CPES......AGAIN....

[lumberdude]

Does CPES actually improve the waterproofness of a boat, or is that the job of the finish coat? I have no rot on my little boat, but I have these nightmares of getting my boat all finished, painted up and looking great, and the first time I put in in the water, it fills up like runnin a water faucet.


lumber

[thechemist]

Hi, Lumberdude...I assume by waterproofness you mean the relative degree of resistance to water diffusion, or maybe how little liquid water is in the bilge, and it really depends on your particular coating systems and construction details. Perhaps if I ramble a bit about the general subject and then you add some specific construction details, soneone will have some specific experiences that relate well enough to your particular situation.....

The first line of defense of any coating system on wood is the outermost coat of whatever. [that oughta be a safe statement......gotta start somewhere....]Below the waterline, this might be an antifouling paint, designed to slowly leach out something to kill, or at least severely stun, small life. These things may have wood, or some epoxy coating, or some resin/glass laminate beneath, and those things have some moisture-diffusion-resistance. By the time one gets down to the actual wood, which may have CPES in or about it, one usually has something on the exterior which has a fair degree of moisture-diffusion-resistance.

On the inside, assuming the interior wood is fairly dry, one has some degree of ventilation, and some degree of ease with which the few molecules of water that DID get through the outer stuff, can be carried away by interior air circulation.

It is the balance between these two degrees of resistance to /encouragement to water diffusion that determines the moisture content of the wood in the middle.

The Gougeon Bros. did a test some years ago where they coated entirely a piece of wood in WEST and soaked it in water for, I disremember what, perhaps some weeks, and it showed negligible weight gain. The same test can be continued for some months and the coated wood weight comes right up as water diffuses, slowly but inexorably, through the coating until the wood is completely waterlogged.

Any product will give that result because there is only one path for the water to get in and no way to get out.

Virtually any product on the outside, and much less of it on the inside, and good enough ventilation on the inside, will give a dry hull. The idea is basically independent of product or wood,

The foregoing applies to plywood, or more-or-less-one-piece-of-wood components. The engineering details of how a boat is made, specifically when composed of separate pieces of wood, generally called planks, is quite a different matter, and the whole issue of how planks are caulked and to what degree they absorb water and swell, is another whole subject, and these are more properly engineering than chemical subjects or coating-system questions, and I will not take those up here, for they are pretty well addressed in the archives of WBF.

Coating longevity may be affected by CPES on the wood, but there are a lot of more important factors in determining how dry the hull is.

[PugetSound]

"I have no rot on my little boat, but I have these nightmares of getting my boat all finished, painted up and looking great, and the first time I put in in the water, it fills up like runnin a water faucet."

OK, well, I think that there is really nothing technical I can add to the answer given by the Chemist so I will instead address the psychological factor. I think that every boatbuilder entertains fears of putting the product of all that effort into the water only to find that it isn't working out -or worse, leaking like a sieve. The answer to your nightmares is that you read/reread Farley Mowat's book "The Boat Who Wouldn't Float". I promise that this book will at least make your nightmares more enjoyable. http://media5.hypernet.com/~dick/ubb/smile.gif

[This message has been edited by PugetSound (edited 10-27-2001).]

[dasboat]

Listen to those guys dude.
From what I can gather , you take great care to ask lots of good questions and then proceed to do things correctly.
Trust that!

You know your attn.to detail,and your willingness to research before you act.
I'll bet that little boat turns out to be a beauty that will float for a long time.
Darryl

[lumberdude]

Thanks guys, and Darryl, you always know how to make a guy feel better. The boat is coming along pretty well. Everything is sanded, inside and out, I've started staining. I decided to stain, to even out the wood, and I know some would think staining is a no-no, but it actually is looking very nice, and that's the way I want it to look.

I'm starting to get excited with the new look of the boat and everyone that comes by to see it loves it. There aren't very many wood boats in this area.

Oh, another question I have is, the classic valspar spar varnish, is it okay to use or are there more expensive or better brands to use. What is the differences in varnish? After the staining is completed, I'm going to work on a "dust free" area in my garage and start tackleing the inside of the boat.

