Troubleshooting Epoxies

Resin Designs creates and designs custom epoxies for a variety of industries. These products provide superior adhesion to metals, ceramics, rubbers, glass and plastics. Below are several issues face when working with epoxies, as well as some tips on how to fix them.

Issue #1: The epoxy mixture has not cured once the cured time has passed.

Origin of Problem #1: Improper ratio of hardener to resin: The first step is to remove the uncured epoxy. Do not try to apply additional material over the epoxy. Make sure you are using the proper number of pump strokes and avoid using extra hardener for a faster cure. Extra hardener will lead to a different cured properties.

Origin of Problem #2: Low temperature: In colder weather, be sure to allow extra curing time since the reaction will occur slower. Adding heat will allow the chemical reaction to be maintained or even sped up. If your application required low temperature curing make sure to utilize a hardener cures at low temperatures.

Origin of Problem #3: Improper mixing: Again, remove the epoxy in this situation and don’t let new material cover the epoxy. Resin and hardener should be mixed together so there are no resin-rich or hardener-rich areas. If mixing manually a different static mixer might be necessary to allow homogeneous mixing. Diagnosing improper mixing is easy as the epoxy cure properties will not be consistent throughout the whole polymer.

Origin of Problem #4: Wrong products: After removing the epoxy, check for the correct resin and hardener. Hardeners and Resins are not interchangeable unless verified by the manufacturer. The resin won’t cure correctly with polyester catalysts or other brands of hardener.

Origin of Problem #5: Size of adhesive cured:  The speed at which epoxies cure is directly correlated with the mass. If the curing adhesive is lower in mass than the described mass for cure time on a data sheet the gel and cure time will be longer. Some epoxy reactions may even stall if the mass is too small.


Issue #2: The bond has failed.

Origin of Problem #1: Epoxy wicked into porous surfaces, causing a void at the joint: First wet the bonding surface and then apply a thickened epoxy. For the porous surfaces, re-wet these and end grain.

Origin of Problem #2:  Bond surface is contaminated: The surface should be cleaned and sanded, especially wood surfaces.

Origin of Problem #3: Bond area is too small for the load on the joint: Add fillets, bonded fasteners and scarf joints to increase the bonding area.

Origin of Problem #4: Clamping pressure squeezes epoxy out of the joint: Only a small amount of epoxy should be squeezed from the joint.


Issue #3: Epoxy got hot and cured too fast.

Origin of problem #1:  Epoxy mass is too large: For batches of epoxies that are too large, mix smaller patches. The mixture should be transferred to a container with more surface area once mixed.

Origin of problem #2: Applications that are too thick: Create several thin layers for areas that are too thick.


Issue #4: Part A resin hardened and is now white.

Solution: Some epoxy resins (part A) crystalize at room temperature over time. Heat the container to 120 degrees Fahrenheit to melt the crystalized resin.


Issue #5: The Part B Hardener is too dark.

Solution: Due to air (specifically moisture) and sunlight, hardeners tend to darken over time and become more yellow. This does not necessarily mean that the hardener is bad, but a requalification will be necessary.


Issue #6: The epoxy resin is taking too long to cure.

Solution: Once the epoxy resin has been applied, you can heat the room that the project is in.


Issue #7: I don’t know how to clean the cured epoxy resin.

Solution: Cured epoxy systems are quite chemical resistant so they should be removed with an epoxy-type paint stripper. This paint stripper must contain methylene chloride. Epoxy resins and hardeners that are uncured should be cleaned with ketones, lacquer thinner and alcohol.


Issue #8: Materials won’t bond together with epoxy resin adhesives.

Solution: Wood, aluminum and glass bond with epoxy resin adhesives. However, Teflon, polyethylene and polypropylene and nylon will not bond. Materials that are not similar bond well together with epoxy adhesives.


Issue #9: The formation of bubbles on the cured epoxy.

Solution: Cover the bubbles with peel-ply, release fabric or thick plastic. Bubbles typically form from epoxies curing too quickly. Try to cure at low temperatures or use a low temperature curing epoxy will minimize bubble generation.

About Resin Designs Epoxies

Resin Designs makes structural, non-conductive epoxy adhesives that don’t melt when exposed to heat. Our epoxies are rigid and have great chemical resistance. They’ll also cure at room temperature and will cure faster when heat is applied. Check out some of our custom epoxies, including the Nexus 84301 and Entex 84251.