Can You Use Vinyl ester Resin for Cold Molding?

This is purely hypothetical, so humor me, what are the reasons for not using Vinyl ester (or polyester for that matter) for cold molding or strip planking a wooden boat. Obviously, it has to have some sort of drawbacks since they are much cheaper than epoxy and if they were equal, you'd see cold molded or strip planked boats built with vinyl ester or others. I know other glues have been used i.e. resorcinol and I've heard of a few boats built with Gorilla glue due to the builders severe epoxy allergy.

 

Because they are not formulated as "glue".

 

In my experience gorilla glue is well suited for gluing up strip planking with structural foam; san, pvc or pet. Wouldn't use anywhere else. My only experience with vinyl ester was fiber glassing a wood strip canoe years ago as a demonstration project. Advantages; quick setting, slightly lighter weight and a lot of UV resistance. Disadvantage was I wasn't familiar with the product and almost freaked out while glassing the hull.

 

It can be used. Try some wood scraps and see.

 

Vinyl ester and polyester aren’t typically used for cold molding or strip planking because they don’t bond as well to wood, are more brittle under stress, have lower water resistance, and lack good gap-filling properties. Epoxy provides stronger adhesion, flexibility, and protection against rot, making it far more suitable for wooden boat construction despite the higher cost.

 

Epoxy without a thickener does not have better gap filling than vinylester or polyester. In fact, the latter are thinned with styrene for better flow and wetting characteristics. Without a solvent they are like honey.

 

Plenty of top end boat builders have used polyester on balsa cores, and vinylester has been used as an osmotic barrier coat as it is more waterproof than polyester. Sure, there are stories of how polyester-glass sheathing fails on a 30 year old amateur built boat. I do not mind paying for epoxy as the cost comes down when bought in bulk, but i would be surprised if vinylester bonded wood joints would consistently fail before the wood, depending on wood species and resin fillers. I think there was a guy on you tube who has done plywood and foam test panels for most resin and fabrics.
The bigger question, is the wood being used as a core for heavy structural skins, or the is the wood itself the structural element with only light sheathing for protection. I have seen some wooden boat "restorations" that involved drums of epoxy and bog and the end result works in a way that polyester bondo never did.

 

A friend of mine did tests bonding WRC strip planking with VE thickened of course with silica and, as you would expect, the failure was in the wood. The biggest problem with using it in place of epoxy for cold molding or strip planking would be convenience, it's hard to beat using an epoxy pump for convenience, either way you will be adding extenders to make it thixotropic. Also you are probably going to want the working time of slow hardener while VE is better catalyzed at 2%. Flexibility would not be an issue as a lot of VE formulations have better elongation than the many of the most popular epoxies. I never use polyester for anything these days so would not personally give it much thought.