How2make Polyester stick to plywood...

[woodenMFV]

...would be a great solution! #

Yes, I know, a really often mentioned problem, and easy to solve...in simply using epoxy instead :)

But my reason, researching on that old problem (trying Polyester and not Epoxy) is just the SIZE of the area to cover; I'm building an all new plydeck 52ft x 16ft what would need something around 20 gallons of resin plus the glass cloth plus hardener.

And the price of Epoxy in UK (you lucky one's overseas) ...its very expensive here, lot more than in US (after a while I just stopped searching for some cheap epoxy; even did not find some "industrial use"-epoxy, from which is said it's equal quality, just has'nt that broad-temperature-range - but of course much cheaper than the marine stuff. Seems over here exists a kind of "epoxy-kartell",keeping prices high *g*)

So, I looked through a lot posts about "fibreglass-topic"; one guy posted an interesting link to good-old-backyard-buehler's page, where someone wrote about a way to make that (stinki)Polyester stick to our plywood: "...use cobalt napthanate, the standard 'accelerator' additive, 2% or a little more if the wood was 'green', added to the resin BEFORE adding the catalyst..." link (http://www.georgebuehler.com/Polyester%20and%20Plywood.html) He also describes WHY it normally don't stick; all makes a bit sense to me, but I'm no expert in that field (as you expected of my questions)

Hm, any chemist around here to cope that description above? Maybe that works, what do you folks think?

PS: I hope George Buehler excuses me the "old" in "good-old" ;) I can't imagine my bookshelf without his book "backyard boat building" (though I suppose my ol'bathtub never saw any backyard even from far)

[MiddleAgesMan]

Google Dynamite Payson. He was using polyester and glass on fir plywood boats at one time. He wrote about what he used to prep the plywood but I can't recall what it was. It might have been acetone.

[ssor]

Try this link . I haven't explored it fully but he recommends chopped strand mat for the first ply.
http://www.ericgreeneassociates.com

[MiddleAgesMan]

Fiberglass cloth, by itself, doesn't work well with polyester resin. However, if you lay a combination of mat-roving-mat on dry plywood you wouldn't be able to get it off with a shovel.

No resin required? ;)

[MiddleAgesMan]

Sounds like something you could use if you needed to reduce the plywood thickness a little. I don't think it would save you any money but it might give you a more bullet-proof hull.

[Driver Mark]

At unclejohns.com they have plans for pirogues,skiffs and jon boats and one of their suggested methods involves diluting polyester resin with acetone to make it penetrate the wood and form a better bond.
I used this method on a stitch and glue D4 dinghy and it has held up pretty well so far it's 5 years old and still holding together.
I know polyester is frowned upon as an adhesive but it seems to work.

[jclays]

For my large engine hatches I rolled heavily the poly resin thinned 30% with acetone onto the plywood. I layed fiberglass mat onto the wet poly covered plywood. Smoothed the mat and then applied un-thinned Poly resin to the top. rolled 3 coats untill all weave was filled. Solid should last another 40 years like the first time.

[Todd Bradshaw]

"Fiberglass cloth, by itself, doesn't work well with polyester resin. However, if you lay a combination of mat-roving-mat on dry plywood you wouldn't be able to get it off with a shovel."

Sorry folks, but both of these statements are baloney! Fiberglass cloth works perfectly fine with polyester resin and the laminate schedule used has absolutely nothing to do with how well it will stick to plywood. That is strictly a matter of the resin used. The decision of whether you use mat or cloth is one of what characteristics you want out of the laminate, not which one will work. Cloth has higher tensile strength for a given amount of weight, mat has higher higher stiffness, less tensile strength and tends to soak up a lot more resin. There are also numerous combinations of chopped strand layers stitched to woven (or non-woven, warp-sheet-style layers of continuous fiber bundles) or biaxial layers to combine the characteristics of the two types. They can get really pricey, but there are some good ones available.

Your main problems will be inadequate sealing of the wood and the rot it can lead to and poor bonding to the wood. There are pretty drastic differences in the bond strength of different brands and formulas of polyester resin, even if you stick within the sub-category of unwaxed laminating resins suitable for boat construction (which is most likely the type you should be using). We spent about four years back in the 1970's experimenting with different polyester resins for strip canoes and finally arrived at one particular resin (Techniglass 329-2, most likely long gone from the marketplace). It was a laminating resin formulated originally for factories doing fiberglass layups in the Pacific Northwest or areas with similar weather. We found that a primer coat or two of laquer sanding sealer on the wood improved the peel strength substantially. We eventually got to the point where the layup would usually withstand a pretty serious collision between a fully loaded canoe and a rock with obvious local damage, but without a big delaminated area. Compared to nearly all of the other polyesters and primer systems, this was a big advance. When epoxy came along though, switching was a no-brainer. It seals better, sticks better, is safer to use and is easier to use.

In my opinion you're crazy to spend all that time and money on a polyester fiberglass covered deck that is almost certainly going to fail prematurely and ruin the wood under it. The cost savings does not justify the risk and the problems involved. It would be a tricky and very questionable project even if you had lots of experience with the products and knew how to use them well.

[MiddleAgesMan]

I misunderstood. I thought he was building a deck out back, behind the house. ;)