Oh by the way, Charlie S. I won't be needing the penn-yann stain. Thanks for the offer, but I had some stain of my own and decided to break from tradition and "do my own thing". I will still need lots of advice though (obviously), as I still don't feel I know much of what I'm doing.

I had an opportunity on my vacation to go down to a local lake and check out some big old wooden cruisers. They were fantastic! I've never really checked out the bigger stuff and I think I'm hooked on a future bigger project. There seem to be some "good deals" down there and quite a few fixer uppers that won't need a total rehaul. It's funny that the more I get in to wooden boats, the less attractive the fib******* ones look.

Thanks again all...

Lumber

[ken mcclure]

Hee-hee!!!! Another convert!

Where's the pics, dude? Your project's starting to get exciting!

[dasboat]

HEH HEH HEH,I'm with you KW.
The second I read Dude's "good deal" remark,I just chuckled and thought "oh oh",another one bites the dust. http://media5.hypernet.com/~dick/ubb/biggrin.gif

[lumberdude]

Isn't it a "good deal" when they are still floating??

Of course, take away the bilge pump and that's another story.....

[paul oman]

Everytime CPES comes up I get myself in trouble! Anyway, the the use of any penetrating epoxy or use of solvents doesn't belong here. My spin would be to use a 100% solids epoxy (i.e. solvent free) over the hull because with 100% solids products wet film thickness equals dry fill thickness so if you fill in a crack or leak with the epoxy it will stay filled as the epoxy hardens. "Regular" paints etc will lose up to half or more of their volume as the water or solvents go into the air - usually reopening the crack....

Most epoxies are rather brittle and will not expand or contract the way wood will. It might sometimes be a problem, however epoxies with elongations of 25% (or even 40%!) are available. Actually the best fix it to use the epoxy inside and out - completely encasing the wood instead of just coating (and restricting its expansion) on just one face.

I hope this time I haven't said anything that really upsets any of you!


Paul Oman progressive epoxy polymers
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[Art Read]

Well, Paul... If by "having no place here" you mean in the "WoodenBoat Forum", I'd say, "well... it all jus' really depends on how you peel your shrimp... "Total encapsulation" certainly sounds logical and is a noble pursuit with some construction methods, but using just a slap of CPES on a "timber built" boat, before fitting faying surfaces together or as a prep for finish work has a lot of reasons to be "included" here. Keeping water "out" ain't one of 'em. Ain't supposed to be. Keeping rot from getting a head start? Could be. We'll see. Getting a finish to stick better, go on easier and last longer? Yup. But using it in hopes to keep leaks away, by itself, Nope.

[This message has been edited by Art Read (edited 10-28-2001).]

[thechemist]

Originally posted by paul oman:

Everytime CPES comes up I get myself in trouble! <snip>

Keep trying.....you will eventually work out how to not get yourself in trouble.



Originally posted by paul oman:

<snip>My spin would be to use a 100% solids epoxy (i.e. solvent free) over the hull because with 100% solids products wet film thickness equals dry fill thickness so if you fill in a crack or leak with the epoxy it will stay filled as the epoxy hardens. <snip>


I think you will find that epoxy-coating the exterior of a planked boat will cause the customer to use a lot of epoxy, but wherever that epoxy coating bridges over between two separate planks there will be a high probability of cracks appearing, because wooden planked boats tend to "work" as they are sailed.... same is true of antique or classic power boats......and putting a layer of epoxy over the hull will create mechanical discontinuities where the epoxy-wood interface exists......between separate pieces of wood......wood being physically weak in shear and thus tending to split easily. Below the waterline water can leak in at these cracks that tend to follow seam lines, and spots of rot eventually develop.

A way around this is to lay up enough glass/kevlar/whatever fiber over the external surface as to have an outer fiber-reinforced shell that is stronger than the internal planks, and thus determines hull mechanical properties.

The percentage elongation of a coating resin that might allow caulked seams to work appropriately is more on the order of a hundred percent or more, which is why elastomeric sealants are used in seams, and often low-modulus ones at that, since joint movement is not a predictable thing and some spots may move more than others, depending on the particular vessel and sailing conditions.

The use of epoxy on planked boats was popularized by the Gougeons 20-30 years ago, along with such practices as gluing wood splines into all the seams of a planked boat and coating the outside with WEST......some have called such construction a "West Bottom", but Gougeon, inc., objects to this use of their trademark "West System".

