Polyester Resin and Plywood

Everybody who has been around boat yards since the 70’s is familiar with old home made plywood trimarans (usually but not always) with the fiberglass falling off in big sheets. As a result, polyester resin has got a bad rep as a plywood/cloth coating, and today most people use epoxy which sticks much better. However, epoxy costs MUCH more than polyester! Over the years I’ve heard various ideas to make polyester stick and I know some work because there are many old old glassed plywood boats out there. I’ve been told one system is to mix some resin “weak”(but HOW weak?) and paint the wood with that. After a couple days, you then glass the boat. I never tried it. Anyway, John Riding in France sent these comments regarding Polyester resin. It sounds interesting!

“I would like to add a little, namely, that the chemicals present in all wood, can and do inhibit the curing of the polyester resin that actually soaks into the wood.So a resin seems cured, and on you go, and add a bit more glass, then finish it all off, then some years and several thousand twists and shakes later the whole darned skin tries to fall off. The resin never cured IN THE WOOD. I learnt fiberglass from one ofAustralia’s masters, Geoff Baker, who had a factory in Mona Vale, Sydney, and built Illingworth ‘Top Hats’, and the various Brolgas and Boomerangs from the board of Peter Joubert.

Geoff was adamant; Use cobalt napthanate, the standard ‘accelerator’ additive, 2% or a little more if the wood was ‘green’, added to the resin BEFORE adding the catalyst. The CN is explosive when directly in contact with catalyst, so TAKE CARE. Mix it well with the resin before catalyzing. With this accelerated brew, paint a primer coat on all the wood to be glassed. It will go off quickly, but, most importantly, will cure right into the wood, and will never let go. Continue with whatever layup you fancy from hereon; the stuff is now well bonded. It will fix those rudders that keep shaking their skin off.”

BMW sells this slick scooter in Europe but for some reason, not in the US. It’s amazing. What’s this got to do with polyester or boats? I dunno. To quote Dean Martin likeI do probably to much; “just tryin’ to have a little fun, folks!”