View Full Version : Penetrating Epoxy Sealer

Dave Carnell
08-13-2001, 11:23 AM
Here are some Gougeon data on water absorption through epoxy. They
concluded that penetrating epoxy (CPES?) is useless at keeping out

Data from Gougeonís Epoxyworks, Number 14, Fall 1999, p. 16:

Water absorption after six weeks exposure at 100% RH.

4 coats penetrating epoxy: 33.66% by weight moisture uptake

3 coats West 105/205: 7.57% by wt.

2 coats pen. epoxy + 3 coats 105/205: 7.24%
(2 hr. between coats)

4 coats 105/205: 5.76% by wt.

2 coats pen. epoxy + 3 coats 105/205 5.69

7 coats 105/205: 3.43% by wt.

The extremely high water absorption by the wood coated only with penetrating sealer (CPES?) can be explained by the fact that evaporating the 70% or so solvent leaves only a sponge of epoxy resin. The water absorption through the West system epoxy resins confirms my data and conclusion that epoxy doesn't keep water out; it just slows the penetration.

Art Read
08-13-2001, 11:32 AM
That's why those of us using it on "traditional" construction use it for better paint/varnish adhesion without altering the swelling properties of the wood. Anybody who hopes this product alone will "encapsulate" their wood will be dissapointed. Still wonder whether or not it does anything as a wood "preservative" under there... 'Till I see for myself, I guess I'll keep on using it in combination with good, old red lead primer.

[This message has been edited by Art Read (edited 08-13-2001).]

Ian McColgin
08-13-2001, 11:49 AM
The test is a little misleading - & I use WEST.

Smith's is not thinned with solvents. "Penetrating" epoxies that are simply thinned are indeed silly but have little to do with CPES.

Further, CPES is not meant to be used alone. It's an undercoat sealer.

Far as that goes, epoxy is not a very good top coat in the best of circumstances.

This is about as stupid a comparision as the counter against WEST based on pouring some mixed epoxy on a sheet of wax paper, noting how brittle the resultant cured puddle is, and claiming that for that reason it's a bad glue for wood.

One wishes that these guys could be a little less self-serving.

08-13-2001, 12:43 PM
CPES, the "ferrocement boat" of the New Millennium.

Doug Wilde

08-13-2001, 02:34 PM
Ian - I hate to disagree but CPES does contain solvents:

"The product (CPES) is a 50:50 two-part epoxy formula that is carried into wood by a powerful solvent mixture."

This was found on:


Adam C
08-13-2001, 04:34 PM
So what's the angle here...is anyone out to knock CPES?

I really wonder whether the detractors of CPES have actually ever used it? Perhaps their head is too fully lodged in their ass to examine it for themselves, not just on paper.

I am not affiliated with CPES or Smith, obviously. But I do have a wood boat with extensive dry rot and have seen it do miraculous things. I am truly impressed with the product. Try it and you'll see, no BS. I can show you wood that was mildly dry rotted on my boat that CPES was applied on. It feels firm and solid now, like new wood.

Again, I don't want to plug a product that doesn't work, but Smith's does. beats the hell out of Antifreeze, where I know Carnell is going with this thread.

My 2c. Adam

Mike Field
08-13-2001, 08:22 PM
As I see it, Adam, and without regard to whatever attributes CPES may possess, then if you had a rotten boat you've still got a rotten boat. I imagine that CPES treatment would have stopped the rot progressing, by encapsulating and isolating the spores. (In a similar way, ehtylene glycol would have also stopped the rot progressing, by killing the spores outright.) But unless it's literally magic stuff, CPES can't have transformed the rotten wood back into sound timber.

And, with respect, unless you yourself have magic powers not vouchsafed to the rest of us, you might suspect where Dave Carnell "is going with this thread" (if, indeed, he was going anywhere with it,) but you can hardly know it.

I haven't had occasion yet to use either CPES or ethylene glycol treatment, so I'm keeping an open mind on both. I don't think arguments for or against either carry much weight without any evidence. In his posting, Dave presented some evidence, and has therefore added a little to the body of knowledge we share about this material. How sound the evidence is, or how relevant, we need to decide for ourselves.