This is a kind of mechanical design heavily promoted by an epoxy manufacturer, with the purpose of maximizing consumption of their product by the general public, regardless of the mechanical validity of the idea. The products of such manufacturers have appropriate uses, and inappropriate uses.



Originally posted by paul oman:

I hope this time I haven't said anything that really upsets any of you!


Paul Oman progressive epoxy polymers
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[ford]

a question for the "chemist"
if water vapour can pass through an epoxy barrier, then coating the interior of a sheathed yacht, just how much or little epoxy coating would be sufficient to still allow the vapour to pass through to maintain the equilibrium and yet keep water from wet sails or whatever out?

[thechemist]

This is not a trivial question, and there is no simple answer. Consider your exact circumstance. Look again at the concept of the greater moisture-diffusion-barrier needing to be on the outside, between the wood and the water, and think VENTILATION .

[swingking]

From what I have read, the plywood glue line is a very good water barrier.
How well does water vapor pass thru the glue line? Has any testing been done?

Thanks
Mat

[thechemist]

I had not noticed this last post to this thread...my apologies if swingking thought the question was being directed to me......if not, then what-the-heck, as long as I am here I may as well say something.


Um.....errrrrr.....unh.....you know, I don't know of any specific testing that has been done of that. Lemme go measure the glue-line thickness of a random piece of Fir plywood:

<interlude>

Back, now....I rooted around in the sawdust and debris around the table-saw and found a piece of fairly decent quarter-inch, a bit of T-111 [half-inch crap] and a bit of 9-ply half-inch spruce. Microscopic examination at 25 X magnification, with a callibrated reticle, shows me that the typical glue line varies from a tenth of a millimeter to literally zero, and it varies back-and-forth A LOT. The T-111 had frequent air gaps in the glue line, while the others were fairly good in that regard. All had glue-line thicknesses that were zero more often than they were a hundred microns [.004"].

At a guess, the average glue-line thickness might be twenty to thirty microns, but the irregularities in compressiblity of the wood fiber bundles from one millimeter to the next force the film thickness to essentially zero, frequently.

What I would say is that a glue-line in plywood is of neither consistent thickness, nor of consistent integrity, and I would not expect them to offer any reliable barrier to moisture diffusion.

[swingking]

Thanks Chemist for your response, it is always interesting to get your ideas.
I assume from your posts that you would not epoxy coat the inside a ply boat.
I agree with this even if this would go against conventional practice:

Kern Hendricks, System 3 Resins:
"Professional builders like Sam Devlin epoxy/glass the outside and epoxy coat
the inside of plywood boats. He (and other professionals building plywood boats) have been doing it this way for over twenty years with excellent results."

Jacques Merten, ply boat designer says:
"always encapsulate the wood (plywood), two sides."

West Epoxy also goes for encapsulation.

I have been rethinking my stand depending on the properties of the ply's glue line.

From Dave Carnell tests at:
"Glue lines of both plywoods are significant moisture barriers."
http://groups.google.com/groups?hl=en&rnum=1&selm=3703DFEB.689914A6%40worldnet.att.net

If glue lines are significant moisture barriers it would seem to restrict the transfer of water from boat exterior to interior and make encapsulation more attractive?

Comments

Mat

[Art Read]

Consider the source. "Conventional wisdom" or savy marketing? Just a thought.

[thechemist]

swingking, you are misquoting an "experimental report" that is in itself suspect. Note, just for example, that the epoxy used is reported in all these pieces at .01682 gallons per square foot, and they ALL had that EXACT same amount. I don't believe it could be done by anyone.

This is FOUR significant figures, and NO ONE spreads googe of any kind with that degree of acuracy. Thus, the actual epoxy coating thickness is unknown. If a preweighed quantity of epoxy was used, and used up on each piece, I doubt that, as "three coats" were reported, thus without a wet film thickness gauge the thickness of a "coat" is unknown. Normally, when doing these sort of tests one makes many specimens of each, and averages the results, so as to eliminate the variables of testing only one of anything. The report says "samples" implying more than one, but no statistical data given. Bad science.

