Clear Penetrating Epoxy

Hello All

Hope you're all having a great weekend !

Has anyone any experience of a product called Clear Penetrating Epoxy Sealant, or CPES, sold by an American company called Smiths ?

Its benefits would appear to be impressive to the point where I am wondering if it's a legitimate product or well-marketed snake-oil ?

Its not cheap and it seemingly has 'nasties' in it which make it so effective -- I'd be very interested to know if anyone on here has any direct experience of it

25 replies:

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RE: Clear Penetrating Epoxy

I had come across this low VOC product when doing another project but did not use it as I still had some regular epoxy resin.  You can read over 100 reviews, with 76% giving it 5 stars.  Let us know what you decide to do.  I think it looks like a good alternative IMO.

RE: Clear Penetrating Epoxy

   Yes, I have used it and it seems to be very effective. I did not try making test panels to leave out in the weather and compare with an untreated panel, but I did paint it on the inside of a boat I was building. I was taking it to an event while in mid build and they were predicting rain. Hence, the CPES coating. I also slathered it on the mahogony gunwhales I had just fashioned to seal them. That was the most impressive part of the boat. Got a lot of compliments on the "oiled wood" finish of the gunwhales and how I achieved it.

 It has very low viscosity, like water, and thus covers a surface quickly. Use this product OUTDOORS or in a VERY well ventilated area! The voc's are more like fiberglass resin vs. epoxy. I suppose this what contributes to the penetrating qualities.

 I was also about to purchase some the other day when I noticed Jamestown Dist. no longer carried it. It seems they are replacing some products with their own line called Total Boat. I ordered a 16/8 oz. kit and just received it. I'm replacing a daggerboard case in my buddy's old dingy and decided to seal up the plywood with a penetrating epoxy, so this product will get a trial run. I'll let u know how the stuff compares if u like. This will happen in the next week or so.


RE: Clear Penetrating Epoxy

I have used their penetrating epoxy on numerous projects from rig shop benches to MDF furniture. It works great.  Unfortunately, it's also liquid gold.  I have given serious thought to using it on all panels below the waterline and on all edges for my Passagemaker build.  It basically makes wood into wood-tone plastic.  This goes well with the marine plywood discussion on another thread, meaning you can use less expensive plywood and make it waterproof.  It does raise the grain a bit when wetted out, so you have a slightly course texture after it cures, but that sands down easily.

RE: Clear Penetrating Epoxy

 @ US $160.00 / gallon I don't see how using it on non-marine ply would be much of a cost savings exercise?

RE: Clear Penetrating Epoxy

With all due respect, that's a loaded argument.  Nobody said anything about needing to buy a gallon.  Penetrating epoxy comes in numerous sizes, down to a kit of just a few ounces.  It's very watery, so a little goes a long way.  For example, a 12oz kit (retail for $43 did my entire picnic table, legs, seats, top, stiffeners, etc.).  I felt that was a very good deal.  A similar kit would be more than enough to do everything below the waterline on any CLC boat, and for $65 you could get the 24oz kit and do both the interior and exterior and all panel edges.  

Also, the use of penetrating epoxy would be a decision that is independent of what type of plywood would be used.  And as stated above, even expensive, marine grade plywood gets wet, swells, delaminates, wicks, etc. so there's nothing magical about it.  I'm just saying that if you're willing to go through the effort and expense of building, invest the time, etc. and you are planning on using one grade of plywood or the other, you should be aware of the pros and cons.  The cost is only one of the many factors to weigh.  Obviously going with higher quality is preferable, but like I said, if I'd only had the marine grade option, I wouldn't have been able to build the boat, have two great summers with my family, and have the satisfaction of building from plans.  Sorry if I derailed this thread, but I think it's an important point.  I knew I was going to catch some flack for it...:)

RE: Clear Penetrating Epoxy

   Cap'nSkully, some great points!

RE: Clear Penetrating Epoxy

No umbrage taken from your reply Cap'n, thanks for the added depth your post adds to the subject. This stuff very well may add value to any project where longevity of the end result is a big part of the endeavor.

My cautions would be where its use might compromise results down the road, as when it's used to 'harden' lesser quality materials that then get coated with other epoxys, where the ultimate bond and mechanical strength is dependent on the epoxy penetrating a substrate that's been made non-porous.

This forum's the best place I know to get experience from others' successes as well as failures.

RE: Clear Penetrating Epoxy

   Very many thanks for all your kind replies

I'm going to get some and give it a go, in due course .....

At present I'm still struggling cutting the scarfe joints ......

