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Re: polyester resin for tortured ply?
By:Paul Jacobson
Date: 3/8/1999, 7:05 pm
In Response To: polyester resin for tortured ply? (David Blodgett)

> Every one was talking about cedarstrip. Will it be strong enough for a
> tortured ply? what should I do differently? Thanks Dave

Tortured ply is just stitch and glue. My 5 year-old copy of Clark-Craft's price list has a one page summary of how to do stitch and glue. They specifically mention using their polyester resin and polyester-based filler.

After reading that, my question (for a while) was: Would epoxy work for this?

Well, time seems to have shown that either resin works.

I would be careful with using the correct width of fiberglass tape, though. The bonding strength would be related to the area the tape made contact with. Some engineer would probably measure this in terms of adhesion per square inch. If you can't make it more adhesive, then give it more square inches.

As for additional layers of tape. I'd go with the designer's specs. This is like comparing a dictionary with a single sheet of paper. Try cutting through a sheet of paper. Then try cutting through a dictionary. Set a dictionary on the edge of a table and it stays rigid. Set a sheet of paper in the same place and it sags.

Similarly, the addtional layers of fiberglass tape have greater resistance to being cut, more stiffness and strength. If the bottom layer does not adhere well to the wood, though, then addtional layers won't help the adhesion. What they will help is this: Those several layers of tape create an exact and perfect-fitting channel of reinforced plastic that supports the wood along the entire length of the joint. Since it is manufactured in place from a liquid hat flows into every nook and cranny, this joint has such a perfect mechanical fit, the amount of adhesion between the resin and the wood does not need to be very great in order to get an extremely strong and durable joint.

In general, epoxy resin is considered stronger, more impact resistant, and more flexible than polyester. Similarly, titanium is stronger than aluminum. However, I have an aluminum step ladder at home. It was designed to do the job, and it does it well. I could never afford one made from titanium.

Hope this helps.

Paul Jacobson

Messages In This Thread

polyester resin for tortured ply?
David Blodgett -- 3/8/1999, 8:11 am
Re: polyester resin for tortured ply?
Paul Jacobson -- 3/8/1999, 7:05 pm
Re: polyester resin for tortured ply?
Nolan Penney -- 3/8/1999, 9:23 am