Further, as anyone who has spread ANY brand of liquid epoxy on wood has seen , different kinds of wood absorb the stuff .....ANY stuff.......differently. It is plausible to expect that fir and luan would be wetted to different degrees, and perhaps one or the other had a more effective moisture diffusion barrier.

Further, note that these experiments were conducted over quite some time, and show the rate of moisture diffusion into a closed environment. Eventually, it all gets inside fully encapsulated wood. Different rates, same fact.

This does not represent the real world, where the barrier is on the outside only.

What that experiment proves is that fully encapsulated wood, left in the water, will eventually reach the fiber-saturation-point. That is all it proves. Whether that is a good thing or a bad thing is the subject of a separate discussion.

I am not saying not to do SOMETHING with plywood. I am saying that the experiment is not what it seems to be, and offers a conclusion that does not follow from the data.

To quote Mr. Carnell's own preface from the google you cite, Epoxy-coated plywood absorbs much less water than epoxy-coated wood; apparently the glue lines of the plywood are significant barriers slowing water absorption. and notice what he actually said......and compare that with the fact that he tested two different kinds of plywood, fir and luan....and no "wood", presumably meaning separate planks.


If you put a moisture barrier on inside and outside, both, you create a situation where the wood will be highly humidified, and will rot quickly once the epoxy coating suffers some mechanical damage, such that a crack or check or something similar happens. If there is no damage whatsoever, and further the construction is with many small pieces of wood, there are many epoxy barriers and rot does not readily spread. This discussion came up recently in another thread....

http://media5.hypernet.com/~dick/ubb/Forum1/HTML/001435.html

and if you go look THERE you will find out why Dave Carnell said "than wood" and it was because he was referring to his own tests in comparison to the OTHER tests which were reported in the instant reference, not the earlier one where he quotes himself out of context. See how data mutates?

Anyway, look at the actual data, comparing plywood with pieces of wood. I did this, too, and what I observed was that the wood absorbed relatively little, and then suddenly absorbed a LOT. I attributed this to the expansion of the wood with increasing moisture content, finally exceeding the elasticity of the epoxy [I used WEST] and cracking the epoxy coating, allowing rapid water absorption. This tends not to happen with plywood due to the perpendicular orientation of layers of wood fibers, thus if the outer plies have a strong bond to the core ply one might not see the outer plies expanding enough to crack the epoxy coating. Further, if the outer ply was effectively saturated, little change in dimension of the outer ply with water absorption would be possible, and in fact the cellulose fibers might not absorb as much water due to their surface hydroxyl groups being tied up with the cured epoxy resin.

What all that means is that an epoxy coating on the outside of a sheet of plywood ought not to penetrate much of the outer ply if it is to be evaluated as a moisture diffusion barrier. I have nothing against doing this sort of thing, or doing this sort of experiment, but I do not like the way it was done and the tempting conclusions one rushes to draw from it.

If the experiment were to be done such that scientifically valid conclusions could be drawn from it, it would be done in the following manner:

Use some number of samples. The probable error of N samples is (square root of)N. Thus, use maybe ten, preferably thirty. Show the statistical spread of data as well as the mean.

Use square pieces, not 3 x 10, so the fiber length is the same in both directions, avoiding some unknown effect of wood fibers only in one direction doing something. Wood is a highly anisotropic material [means different properties in different directions].

Use plywood of MANY [eight to fifteen] plies, so surface effects do not influence bulk effects.

Now, having said all that, does this experiment measure diffusion resistance of water by glue lines? I think not, with this experimental construction. One would actually want water on one side only, and free air and a means of measuring vapor transport through the plywood.

This experiment measures water absorption into whatever ply is available to accept it. It could just as easily be that the outer ply, if coated but not saturated, went quickly to the FSP and the core stayed dry, or it could be that the water went evenly through the entire piece, and there is no way to tell which barrier is doing what.

Fir plywood with three equal plies absorbs water faster than luan with two thin outer plies. Why?

Maybe the epoxy wet the luan better than fir. Maybe the epoxy lay on the fir surface and it cracked, allowing faster water absorption. The experimental design needs to be different in order to draw the conclusion that was offered.



[This message has been edited by thechemist (edited 11-05-2001).]