RE: Clear Penetrating Epoxy


I admire your energy and open mind. I would be remiss though, if I didn't caution you about stacking experiment upon experiment. Each experiment has an associated risk of failure. Each additional experiment adds to the risk that your project will fail.

One reason that boat builders tend to be fairly conservative, with materials and technique, is that a flaw in the construction of a boat my not become apparent until well after the boat has been put into service, or worse, not until subsequent boats with the same flaw have been built.

If a flaw in the construction of a boat cannot be repaired, much of the labor and materials that went into it will have been wasted. If a boat fails when in use the consequence can be serious to the people on board.

It's your money and your call, but experiments do not always succeed.



RE: Clear Penetrating Epoxy

   Hello Dick

Thank you for your kind words - Yep, I guess I'm the experimental kind of person

The idea of making my own puzzle joints was a moderate success & partial failure, hence why I am back to scarfes ..... though it was successful enough to be used on Panels 1 of my Sassafras 14 - the rest , boards 2 through 5 will all be scarfed

My intrigue of CPES has lead me to starting this thread and, all things being equal, it would seem a worthwhile trial.

I can appreciate what you are saying about stacking experiment on experiment but I am hoping to mitigate any risks with thorough thought  (famous last words !!)

My prime reasoning behind trying new approaches however is the advice from a good frined who said that I should "build my first boat, second" ..... this first build is a trial for me, to practice & explore techniques & alternatives, to learn, to find out

No doubt it would be easier to build from a kit, but I like the challenge of lofting my own cuts and finding out how things work, how they interfit and what improvements I can make for when I build "my first boat" after all this experimentation

The laser-cut jig I made for 4 inch finger joints has been an exciting & enjoyable diversion, though I realise now that scarfes are the way to go. I am glad I have learned this, or I'd be forever wondering about it .....

Such is the way my mind works

I have many more ideas to 'experiment' with, such as linear reinforcement beneath the gunwhale with carbon epoxy, using carbon/kevlar sheathing on the lower hull (below the waterline), fully sheathing the outer hull in 40 g/sm tissue, paint finishes versus varnish, using 25mm marine ply for both gunwhales instead of solid timber and a few others ....

But I do, most sincerely, thank you and everyone else who has replied to this thread and helping me to understand and learn from your own experiences

Sincerely, and with kindest regards,


RE: Clear Penetrating Epoxy


I'm a 70 year old Senior Software Architect. I've spent a career fighting the common wisdom that fears innovation, so I have some idea where you're coming from. But, as a former Army officer, I am also cognizant of risk management and the dangers of ignoring risks.

I sincerely hope that all goes well in your project and that on the occasions where things do not go as expected that you enjoy working through the problems as well. In my military career, I was taught that no plan survives contact with the enemy (or Murphy's Law). I also learned very early on that that was true and that you always had to have Plan B ready.

Best wishes,


RE: Clear Penetrating Epoxy

   Hello Dick,

Who's Mike ? :)

Oh, I'm not averse to innovation ........ I'm an engineer by trade. I'm also married !

My favourite thing to hear is "oh, that can't be done", or 'Its Impossible" ....

I have such fun trying to find out 'why' or finding another way around a problem.

My wife has horses and hurt her back a few years ago so we needed to get water 1/4 mile away and 150 feet higher than the river, but without any access to electrical power

Trial - and lots of error - resulted in a ram pump which continues to work to this day

I'm sure that there will be similar trials in boatbuilding but I'm looking forward to them all. I'd be bored as hell just assembling ready cut jigsaw of parts. Making mistakes is where one learns and adapts. To me, thats as much pleasure as enjoying the finished product

I've already had the first thing ' go not as expected' when I caught my finger jig template with the router cutter, instantly removing one of the acrylic guide fingers ..... hence why I'm back to scarfes

I now work in a non-engineering Safety Critical role which is very risk averse, for good reason, so its nice to get back to basic 'thinking' engineering

Enjoy your weekend


RE: Clear Penetrating Epoxy

  I got to try out the Total Boat penetrating epoxy sealer and I thought I'd pass along the results. It's basically a two part (2:1) epoxy similar to others on the market with a 100 cp value. It seems about the same thickness as US Composites 635 resin which I have sitting around ( 600 cp) so I'm not sure if either value or neither is real accurate.

