Many glue failures in wooden boat construction happen because of end grain gluing. End grain is much more absorbent than other surfaces. There are simple strategies to reduce the risk of end grain bonding failures.
See drawing of endgrain right..
The basic problem is that end grain is highly absorbent so it can steal the resin from the join leaving insufficient for good bonding. The trick … is to feed the end grain some mixed resin before the glue mix is put on
Remember that generally epoxy needs to have the correct powder modifier added to the mixed resin and hardener for most types of gluing.
When gluing endgrain with epoxy it is a two stage process.
The Two Step Process to ensure that End Grain doesn’t become glue starved
Any variation of end grain. But joins, scarf joins. Note that scarfs of a minimum 6:1 are required for strength. Plans may specify specific angles of scarf joins that are 8:1 and above so follow the advice in your plan. My design structures have proved reliable at 6:1 over many many boats and projects IF the end grain is dealt with using the method below.
- Mix enough resin and hardener to do the job. Stir well. Brush the mixed epoxy onto the endgrain.
- Wait 5 minutes. This allows the epoxy to soak in. Brush more epoxy on the endgrain.
- Now add the high strength gluing powder to the epoxy in the container and apply to gluing surfaces.
- And hold in place by normal method – clamps or temporary fasteners or tape until the epoxy sets up.
