Resin for Fibreglass and Gelcoat Repairs

Question:  There are several cracks in the interior of my boat and one gouge about an inch and a half in diameter on the bottom of the hull next to the bailer. Would the Tasar take standard fibreglass repair techniques or does the foamcore require something different?

Thanks, Burt

Answer:  Resins which cure chemically have a "green" period between gel and full cure during which another coat of the same resin will form a solution bond with the existing laminate which is very strong. This is the principle used for normal layup, whether polyester, vinylester or epoxy. This period is typically one to several days depending on temperature and desired rate of cure ("Hot" mix etc.)

A different resin applied during this "green" period will not disolve and bond with the substrate, and will soon fall off. Once the resin has fully cured it becomes insoluble to its own solvents (and ay other solvents), and any repair must rely on a mechanical key for grip.  So any repair starts with masking the area to be glued and roughening it with coarse sandpaper, 80 grit at finest, to give the new resin a key to surround and key onto as it wets the surface.  Since no solution occurs, there is no reason why a different resin system should not be used.

In practise polyester will not stick to epoxy for a surprisingly long time. Epoxy sticks to polyester sooner and generally better as it is a stronger resin. So it is good for mechanical repairs, but if you then want to repaint with polyester gelcoat you are stuck with the problem that polyester does not like going over epoxy. For this reason polyester boats are usually repaired with polyster resins and then painted without trouble with polyester gelcoats.

Hope this helps, Frank Bethwaite

Question:  Frank, were the old boats (ie 1976 vintage) also made with polyester resins/gelcoat?

Colin Goldrick

Answer:  No Tasars have ever been made other than with polyester resins and gelcoats.

Frank