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Epoxy - Slow Cure vs Fast Cure - Which is Best?

Question: Epoxy is available in different cure speeds. Should I use a Slow Cure (30 Minute) or a Fast Cure (5 Minute) Epoxy?

Short Answer: Use 30 Minute Epoxy where strength and structural integrity is important such as when joining wings or mounting stabilizers, engine firewalls etc. Use Fast Cure for quick repairs of small non-critical components or joints. If in doubt, always use 30 Minute Epoxy.

Better Answer: There are two general factors to consider,  Bond Strength and Working Time. 30 Minute Epoxy creates a stronger bond and it gives you more time to work. 5 Minute Epoxy gives a good bond but it is not as strong as 30 Minute Epoxy and it must be used very quickly, particulary in warm conditions.

The Bond Strength is pretty straighforward... 30 Minute simply gives stronger bonds. Use 30 Minute when joining wings, installing stabilizers, engine firewalls or other load bearing critical structural components that you simply cannot afford to have come off or fail. Use 5 Minute Epoxy for quick minor repairs of non-load bearing or light load bearing less critical components.

The Working Time is something that modelers frequently overlook and tend to err a bit in favor of  "fast is good". In some cases, like a quick repair of a simple small component... fast is really nice! But in cases where the amount of adhesive is considerable, the components are large or complex and/or need to be simultaneously mated with other parts.... you need to allow for plenty of time to work in order to get the parts aligned and properly placed. It is very important that the Epoxy is fully "wet" when being used. If Epoxy starts to thicken at all before the parts are joined, the Epoxy will not produce a good bond.

The worst possible scenario is using 5 Minute Epoxy on a complex multi-piece job like joining a wing. We have had too many calls from people who end up with the Epoxy beginning to cure before the wing halves are properly joined. We have also seen wing joints after in flight failures caused by gummy thick half cured Epoxy not penetrating and filling the joint and component substrates properly.

If you have any doubts about the complexity of a job, need for strength, working time etc, always use 30 Minute Epoxy!

Article ID: 2688