[This message has been edited by Mike Field (edited 08-14-2001).]

Bob Cleek
08-13-2001, 08:37 PM
CPES is a SEALER. Claims that it restores rotten wood, must be tempered by an understanding that in that capacity it's abilities are limited. The mistaken belief that CPES creates some sort of waterPROOF barrier is widespread. As noted above, it is permeable and only waterREPELLENT, which is preferable in wooden boat building applications. I would urge anyone who is still "on the fence" about using this stuff to read Smith's literature (not the Rotdoctor site) at http://www.smithandcompany.org/ and draw your own conclusions. I've used gallons of it as a sealing primer under paint and it is fantastic in that application. I can't say I've used it ever to "restore" a rotten hunk of wood. If it is good enough to be used by the 55 gallon drum by the GSA and the Navy, who am I to quibble! LOL

Ian McColgin
08-14-2001, 08:36 AM
Back to the solvent issue - I don't take the RotDoctor as gospel about too very much. Smith told me that the volitile stuff is a volitile integral component, not a solvent. I'm not sure I truely understand the distinction since we use 'solvent' both to mean individual often volitile components and to mean something you might add to the mix to dilute, speed drying or whatever. If we restrict 'solvent' to the latter sense, CPES does not have it and the WEST tests were done with glues that had been thinned. I find a world of difference between something designed from the getgo as a sealer and a glue thinned out to imitate a sealer. In point of fact, Smith also makes a glue that is differently formulated than his CPES.

All these carbonbased non-life forms have some family similarities but the fact remains that CPES is a nifty sealer and thinned WEST is not.

Keith Wilson
08-14-2001, 09:09 AM
One piece of data missing from the data in Dave Carnell's initial post - How much water does untreated wood absorb? Gotta have that control. And was that Smith's CPES or something else?

I think the bit about solvents is a little misleading. Of course CPES is solvent-thinned epoxy. They specifically say you should wait to paint over it until the solvents have evaporated and it doesn't stink anymore. However, it's designed to be used that way, unlike WEST epoxy mixed with acetone, for example.

I have no idea how well it prevents water absorbtion, but it does seem to form a dandy tie coat between the wood and whatever finish goes over it. That alone is enough to get me to use it. OTOH, maybe we just think that anything that smells that bad MUST be good! http://media5.hypernet.com/~dick/ubb/wink.gif

08-14-2001, 10:24 AM
Ian - In a paper written by Steve Smith "Restoration of Rotted Wood with a Flexible Penetrating Resin"
at http://www.woodrestoration.com./ Section IV

8.6 Product Description from the Manufacturer

"This permits the Solvent-Resin mix (CPES) to penetrate the natural porosity of the wood."

Anyone care to share MSDS?


08-14-2001, 12:02 PM

I just emailed Smith and got this:

The main solvents in the CPES are Toluene, Xylene and Isopropyl Alcohol. Not good for drinking. Take care,

Guy Prince
Smith & Co.

Ian McColgin
08-14-2001, 01:11 PM
Got it. That's why I mainline rather than drink it . . .

08-14-2001, 01:49 PM
Note that Gougeon has constructed a test which shows a dramatic difference in some property between their product and their competitor's. Anyone favoring or disfavoring one company or another can use such data as evidence of something being better or worse.

This easily becomes the Argument by False Analogy that we occasionally play with, or fail to recognize.

Referencing What the Product May Actually Do by actual test or testimony of users is the most valid thing one can say about any product.

The fact that a product does some task poorly does not mean it is a bad product, be it West, CPES, antifreeze or any other. Each product does some things better than any other. Put West or CPES in your car radiator and you will be in big trouble, for antifreeze is the best of those as an engine coolant.

Where firefights can start is where a manufacturer or their representative promotes a product for a use which is not appropriate, which does more harm than good, or just plain does not work very well.

The test of water-barrier-properties of West's properties versus Smith's CPES is not a valid one because that does not seem to be the primary purpose of that product, meaning the two products do not share a common purpose.

