: I am doing a project on canoeing materials i am studying polyester resin
: could you give me any info it would really help thanks

I don't know your time frame on this, but if you can wait for the mail:

Clark Craft's free price list used to have a full page discussion on polyester resin, and they had other information in their catalog ($5) You can get details on ordering these from their website. (www.clarkcraft.com)

Fibreglast has info on these materials in their catalog (www.fibreglast.com)

David Hazen's old book on strip canoe building used to have information of interest, but you may have to look for an older edition. I believe this title has been updated to include more info on epoxy materials.

As I understand things, basically, there are two problems with polyester. 1) It does not bond well when used directly on some woods -- particularly those that are a bit oily. Red cedar falls into this category, but white cedar is not a problem. (You solve the problem by applying a sealer to the red cedar canoe before glassing it.)

The second problem is that there is a solvent in the resin which evaporates as the resin cures. As the solvent makes its way out of the plastic it leaves behind microscopic tunnels that formerly contained the solvent. These tunnels are way too small to allow liquid water molecules to enter. However, in water vapor the molecules are very small and over time watervapor can penetrate the plastic. If sufficient vapor gets through, then heating and cooling cycles cna cause some to accumulate as liquid water in the area between the wood and the fiberglass and resin. Sometimes rot can develop under the fiberglass as a result. This tends to be more of an issue with larger boats that are constantly kept in the water.

On the plus side, polyester is cheaper. I bought a gallon of the stuf for $14, and others have gotten it for a few cents less. The price usually includes the activator (or hardener). Working with polyester is different too. You adjust the amount of hardener depending on the temperature or your desired potlife, so you don't need to buy separate slow or fast hardeners. The UV resistance is much better than with epoxy, so you don't need to varnish -- though many people do. The material is thicker, so you get better build up.

Polyester resin comes two ways. Normally the material will harden, but stay tacky in the presence of air. This makes it nice when you are putting on several coats of resin. No sanding needed between coats. For the first coats this is fine. for the top layer you either use a form of resin which has disolved styrene plastic and parafin. These migrate to the surface and block air, allowing the resin to harden completley. Saran wrap does the same thing. So does spraying the damp surface of the final coat of resin with a parting agent or mold release compound. If you use the resin with the wax and styrene includedm you need to sand this layer off before applying another coat. Otherwise, your sanding is reduced.

Hope this helps.

PGJ