which do not emit combustion byproducts.
Tips for Avoiding Epoxy Yellowing
- Maintain Proper Ventilation: Ensure that any combustion heater is vented to the outside, reducing the concentration of harmful emissions in the workspace.
- Choose the Right Heater: Opt for electric or infrared heaters that do not produce emissions, minimizing the risk of yellowing and health hazards.
- Monitor Temperature and Humidity: Keep the work area’s temperature and humidity levels stable, as fluctuations can also negatively impact the curing process.
- Use High-Quality Epoxy: Some epoxy formulations are more resistant to environmental factors, including NOx and CO2 exposure.
- Seal the Workspace: Minimize the entry of external pollutants by using air filters and sealing gaps in windows and doors.
Conclusion
The yellowing of epoxy resin caused by propane heaters highlights the importance of understanding the interplay between environmental factors and material properties. Beyond aesthetics, this issue serves as a reminder to prioritize safe working conditions. By making informed choices about heating and ventilation, you can protect both the quality of your epoxy projects and the health of everyone in the workspace.
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