From Smith's company web site, http://www.smithandcompany.org

"The original Clear Penetrating Epoxy Sealerô was ...... [developed for restoration of wood in the marine marketplace,]... the highly aggressive marine conditions proved the acid test for this new technology. It gave paint and varnish that actually stuck, and sealants and adhesives that did not tear or crack where all other products readily failed. Some boat owners were also painting contractors, architects or similar, and began to use these products in the architectural field, for restoration as well as an adhesion-promoting primer for paint on new wood buildings. It proved far more workable than any other practice for "restoration" of deteriorated wood, and it soon became apparent that enamel or latex house paints applied to wood treated with this product did not readily fail, where without this treatment failure of paints typically occurred in half the time and rot soon started up again behind a wood repair with a filler. "

This does not seem to be an intentional application area of Gougeon's products , from what I have seen of their literature.

Further, from page two of that web site, http://www.smithandcompany.org/more.htm

"The new technology departs from old wood treatment practices, even with epoxy products, with the discovery that the fungi that cause decay in wood actually penetrate into wood far beyond the visible region of total decay, and that the extent of this penetration is not obvious and may be many inches. The old-technology practice of removing visibly decayed wood leaves an infected region below the "repair" and any water intrusion or diffusion that brings the humidity above roughly fifteen percent triggers germination of fungal spores in the infected region, and rot begins anew.

The genesis of the new technology was the development of a product that would selectively impregnate the entire infected region of wood with a water-repellent resin system derived in large part originally from wood, to bring about restored mechanical properties similar to wood and a water-repellent characteristic, while leaving a natural porosity in the treated wood so it could "breathe" as does natural wood. This prevents the accumulation or condensation of liquid water in the wood behind old-technology filler repairs, a leading cause of failure of such repairs. "

It should be clear that one manufacturer is promoting a product for one purpose while another manufacturer is testing it for a different purpose, finding it lacking, and drawing a [false] conclusion.

As for a real water barrier, from that same site,

"In about 1975 Steve Smith discovered what caused the gelcoat blisters and laminate decomposition that was suddenly prevalent on glass-reinforced polyester (GRP) boats ("fiberglass" boats). He invented then the barrier-coat technology which is now in common use everywhere in the world for the repair of such damage and prevention of its occurrence.

That same barrier coating, when applied to the bottom of a wood boat, made possible the end result of a wood boat with a dry bilge, normally an unheard-of condition. Two additional factors were vital in achieving that result. One was the caulking of every seam and joint with a flexible, high-adhesion sealant. This absorbed small relative movements while maintaining a water tight seal. The second was the use of Clear Penetrating Epoxy Sealer, which allowed these products to adhere to the wood, whether dry or slightly damp."

If Gougeon were interested in comparing a moisture-diffusion barrier of their own with one of Smith's, or Interlux's or anyone else who makes such products , they could have done so directly, as most paint manufacturers, even Smith, make such things. To my knowledge no one has done direct comparisions of these products, although I expect the mineral-filled paints will do better than the unfilled resin coatings.

In any test of completely sealed wood samples, measuring weight gain, one may still not be measuring what is useful in the real world, as all will ultimately reach equilibrium as fully saturated specimens.

Where coatings are applied to wood hulls, it is the water-evaporation-rate off the inner surface, balanced against the water-diffusion-rate through whatever barrier coating, if anything, which may be on the outside, which determines equilibrium moisture content in the wood.

If the inner water evaporation rate is high enough, any external coating [or antifouling paint alone, if perhaps ten years build-up] will give wood with moisture below perhaps 15-20%. If the inner water-evaporation-rate is low enough, the best external water barrier will be inadequate, and the wood hull will eventually be fully waterlogged, with a moisture content far beyond the fiber-saturation-point.

Dave Carnell
08-15-2001, 06:17 AM
At the moment I have misplaced my MSDS sheet for CPES, but I'll find it. Interestingly, it does not include epoxy resin or hardener as ingredients. When I queried Smith on this I was told the concentration was so low it doesn't have to be listed. The MSDS sheet lists 17 solvents, each at "less than 50%". This is a legally proper obfuscation of the true content. The information that it is isopropyl alcohol and aromatic hydrocarbons fits my observations in my prehistoric lab. The manufacturer claims water-soluble solvents make it penetrate farther. This is true to some extent, but the water encountered will make the epoxy insoluble and separate, just as it does when I titrate it with water. Uncoated wood would absorb in the 35-50% range of water. My uncoated plywood sailing skiff went from 107# as built to 150# in six months of living in the water on Pages Creek. Sure noticed the difference when I cartopped it.