It does spread easily on a surface but does not cover an area anywhere near that of the CPES product, nor does it penetrate to the extent that CPES does. I, however, did not dilute the product as I later saw in a vidio on JD's site. The demonstrator cut the mix with alcohol at about the same amount of hardener. This, no doubt would help with penetration into the wood surface. I also mixed some remaining resin with wood flour to see if it would behave as conventional epxoies do and it did so. Set up fine as a filleting compound. My conclusion is that it is basically a good general purpose epoxy with a competitive price and should work in most boatbuilding applications.

RE: Clear Penetrating Epoxy

The above are all great points, which is why I love this forum.  I too subscribe to the first boat second philosophy, which is why I made templates from my original lofted cut parts.

As a mechanical engineer, I also understand about not being able to solve if there are too many variables.  For example, I would be extremely hesitant to modify anything design-oriented, but having read every build blog I could find, I discovered that there are numerous ways to skin the assembly cat.  In the Eastport Pram manual, the verbage specifically says to add the transom stiffeners AFTER the boat is put together, but in the photos and half the blogs and more telling, in the Passagemaker manual, the stiffeners are added before the transoms are stitched together.  Those were the things that kept this plans builder up at nights.

With regards to later epoxy processes properly bonding to penetrating epoxy treated parts, this is no different that coating all the parts with a couple layers of epoxy while they're flat, then scuffing the mating surfaces for the filleting step.  The strength of the mated parts are at least as dependent on mechanical bonds and surface area as chemical bonds, which only come to play if you do the second step before the epoxy cures completely.

That's great info on Total Boat penetrating epoxy, especially about thinning it with alcohol!  Makes it go a lot farther too.  One thing to keep in mind is that it will obviously make the finished boat a little heavier based on the amount of product used.  This is a very fair trade-off IMHO if it makes the finished product more resistant to water damage.

These two threads are great and are really getting me jazzed about my Passagemaker project.  I just realized that in order to be done by Spring, without the crazy amount of pressure I put on myself to finish my EP before a family vacation, I need to get started now.

RE: Clear Penetrating Epoxy

 I know what you mean...Makes me want to bypass the model making stage and begin the real thing!

As a footnote, I went ahead and mixed up my old 2:1 epoxy and cut it with the denatured alcohol as they did on the JD site. I also had exactly the same situation. A pair of badly checked thwarts from a dingy I'm repairing. I sanded them down fairly aggressively but not enough to reach the bottom of the checks. The diluted epoxy mixture when applied with a brush almost immediately soaked into the grain and within a few hours was almost dry to the touch. The daggerboard case I had glued prior to painting the thwarts, with the same (undiluted) epoxy was still very wet and remained so for the next 6 hours.

  This morning the thwart has a fairly smooth finish with the same "oiled wood" feel to it as the CPES left. The resin darkens the wood considerably which may be a deal killer for some but I believe that will happen with any penetrating product used on old,porous wood. I'd post a pic but I can't figure this image hosting business out yet!

RE: Clear Penetrating Epoxy

   Okay, let's try this...

RE: Clear Penetrating Epoxy

I think the epoxy soaked version looks great!  See below.

One thing I want to mention is that the final volume of epoxy that has soaked into the wood is what counts, not the total volume of liquid applied when diluted with alcohol.  This could inadvertantly lead to less epoxy if you're not aware of this factor.  You can apply multiple coats while it's still wet.  Let the first coat soak in and apply second coat.  I did this on my picnic table top and I got at least three coats soaked in and one top coat before it started to kick.

RE: Clear Penetrating Epoxy

   Thanks for posting that pic CS; I'll get it figured out eventually! I actually did what you suggested when I coated it yesterday. I had resin left so I kept going over the board as the surface began to dull from absorbtion. I guess about three times. They are plywood thwarts BTW.

RE: Clear Penetrating Epoxy and Sanding

   When I was sanding the daggerboard for my NE Dory after putting on a coat of glass cloth soaked in epoxy, I was frustrated because by the time I got it smooth I'd cut through the cloth onto bare wood in several places. I'm wondering if applying several coats of Penetrating Epoxy might eliminate worries about doing this, since it won't be bare wood I've sanded down to, but rather wood soaked in Penetrating Epoxy.  Anybody have experience with this?

RE: Clear Penetrating Epoxy

  I'm not sure sure why you would even need to cover the board with cloth, unless to strenghten it or provide some protection. That being said, I personally wouldn't worry too much about protecting a daggerboard as you are always removing it from the case and can inspect it easily The inside of the case is the area, that in my opinion, should get the extra protection as it will likely never see a paint/ epoxy brush again...

