Resin

[Russell Sova]

I use epoxy for boat building, but I also use polyester resin. I've read here where people contend that polyester resin will definately delaminate over time. Why does Marks' Handbook for Mechanical Engineers state that polyester sticks to wood at an 8 out of 10 rating. Believe it or not it says it sticks to metal at a 2 out 10 rating. I've never seen the stuff fall off of old car doors even though they were slammed. I've seen the stuff really soak into wood and remain flexible.

[thechemist]

If you wait long enough, interesting things happen.

The mechanisms of chemical or mechanical adhesion depend on surface preparation and the presence of chemical pretreatments for metals [all chemically different, and different pretreatments required,] and adhesion-promoters in one or both sides of various resin systems.

For instance, most resin systems will not stick well to clean steel, where many will to steel treated with phosphoric-acid-containing products to phosphate it, that meaning growing a layer of iron phosphate crystals on the surface. The chemical reaction creates iron phosphate chemically bonded to iron, and other things are actually sticking to the iron phosphate, not the iron.

With age and other factors polyester [the word means many esters] resin decomposes by ester-hydrolysis to yield delaminated goo. Thus, if whomever did the original tests aged their specimens underwater first, results might well have been the reverse or worse.

[JimD]

Chemist, promise you'll never quit the forum? smile.gif

[Russell Sova]

Thanks chemist I wrote that hoping you'd reply with some science. Does this delamination goo cause the wrinkling of polyester I see on my neighbors old Dodge?

[paul oman]

I get frequent calls about polyester resin and fiberglass cloth disbonding from wood hulls after about 8 -12 years. I experienced this personally with an old thistle class sailboat I had as a kid....

paul oman
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[TimH]

Polyester - BAD Epoxy - GOOD

smile.gif

[Carl Simmons]

Does Polyester bond better to some woods then others. For example, would the bond to mahogany be 8-10 years where cedar 6-8years?

[thechemist]

Polyesters are relatively rigid compared to wood, and the wood expands and contracts with humidity variations and the polyester-laminate doesn't, and thus you get failures by shear delamination.

Resins of any kind used the wrong way will cause problems. Some people use WEST to fill the seams in their wood runabouts of plank-on-frame construction. What happens eventually [and it only takes one or a few seasons] is that after mechanical vibration and humidity-cycling movements, the rigid epoxy shears from the wood [or, to put it another way, the more flexible wood fails one fiber layer below the epoxy-wood bond] creating "zipper-cracks" that run some length along one side of each epoxy-seam.

Wood generally has a shear strength of only a few hundred pounds per square inch. If adhesives or laminates bonded to it cannot elongate as much as the wood without their tensile modulus developing a shear stress of that much, then the stuff comes loose from the wood.

It's a natural principle. The palm tree resists the force of the hurricane, and is uprooted. The bamboo yields before the force of the hurricane, and so survives.

[Russell Sova]

Thanks guys for the input. I've bent the polyester back and forth pretty far before it breaks. Is this only when it's new? I can't imagine the wood flexing more than a 1/8 of an inch or so.

[oldriverat]

I wouldn't use polyester resin if I were you. There have been hundreds of thousands of boats built with that stuff throughout the years and all of them sunk. I built a skiff with it three years ago and it sunk too killing all onboard except myself. That stuff is no good!

[ 08-05-2003, 06:33 PM: Message edited by: Memphis Mike ]

[JimD]

Originally posted by Memphis Mike:
I wouldn't use ployester resin if I were you. There have been hundreds of thousands of boats built with that stuff throughout the years and all of them sunk. I built a skiff with it three years ago and it sunk too killing all on board except myself. That stuff is no good!Mike, as I recall you were the only one on board, and it wasn't a boat, it was a polyester bathtub duck, and it wouldn't have sunk if you hadn't sat on it in the first place. But I'm with you, epoxy has its advantages.

[NormMessinger]

Originally posted by Russell Sova:
Thanks guys for the input. I've bent the polyester back and forth pretty far before it breaks. Is this only when it's new? I can't imagine the wood flexing more than a 1/8 of an inch or so.So why did you ask the initial question? If you think that is a vaild test, go to it.

[Russell Sova]

Heepum not sure. Needum input.

[CKG]

Wasn't Dynamite Payson using polyester resin and fiberglass on a whole bunch of boats? Seem to recall that in those great articles and illustrated instruction books he wrote, it was polyester. Have built surfboards and many small boats, myself, using the same. Friends, family, paying customers and myself had - and continue to have much fun, in and on these craft.
The projects that failed, either initially or later on were a result of early inexperience, inappropriate application, or inattention to maintenance.
None of the failures were catastrophic, or complete.
The desire to build and get out on the water promotes much experimentation. If you can afford good material, use it. If you feel you can' t, don't.
If you can, keep your small boats dry, clean and out of the sun when not in use and they will last as long as you will, if you treat yourself the same.

[Dave G]

Really interesting thread.
I coated the deck of my wooden plywood 110
this past winter with epoxy and a layer of cloth. Just as the Chemist suggested it is starting to pull the chine apart like a zipper... Is there a way to prevent this? Or to do a better job next time..?

[thechemist]

When one layer of light-weight cloth is put on a wood substrate, sometimes the wood moves [the separate pieces move with respect to each other] and tears the glass-resin laminate.

Is that what is happening?

[Dave G]

Unfortunately, its tearing or peeling the wooden chine... I guess in places it might just be the cloth. But for the most part it's tearing an inch thick crack right up the side. The epoxy and cloth are clearly winning the tug of war. It's probabaly 4-feet long