08-15-2001, 10:32 AM
What's your point, Dave? Nitpicking the MSDS for the product does not seem to have any direct connection with your original post of the Gougeon's bogus experiment. Do you have some disagreement with how manufacturers generally put their MSDSses together?

Keith Wilson
08-15-2001, 12:09 PM
All right gentlemen, and particularly Mr. Carnell, what's the point here? That CPES is useless snake oil? OK, let's look at this rationally. Here is a starting point for further discussion by those who know more about this than I do. What does Mr. Smith claim that it does? I quote from the paper at http://www.woodrestoration.com/:

"Product description from the manufacturer:

The Professional Version of Clear Penetrating Epoxy Sealer is designed to dissolve not only the saps and oils in the wood but also the natural water, and to keep the impregnating resin dissolved ("in solution") in the presence of those saps, oils and moisture of the wood. This permits the solvent-resin mix to efficiently penetrate the natural porosity of the wood. Fungi and bacteria produce an additional porosity that is especially penetrable by this product.

The resin system is formulated primarily with resins derived from wood and therefore the resin system is compatible with the chemistry of wood in a way that no other resin system is. The resin system is very hydrophobic to inhibit liquid water accumulation in impregnated regions while allowing (via the designed porosity remaining in the wood) the diffusion of water vapor through the impregnated region as well as the natural porosity of the wood. Wood impregnated with this system has a toughness and flexibility comparable to the original wood, because the resin system itself has a toughness and a flexibility comparable to the original wood.

When fungi and bacteria eat their way into wood, they destroy the material and create porosity on a gradient between the sound wood, the slightly porous wood with fungal spores in that region but the wood apparently sound, and then more obviously deteriorated wood, until at the extreme there is wood so porous and so obviously deteriorated you could stick your finger into it. When wood is impregnated with this material, the penetration extends all the way through the zone of deteriorated wood containing bacterial and fungal spores, and on into any available porosity of the sound wood. This impregnation helps the wood resist further deterioration such as might be caused by fungi or bacteria.

Because the primary purpose of the product is not to kill fungi or bacteria or encapsulate fungal spores in epoxy, thus possibly stopping them from hatching, (even though it might do that) the Federal EPA and the California EPA (Environmental Protection Agency) do not allow such claims to be made unless the product is registered as a pesticide. Since the primary purpose of the product is the mechanical restoration of deteriorated wood, the product is not registered as a pesticide. Consequently no such claims are made by the manufacturer and others are discouraged from making such claims.

The sole claim for this product is that it can improve the physical properties of wood in some circumstances, and that it can help the wood resist further deterioration such as might be caused by fungi, bacteria, etc. Contributing to this claim is the fact that varnish, oil-base enamel paint and most latex paints stick better and last longer when applied to wood that has been treated first with Smith & Co. Clear Penetrating Epoxy Sealer. This has been a consistent observation by thousands of Smith & Co. customers, since 1972. Improving coating adhesion directly helps the wood resist decay."

So, the following claims, to summarize:

1) When used on rot-damaged wood, it will make it stronger.

2. It will reduce the likelihood of further fungus growth.

3) It will make paint or varnish last longer.

4) There is also a "non-claim" that it may kill rot fungus or spores, or prevent them from growing, as a part of #2. They don't really claim this, because the stuff would then have to be licenced as a pesticide, but they imply it strongly.

I think we can dismiss the business about "wood-derived resins" as advertising. However, this has nothing at all to do with the validity of the claims made.

I use CPES as a primer under paint and varnish, because, in my experience, it appears to make the finish stay on longer, and there are a lot of things I'd rather do than sand and varnish. If it may help prevent rot, so much the better. It's not a cure-all, (and I sure as hell don't put it in my tea) but it seeems useful for this limited purpose.

[This message has been edited by Keith Wilson (edited 08-15-2001).]

08-15-2001, 02:54 PM
Keith Wilson says:
"I think we can dismiss the business about "wood-derived resins" as advertising.
However, this has nothing at all to do with the validity of the claims made."

