Adding extra hardener (don’t)
While adding extra catalyst to polyester resins can lead to a faster cure, you should never add extra hardener to epoxy resin. Epoxy reaches cure when the resin molecules cross-link with hardener molecules. When there is too much of either resin or hardener, unlinked molecules are left over. This can result in uncured epoxy or compromised cure strength. Always mix epoxy resin and hardener as close as you can to the recommended ratio.
Unlike traditional wood glues, WEST SYSTEM Epoxy is stronger than wood. Because of this, it is beneficial to have some epoxy between the objects you are gluing together whether they are wood, fiberglass, or other materials. As long as the epoxy is contacting the entire surface of both substrates, no clamping pressure is needed.
The goal clamping is to simply ensure the epoxy contacts the entire surface for the duration of the cure time. Moderating clamp force is all you need. If you aren’t using a filler, and apply too much clamping force, this can result in a glue-starved joint. This makes future joint failure much more likely. Glue starved joints are weaker than their counterparts. Avoid glue-starved joints by following the one- or two-step bonding method.
Filler and Epoxy Strength
While certain fillers will increase the density of epoxy, this does not correlate to higher physical properties or increased adhesion strength. Epoxy is strongest without filler added to it, but the fillers are necessary to:
- Increase the viscosity of the mix
- Bridge gaps
- Prevent the epoxy from soaking too far into the wood
- Prevent glue-starved joints
Epoxy and Rotted Wood
Rot eats away the cellulose fiber in wood. Cellulose is the structure of the wood. Replacing it is not as simple as brushing on a coat of solvent-thinned epoxy. Solvented epoxy may replace some of the strength, but isn’t a permanent repair—it won’t restore the strength of the wood fibers. To make a permanent repair, replace the entire rotten area with fresh wood and sealed with epoxy. Addressing rot this way will make the repair area stronger than it was before the rot occurred.
Why remove rot?
Rot needs four major components in order to continue growing:
Cutting off just one of these components is enough to cause the rot to go dormant. Solvented epoxies are supposed to cut off rot’s food source by encapsulating and contaminating the wood that the rot spores consume. However, the remaining three components: moisture, oxygen, and warmth, can still penetrate wood coated with solvented epoxy.
This is because solvented epoxy is a poor moisture barrier. Rot spores will remain in the wood, and even when encapsulated in solvented epoxy, they will only go dormant. Un-isolated rot pores will continue devouring the cellulose, causing more rot.
This is why we recommend removing the rotten wood and replacing it with fresh wood that is sealed with several coats of WEST SYSTEM Epoxy.