RE: Clear Penetrating Epoxy

A couple of thoughts:

First, I would probably want to perfect sanding a fiberglassed part while being careful to not sand through.  This is important.  We often turn to the random orbital sander when in fact we should be hand sanding because power tools, although soothing to use, can be too aggressive in certain applications.  There's an inherent nobility in using hand tools when building wooden boats.

Second, if you're not going to somehow patch or recover the fiberglassed area/part, then soaking it with penetrating epoxy would have some benefit, but let's look at why you're glassing the daggerboard.  It's primarily to give it lateral stability/strength so it doesn't break off at the bottom of the daggerboard slot when it's keeping you from sailing sideways.  It's also to help fight all the wear and tear from dropping the daggerboard into the case and pulling it out a gazillion times over the life of the boat.  Penetrating epoxy won't help with wear and tear like fiberglass will.  With that being said, most of the daggerboard is underwater while underway, so penetrating epoxy will definitely help with intrusion, delamination, etc. especially where wear and tear breaches the glass/epoxy surface.  

Finally, fiberglass will also help with the fact that the leading edge/bottom of the daggerboard takes a lot of abuse during the beaching process if you're not quick enough.  Here in the PNW, we have rocky beaches that are very hard on daggerboards and rudders if you're not careful and nobody can be 100% crunch free.  I usually state "We're here!" when that happens...

As a side note, I used graphite epoxy as the top coat(s) for my daggerboard to help resist abrasion.  I didn't think about doing the inside of the daggerboard case until it was too late.

RE: Clear Penetrating Epoxy and NE Dory Daggerboard

   It's been several years since I built my NE Dory, and I didn't put fiberclass cloth on the daggerboard like I said in my post; chalk it up to an old man's diminished brain capacity.  I did, however sand through the coats of epoxy I put on the daggerboard, and from the description of how Penetrating Epoxy works, I think I'd've been better off putting a few coats of it into the daggerboard, then not worrying so much if I sanded through. A photo is at the bottom of the page linked to here:

RE: Clear Penetrating Epoxy

Hello All

Thank you so much for all your kind replies on this thread - it is invaluable for a first-time builder like me.

On the balance of things I'm probably going to get some. There is, as far as I can make out, only one supplier here in the UK - selling only 2 sizes (0.95 ltr & 1.9ltr) in either warm or cold

My boat is a lapstrake Sassafras 14 (yep, the discontinued one), so I'll be routing rebates into 4mm ply.  My plan is to use the CPES on the edges & joints (rebates) first, then assemble the boat loosely - then once it is square & true CPES the rest of the boat.

My plan is that every side/edge of every panel (even the bulkheads, gunwales & decks) are treated with CPES prior to epoxying.

WEST system is available here but I'm going to be using Petram Epoxy which has been used successfully by many boat builders here in the UK, both with fibreglass as well as more exotic materials

From all your replies, I know that CPES isn't very friendly, so I'll be using a full face respirator with VOC cartridges and disposable clothing (paper suits), and gloves, obviously.

As far as possible, application will be outdoors for the CPES using the Cold mix

Once treated, the boat will be sheathed in 6oz (163 gram) plain weave fabric externally on boards 1 & 2. I am still playing with the idea of sheathing boards 3 & 4 with 1.5oz (44 gram) fabric.

My chosen finish (until I change my mind again ....) is a cream painted exterior and varnished interior

For anyone who has built a Sassafras (or similar) I'd be very interested to know how much resin you used in your build - metric or imperial measurements, I'm 'fluent' in both

Thank you again for sharing your experience with me

Kind regards, Tony

RE: Clear Penetrating Epoxy

Update on an old thread:

I used West Marine's Penetrating Epoxy on various parts of my PMD boat hull.  I discovered much to my dismay that for some reason it doesn't "play well" with regular epoxy. 

After I stitched my hull together and filled the lap V's with thickened epoxy, I sanded all of the exposed corners with a roundover to reduce issues with impact on a sharp corners.  This exposed some of the core layers of the marine grade plywood and edge/end grain, so I soaked all of those seams with CPES.

Upon curing, it did a weird "beading" up on the previously epoxied planks.  Upon further application of additional layers of epoxy, the "beading" continued to show through, even after sanding previous layers.  It's as if there's some sort of wax or something that keeps subsequent layers from adhering properly.

With the only slightly comforting thought that "No good deed goes unpunished", I can categorically state based on empirical evidence that at least that brand of CPES is not a good idea to use in your boat building process.

RE: Clear Penetrating Epoxy

���Yeah, I'm not surprised . CPES has or had a high percentage of solvent. I tried it on deteriorated wood and was unimpressed.

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