I would not agree with this statement, "The Chemist" has explained this in previous posts
but have not been able to locate it, maybe he could find it.


Keith Wilson
08-15-2001, 03:59 PM
Which part do you disagree with? That the paragraph about "wood derived resins" is mainly advertising? Or that if the stuff works, it doesn't matter where the raw materials come from?

I couldn't find the chemist's previous post on this; if you know where it is I'd be most interested in reading it.

Alan Peck
08-15-2001, 08:29 PM
I sure hate to weigh in on this one as there seems to be a lot of opinions on both sides. I have tried CPES and it seems to be a great initial coating for epoxy glue.
I am building the boat outdoors under a rainproof cover, However, in really bad rains, blowing wind tends to coat the boat with a fine water mist. I have noticed that the wood that has no CPES is fine, but that the wood that has CPES on it (with no topcoat yet) is starting to be covered with black mold. I don't know what it means, but it seems to question the ability of CPES to inhibit fungus?

08-15-2001, 08:33 PM
maybe you mean this....


wherein I said, at one point,

posted 12-21-2000 09:25 PM
Er......guys......some epoxy does grow on trees....sort of.
Epoxy resin such as you are familiar with is a petrochemical-based product, although it did come from trees, although long dead.

The "epoxy" of epoxy resin and the "resin" part are two different parts. The epoxy part is two carbon atoms and an oxygen atom in a ring. The resin part can be any sort of petrochemical poo or biodegradeable organic goo. Put them together and what have you got? Stickety glippety gloppety goo. Only that takes too long to say which is why we made life easier for you guys and gave you the simple name of epoxy resin. It ain't technically precise, so you can't be too literal with it. It's a generality.

The amine curing agents do come from natural gas, petroleum, and ammonia.

There are a host of resins and oils derived from natural sources, such as walnuts, cashew nut shells, walnut shells or walnuts, tung berries, linseed oil, castor oil, and various oils, and gums from trees, menhadden oil from some sort of fish thing, animal oils, and probably they will even find some sort of oil in something else one day. All of these things can be modified with a few simple chemicals to add an epoxide group or an amine group to them.

When that is done, you have (either before or after curing, depending on your nomenclatural preferences) epoxy from trees. or walnuts. or fish. It can be done.

08-15-2001, 09:06 PM
This was not the post I was thinking about,
I am still looking.


The "curing agents" available in the marketplace vary from petrochemical-derived products to nature-derived products from some oilseeds or nuts to wood to other things. there are various accelerators which make these things cure better under adverse weather or temperature conditions, and some of them degrade or enhance various properties such as water stability, adhesion in the presence of water, flexural or tensile properties, or their ability to promote adhesion of one thing to another.

08-16-2001, 12:21 AM
More on The Chemists point that epoxy is really varied. Some epoxies are water soluable after cure though you won't see them in a boatbuilding material catalog.

Hundreds of epoxy compounds exist. Many more are possible, only waiting for a market so they would be profitable to manufacture. There are even specialty companies that formulate custom hardeners to order for specific needs though this business is smaller now than a few years ago.

The point is, you really need a lot of information to characterize an epoxy system. If not, you run the risk of missing a key element. Further, even the most honest and best intentioned epoxy formulator may unwittingly give you an epoxy system with a major flaw in it unless he absolutly and completely understands your application.

To be sure about the epoxy products you buy, use a reputable formulator that understands boatbuilding. Follow the manufacturers instructions for use explicitly or contact him for instructions specific to your needs.

08-16-2001, 12:41 AM
Seems to me that this thread has strayed a bit. I'll try to recap what I've learned.

There is data that the CPES product is largely solvents.

The original posting contained some data from Gougeons' that solvent-diluted epoxies (presumably CPES among them) don't seal nearly as well as undiluted epoxies.

A reasonable person might expect that a product called Clear Penetrating Epoxy Sealer would actually seal well. Sounds like it doesn't.

If the intended use of CPES is to deeply infuse some pulpy wood with a weak sponge of epoxy, that's a worthy purpose for some users, but not everything I'd want in an undercoat for finish.

