A common problem of older outboard motor boats is transom delamination. The great weight and load these structures must bear eventually creates cracks, allowing moisture to enter the core, ultimately leading to serious structural damage.
Solution 6 - Repairing outboard motor transom delamination
1. Remove outer fibreglass skin using a router pre-set to cut the depth of the skin. Save the skin if possible.
2. Inspect core material. Dry thoroughly using a hot air gun or heat lamps. If minor core damage is evident, remove damaged material and dry the cavity thoroughly. Coat damaged area with epoxy, then fill voids with epoxy thickened to a "peanut butter" consistency with 413 Microfibre Blend.
3. If major core damage is evident, remove the entire damaged core section, leaving the inner skin intact.
4. Laminate pieces of marine grade plywood to the proper thickness to replace damaged core sections. Use the old core sections as a template. Pre-coat plywood pieces with epoxy thickened with 413 Microfibre Blend.
5. Bond the new core section into place using liberal amounts of thickened epoxy, clamping in place until cured. Epoxy should squeeze from joints when clamped; remove excess epoxy.
6. If you were able to save the outer skin, bond it back into place with 403 Microfibre Blend-thickened epoxy. If the outer skin was not salvageable, laminate four to six pieces of 400gm/m2 fibreglass cloth (match original skin thickness) using unthickened epoxy.
7. Reinforce corners with four strips of 300gm/m2 fibreglass tape and epoxy. Cut and position each successive strip 50mm narrower than the last. Allow to cure.
8. Fair to hull contour using epoxy thickened to "peanut butter" consistency with 411 Microsphere Blend. Allow to cure. Sand fair and smooth.
9. Apply several coats of unthickened epoxy and allow to cure 24 hours before final sanding and painting.