Are all polyester resin the same?

[Kez]

I need a small quantity of polyester resin to lay up a homemade fuel well and to glass in a couple of rails. New to the area and still don't know where the local suppliers are. Walmart carries this Bondo resin meant for body work. It is a finishing resin (wax added), which is what I need. But is it as strong as laminating resin meant for layup?

kez

 

[shadow]

Yes for common hobby use it is the same thing as other polyester resins. It just doesn't work well for gel coating!

Good luck,

Cliff

 

[Mark Poole ModVP]

The resin that is sold at hardware stores and walmart is almost always finishing resin. It has wax additive in it and is a thicker resin than laminating resin. The wax really does not cause any lamination problems. This thicker resin can work better for glassing on vertical surfaces because the resin will not run out of the cloth as easy. If the boat that you are going to do this to is made of epoxy then I suggest you get some epoxy resin. Polyester resins do not bond well to epoxy surfaces.

Mark

 

[HTV Boats]

Any general purpose resin should work. Should be strong enough for hobby use. Wax in resin comes to the surface during the cure to cut the resin off from the air which retards the cure. If you were doing laminations in stages you might want unwaxed resin so layers would fuse together better. Lite sanding or scuffing waxed resins works fine between layers. Polyester resins are pourous and water will wick through them. Thats what gel-coat is for. It is a polyester composition that has a harder surface (more brittle and less flexible) and is not pourous. When you lay up a boat in a mold wth gel coat as the outside surface it cures from the outside in. If you notice how resin stays sticky its because it is not cured where the air is exposed. When doing repairs you commonly use something like PVA (poly vinyl alcohol) which dries and leaves a water soluble vinyl on the surface which cuts off air to promote a full cure. Polyesters cure slowly and full hardness can take days to weeks. When you pull a part out of a mold daily the parts are probably 90-95% cured. Ergo keep a new hull on a flat surface. I have let race boats sit in a mold for two weeks before pulling it. mass produced hull can't take that time. This is why two boats out of the same mold may perform differently.

Epoxy resins are not chemically comptable with polyester and though more expensive will cure fully in a shorter time. Epoxy is in general about 75 to 80% of the weight of polyester. Harder to lay up and doesn't wet out as well and tends to puddle, so if not careful you don't get a lighter part. A bit less flexible than polyester and shears easier on impacts but stronger in general. Better boat if done right. Don't fix or mix polester or epoxy together. If your hull is polyester (commonly called fiberglass) keep it all polyester.

If you look through a resin catalog there are literally hundreds of resins with many different properties. From rubber like to fuel and acid resistant. High heat resistant that is used in exhaust systems. What you find in the retail environment are basically GP or general purpose resins. Too expensive to stock exotics.

 

[Kez]

Thanks all for your replies. I am aware of the incompatibility between epoxy and polyester. I just don't have a lot of experience with the autobody resin. Will pick up a can tomorrow.

kez