Polyester resin as a primer?

I tried searching old threads so as not to waste anyone's time, but got only more confused. The woodwork on my skiff project is complete and now I am ready for the paint and finish stage. I was planning to coat all surfaces with polyester resin as a sanding sealer. I need advise. 1. Is this a bad idea? 2. Would resin be compatible to all oil base marine paints, or should I avoid some? How long should the resin cure between coats? If these questions seem too elementary, could someone direct me to some literature or website. Thanks

 

Polyester resin can be used as a sanding sealer, but it's not very good at that particular task. Polyester just doesn't stick very well to wood. Just ask anyone with a 20+ year old fiberglass boat, who's stringers and other wooden elements were coated with polyester resin (most are rotting and delaminated). Vinylester resin is much better the polyester and epoxy is hands down the preferred material on wood.

This said, these resins are costly and messy to work with. I suggest using plane old 3 pound shellac, which is available from your local hardware store. Shellac will seal the wood, better then varnish or clear polyurethane and even better then some of the lower grades of polyester resin. Soak the wood repeatedly with this stuff, until it has a uniform shine all over, with no less shiny areas showing. Thin coats, probably three will be necessary, then paint your heart out.

I say this considering the nature of your build Crosscut. You're not making a 18th century restoration or replica, just a boat you want to use, preferably in short order, now that the weather has turned. In fact, coat every piece of raw wood you see with the stuff, it'll work fine on your little power skiff.

If you want maximum durability, then epoxy is the ticket, but expect to pay for it. If it were me, I'd use epoxy around the engine and fuel tank areas (shellac doesn't like petroleum products) and shellac everywhere else to save effort and money.

 

Great response Par. You are correct this boat will be my knock around, loan out boat. I never thought of shellac, although I did know it is a main ingredient in some painting primers. I do have some poly resin and might use that around the motor and battery box. Thanks, all suggestions welcomed.

 

Over the years I've kinda got a bit disrespectful of polyester, but it has done me some good turns over the years. Like complicated sill flashings before E2, the moisture code came out.(With all the proprietary flashings that you have to use to comply now) Also, flashings for roof windows (with a bond breaker of course) and repairing broken sewer pipes. I slander it for its adhesion, but when you think it ain't going to stick, it sticks like hell. It sticks great to oxidised zinc roofing iron.
I guess it started when we used cedar stingers in surfboards. Bloody things used to fall apart and the cedar retarded or stopped the reaction completely.
And it doesn't like mdf either or masking tape (3m) paper type. Stays sticky as hell. If the wood is high resin/gum don't expect a good result with poly.

Not that this is relevant but riding epoxy as compared poly is kinda like a rubber band to a guitar string.Low verses higher modulus. The poly snaps back quicker.

 

Crosscut, pick up a quart of epoxy and use that around the nasty areas (battery box, tank, engine well, etc.). It sticks to wood so much better, I hesitate to recommend polyester for anything on wood.

 

I do have some epoxy left over from the build, then it looks like shellac the rest of the way. Thanks