polyester over plywood: advise needed

[rwatson]

Originally Posted by pescaloco

Alan,

Thanks for the info on the overcoating.

My original concern is that if the sheathing were to delaminate it would be from the polyester to wood interface. Since there is nothing that can be done to improve that bond, looks like the next best thing is what we have been discussing.

Thanks

A recent article in "professional boat builder" addresses this issue with tests and processes described.

Essentially, you get a far better result if you apply f/g to the ply, let it cure to touch dry, then apply the cloth.

Probably worth a read.

[tunnels]

polyester over wood !! dosent work ok !!! take my adivce use epoxy!!

[rwatson]

I took the liberty of printing a copy of the article in PB, and have attached it.

The article talks about making it easier to apply polyester to plywood, and you can see a guy laying polyester and cloth over what looks like a stringer in the bottom of a powerboat.

Whats more, it discusses this being the engine bay. I wouldnt like to have to inspect the plywood after a couple of years of water and oil sloshing around the bilges.

However, I suppose this type of boat is only ever taken out on weekends, and washed downs and drained lovingly on the trailer, and kept in a garage.

It will probably be ok till the next engine replacement.

PS - note the Ad for the moisture meter on the same page!

[PAR]

Polyester on wood can work, but by the time you apply enough material (fabrics and resin) you pretty much don't need the wood anymore, as it becomes self supporting. No production manufactures that I know, of are using enough are using enough materials to insure durability. The vast majority of these boats don't retain their resale value very well, so by the time their hour meter hits mid triple digits, the boat isn't worth enough to warrant repair, it's just dragged to the land fill.

People read a little or hear someone say something and for lack of a self-formulated opinion, they adopt another's. Next thing you know, it's repeated enough that the concept begins to grow exponentially - a wildfire.
Listen, epoxy adheres far better than poly and if there is a lot of movement and a little moisture where it's not supposed to be, the poly delams. There is poly on some web frames and bulkheads on my boat that has been there since 1979. I, last year, put a layer of the finest cloth I could find over it just to make it look nicer, more even, for painting. I could find no soft spots or delams in >< 64sq.ft. Water, gurry, ice, decades. I prefer to lay the cloth into a tacky second coat of resin - that way you can get the fabric exactly how you want it. If it were on a place of large concern, or l wasn't trying to save money, I'd use epoxy, too.

[tunnels]

Poly over ply has a initial stick but will eventually part off the surface and or take a percentage of the first veneer with it , Wood exspands and contracts and poly also moves but at differant rates . so somethings gat'a give and its the bond or the weakest part .
In the bottom of a boat wooden boat over stringes you are playing with danger!! and its not worth the effort , time ,a exspence , just bite the bullet and epoxy it!!!!You are saving nothing and if it dosent work you have to tear grind and sand and redo it with epoxy !! so why waste your time .

I have been seeing these things for more than 30 years where some one comes along with a surposed magic wonderful idea of using poly on wood but it never stands the test of time and falls appart .
If you want to see what works and what dosent go and have a look at a yard that does just boat repairs and you will see first hand all the silly ideas that looked good at the time when first done but under pressure just dont work at all .

[barks]

Epoxy would have been the best solution. Poly will work OK until water (typically rainwater) gets into to wood and starts the rot. If you can keep the water out of the wood it will be fine for many years. If you have a poly covered plywood transom with bolt through fixtures then you will this will rot first. There are many boat repair businesses making a living from repairing 30 year old ply and poly transoms. Stringers should be fine.

[pescaloco]

I P.M.'ed Rwatson about the Pro boatbuilder article and he was nice enought to post a link ( Thank You Rwatson )

The origin of this post is that I own a newly constructed 27ft skiff (HULL) that I bought just hull fitted with poly/plywood stingers 2 bulk heads 3/4 ply sheathed with glass and polyester resin.

I think we all know that epoxy is superior to polyester, but was looking for opinions on the value of epoxy overcoting the existing integral wood parts.

Thanks all

[ondarvr]

I see a tremendous number of production, custom and semi custom built boats and I agree epoxy is a much better product to use over wood. But, I also see a huge difference in the skill of the worker.

Production polyester boats are typically built by workers with little training, are not boaters, have no real knowledge of the products, were trained by the guy that was fired last week for doing a bad job and are only looking forward to the weekend. They are also built to a price point. These boats are rarely maintained in the correct way (sitting in the side yard under a tree with no cover for may years at a time with the plug in). Many times the products (wood, resin and glass) used are chosen for the price (lowest), not how well they will do the job. Some of this has changed over the years, but the mass produced boats of the past were notorious for poor quality.

The typical custom builder has a much better crew that has many years of experience, they have boats of their own, are craftsmen and like what they do. Plus the boats are purpose built with a goal of holding up for many years, showing the quality of construction, are purchased by knowledgeable boaters and while cost is still an issue, doing it "right" is a major concern, so the higher cost is not as much of an issue. Products (resin, wood and glass) are chosen for the best performance in each application and then used with care.

This isn't always the case, but more often than not, it is.

If you were to use the same care and attention to detail with polyester that most wood boat builders use with epoxy, polyester would hold up much better. I'm not saying they're equal though.

[pescaloco]

Ondarvr that is a well though analysis it also happens to be how I feel.

The guy that built my hull has been doing so for 32 years and is a highly skilled craftsman.

I like the idea of additional protection from external epoxy sealing, but like it was said a lot of people take terrible care of their boats and that surly contributes greatly to their early demise. They fill with rain water and leaves, or all the hatches are closed up and no under deck ventilation takes place and a constant cycling of hot and cold builds moisture

[alan white]

You can also check out a WoodenBoat article (I don't have time to look it up)from years ago wherein one Ohio man/company who restored old woodie runabouts had sheathed the bottom of over a thousand (planked!) hulls without any failures except possibly after a good number of years. He describes the method, one he stuck to for decades.
Look guys, Epoxy is king. I liken the comparison of epoxy to polyester as similar to a brick house compared to a wooden-shingled one with boards for trim. We all see that in spite of the absolute superiority of brick, most all houses do not use brick. They use materials that are inferior to brick practically every time. We all know this.
If the old-timers came back to life today, most all (who used boats day in and day out) would use polyester resin to sheathe hulls, decks, roofs, and cockpits. Just like the way they used iron fasteners rather than bronze or copper. Why? It was more practical, just like not building with brick. Ultimate longevity and zero maintainence are paid for by a lot of work doing something else---- earning money to do the job.

Are you going to paint those areas anyway? How about an epoxy paint?

[PAR]

Most epoxy paint is actually polyester. Some two part paints are real epoxy, but so diluted with solvents, nothing compared to the laminating resin we're use to. Epoxy paint also tends to chalk up fairly quickly. You're better of with a single part polyurethane or LPU, for durability, gloss, etc. Epoxy paint isn't a substitute for epoxy coating.

Thanks. A product by Devoe maybe?

[pescaloco]

Plan 3 coats epoxy resin as overcoating, and paint (not sure what paint)
But like the 1 part LP idea, nice and easy

Mark that Devoe paint is pretty good I painted an aluminum tower and it held up very well.

Thanks Alan I will see if i can come across the artice you mentioned