Re: Lightweight marine ply
- I suspect what you are saying is correct. Epoxy coating is not the be-all-end-all. However, monkey see monkey do, so I will sheathe and coat my AS29. But I will use a local epoxy that costs 40% of WEST. Is this false economy? I don't know. What does everyone else think?
--- In email@example.com, "c.ruzer" <c.ruzer@...> wrote:
> --- In firstname.lastname@example.org, "Eric" <eric14850@> wrote:
> > Whatever reference I had in mind I cannot find. I thought it was
> > from The Gougeon Brothers On Boat Construction, but do not have
> > time to read the whole thing. I've done research on line and what
> > I have found seems to indicate that Epoxy has much better
> > resistance to moisture penetration than other options.
> You will note that I have not mentioned epoxy encapsulation; i.e., coating both sides of everything with several coats of epoxy resin. It has no advantages and is a waste of money and time that adds useless weight. It won't turn lauan underlayment into marine plywood, though it will make it cost nearly as much. It does not keep the water out of the wood boat that lives in the water and a dry sailed boat doesn't need it." http://www.angelfire.com/nc3/davecarnell/epoxy.html
> "A modern myth is that epoxy resin penetrates sound wood and that epoxy coating prevents water from being absorbed by wood." " Boats are immersed in water, so I measured water absorption while immersed of ¾" pine coated with three heavy coats of epoxy resin. These coatings were about twice as thick as used at FPL. In fact, their total weight was a little over 30% of the weight of the uncoated wood. Immersed in water they absorbed 20% by weight of water in 200 days. That is the water content required to sustain rot organisms. There are two other requirements for rot to occur-presence of the organisms and oxygen to sustain them. The rot spores are astronomically larger than water molecules, so if the wood did not have them to begin with, epoxy coating would likely keep them out. As to oxygen, the oxygen molecules are far larger than water molecules and do not have the unique properties of water molecules that make them capable of penetrating any organic material-natural or synthetic. I learned this the hard way while supervising spending a couple of million dollars around 1960 on a DuPont research project to make building products and pipes of resins reinforced with kraft paper. Dry kraft paper is a pretty strong, stiff material; wet, it is like the proverbial dishrag. The chemists doing the experiments tried every polymerizable mix they could conceive, including epoxy resins, to make products that wouldn't lose their stiffness in long-term contact with water. The research director held his head in his hands when I reported that we had had zero success. I also coated exterior fir plywood (three equal thickness plies) and underlayment lauan plywood (thin skins and thick core) with about 30% of their weights of epoxy resin. The fir plywood took about 1½ years of soaking to reach 20% water absorptiion, but the lauan hadn't reached that point in two years and looked as if it never might. This resuly hints that the glue lines between skins and cores of plywood are quite effective barriers to water absorption. David W. Carnell 11 March 2004" http://www.angelfire.com/nc3/davecarnell/articles.html
- I've placed a scan of "water resistance of epoxy coatings" a
test results article, in Jan/Feb/Mar 2012 Australian Amateur Boatbuilder #76, pp7&8, by Dr Bruce McConkey, Boatcraft Pacific, in the BOATBUILDING folder in group Files:
http://groups.yahoo.com/group/bolger/files/BOATBUILDING/ (Seems similar to the tests Dr Dave Carnell conducted.)
Dr McConkey's article authoritatively advises on what type of epoxy coating, thinners & etc. Does it mean ENCAPSULATION or just one side though?
Sheathing counteracts checking and or abraision if that's a likely issue with the material or location... A good paint system alone is often advised for unwetted, low wear areas... or all over for light, dry-sailed boats.
--- In email@example.com, "sandidgeneal" <nsandidge@...> wrote:
> I suspect what you are saying is correct. Epoxy coating is not the be-all-end-all. However, monkey see monkey do, so I will sheathe and coat my AS29. But I will use a local epoxy that costs 40% of WEST. Is this false economy? I don't know. What does everyone else think?