Don Z.
08-16-2001, 05:16 PM
Originally posted by JimConlin:
Seems to me that this thread has strayed a bit. I'll try to recap what I've learned.

There is data that the CPES product is largely solvents.

The original posting contained some data from Gougeons' that solvent-diluted epoxies (presumably CPES among them) don't seal nearly as well as undiluted epoxies.

Am I the only person that sees the logic error here?

08-17-2001, 01:53 PM
Sometimes repetition clarifies, especially from different viewpoints.

Spell it out, Don Z.

Georg Moe
08-21-2001, 06:01 AM
There is a possibility that I have missed something here, but...
What most of this discussion boils down to is that CPES is good for the varnish/paint adhesion. But, does it really seal the wood, as its name implies? If the wood was sealed, no water would enter...?
Saturating wood with oil (linseed, Deks++) prevents water to enter, at least in theory I think. But varnish adheres better to a CPES 'saturated' piece of wood than an oil saturated piece of wood. The shrinking/swelling of the wood is structurally not a desired feature (apart from keeping the boat watertight), CPES treated wood is still allowed to do so.
Would a solution be to (almost) saturate the wood with oil, and then use CPES as the final coat before varnish? ...?

:) Georg

Scott Rosen
08-21-2001, 09:16 AM
What in the world is going on in this post?

Smith never claimed that CPES will create a waterproof barrier for wood. The fact that it is water-permeable is exactly why most of us use it. In many applications, it is folly to waterproof only one surface of a piece of wood. If you're going to waterproof something, you want to make it completely waterproof, in other words, encapsulate it. If you coat only one side of a piece of wood with three coats of West, you may still get water under the West from capilary action from the untreated sides, especially endgrain. What will you say then when the West coating begins to lose adhesion? The water may not have gotten in through the West, but unfortunately, it can't get OUT through the West either.

I suggest to the skeptics that you try some CPES as a primer coat for paint or varnish. You've got nothing to lose but a few bucks. Use it on a difficult wood to paint, like teak, and use it on a surface that will get a lot of wear, like a dinghy bottom. What I have found is that the CPES fills the wood grain much faster than any other primer and thereby saves me many coats of primer and many days of work. I can do the CPESing in one day, where the priming used to take several days while I waited for each coat to dry between sandings. What I have also found, and this is the primary benefit for me, is that CPES "glues" the paint or varnish to the wood. It serves as a tie coat between the wood and the paint, and a very effective one at that. I have achieved significantly improved adhesion of my paints by using CPES.

In case you haven't noticed, wooden boat owners spend a lot of time painting and varnishing. CPES is a product that will give your finish work greater durability and longievity and will save you time and work both in the initial application stage and in later stages because the finish will stay stuck to the wood longer.

I haven't used it to restore rotten wood, although I have used it to patch some "soft" spots. (I have rot denial.) It seems to restore strength. I do not know if it will prevent further rot in those spots. Only time will tell.

Another product that will save you much time and work is two-part linear polyurathane paint, like Sterling or Awlgrip. As far as I can tell, of all of the products designed and marketed to make painting and varnishing easier, LPU's and epoxy (including CPES) are the only ones that fit the bill. An exterior LPU paint job over CPES and epoxy could last you over ten years without the need to recoat. One part oil-based paint might last only one year under the same conditions. And one part oil-based paint over CPES might last several years. But under all circumstances, the paint over CPES and epoxy, whether LPU or oil-based, will last much longer than paint applied directly to the bare wood.

Dave--good bait job.

Allen Foote
08-24-2001, 07:04 AM
I don't have 6 weeks to spend waiting for a boat to swell. The final stages of dry rot are what you are "hardening" with the CPES. The fungis spores are in the wood well past the areas you "treated". I'd like to see those areas in another year. lol The U.S. government also buys toilet seats for $800.00 maybe Smith is just jumping on the GSA band wagon. lol

Bob Cleek
08-24-2001, 05:23 PM
I soaked my head seat in CPES and I no longer have to sand the scorch marks off the inside edges!

08-24-2001, 06:57 PM
OH S**T http://www.themelee.com/smilies/s/contrib/geno/rofl.gif
Is it a head or a toilet???

[This message has been edited by dasboat (edited 08-24-2001).]