Epoxy resin over poly resin ???

[lobsterman]

Hi all,
Can epoxy resin be used over poly ???, I am building a 12' stitch and glue skiff, and i have done the bow and transom seams with a filler and covered them with f-glass cloth tape with poly resin (the twisted copper stitches were left in, and encapsulated in this). I have yet to filp it and install the bottom sheets, (as i am working outside and the weather has not been too cooperative yet ).
But after reading all the benefits of epoxy rather that poly, i am wondering if i could do the exterior of the hull with epoxy, now that i have already done a few seams with poly ???.

Also when covering the hull should i use cloth, mat, or the new combo stuff that they are now selling ???. ( i am trying to keep it light, but i am unsure what bonds or holds up the best ). Thanks.

[david@boatsmith]

The problem with the poly in this application is that it tends not to bond permanently to wood. Epoxy is a much better choice for this. epoxy sticks fine over poly, poly over epoxy is a little tricky. For sheathing I prefer cloth. i also sheath with xynole polyester cloth as opposed to fiberglass cloth.

[lobsterman]

Thanks David,
I am still wondering if i should just stick with the poly, as it is basically just a lumberyard type of lobstermans rowing skiff, that is just getting a glass skin over it, and i should probably try to keep it as cheap as possible, ( i wish i could've afforded marine ply when i started this project ).
Also, i just get my fiberglassing supplies from a local commercial fishing supply company, as i can afford them, so my choices are kind of limited.

For not using anyone elses plans, and only using my own ideas for it, I must say that i do really like the lines and the looks of the way it is coming along soo far, and i am already contemplating building another one, to better standards. Dam, i wish someone had warned me that this boat building kick is soo addictive... ( and expensive !!! )

[gonzo]

With polyester and mat, you can look at a few years of service from the boat. I have built a few with carefullly picked CDX and polyester. With the original two coats of paint, they survived over three years. They were always outside, either in the water or laying on dirt.

[PAR]

As has been pointed out, polyester isn't the best choice on wood. To directly answer your question, yes, by all means switch to epoxy as soon as practical. Epoxy is twice as strong and considerably more waterproof too.

The inside corners of a tapes seam builds (stitch and glue include) is the most important part of the joint, usually bearing a high percentage of the load transfer. A layer of cloth over the polyester tape job will go a long way to stiffening these areas up, though they'll still be relying heavily on the polyester/wood bond.

You don't need, nor is it desirable to use mat with epoxy. Besides the obvious weight advantages of this, is also the fact you'll use 2/3's less resin to wet out the fabrics.

On a down and dirty build you should weigh the costs and effort against what you want from the boat. If it's a short term project, then skip the epoxy and the external sheathings and just paint her after seaming it up.

[lobsterman]

Well thats encouraging, in a depressive kinda way, as i was hoping to get about ten years out of it. Oh well it is a fun project anyhow, and i can't wait to take it out for a test row.