34 years of using CPES

[billr]

CPES (Clear Penetrating Epoxy System) has been talked about by many on this forum, and they no doubt can add some good stories. I just realized that I have been actively using CPES on boats and buildings more than anything else to fix problems, for about 34 years. That’s a lot to say for an aerospace reliability engineer with 46 years of professional experience. When I first acquired some CPES in 1979, my view of what separated man from apes was our use of duct tape and wetsuit glue. CPES quickly got added to that list, because now I finally had a tool to kill the mold INSIDE the wood in my 1935 34’ yawl. CPES is a volumetric epoxy, designed to be infused into the wood, and be compatible with the mechanical properties of wood. There are many other applications it can be used for, and some which it can not be used for. So, I am writing up a series of project “stories” to illustrate those. As many on this forum are aware, the long service life requirements for military / aerospace hardware mandates a substantial amount of material science, process engineering, reliability testing with failure analysis, physics, chemistry, and many other professional disciplines. That is the life I live, so I will put that slant on these stories about CPES, and other “fix-it tools” that I like to use.
In 1979, the yawl had been on the hard for several years, had lots of deck leaks, and lots of rot. I was working on Kwajalein Atoll with plenty of heat, humidity, mold, and over 100 inches of rain per year. For six months I had tried all the typical chemicals from West Marine that supposedly work to control rot; none worked. Frankly, I was really depressed because it appeared that I had a boat that I could not fix. What I really needed was something that would soak the wood, kill the mold, and help restore the wood where possible. A yacht club buddy gave me a small ad he had torn out of a magazine, for a chemical company named Smith & Co in Richmond, California that seemed to offer such a product. Letters were exchanged, followed by an order, and pretty soon CPES arrived on Kwajalein, along with lots of instructions, plus other chemicals I ordered. It worked great. CPES has a very low viscosity and will run through the grain of wood faster than water will. My first project with it was to follow the instructions and infuse the resin at the top of a 6’ section of the boat’s stem. It didn’t have any soft rot spots in it, but the wood was definitely degraded. I drilled a staggered set of 1/4” holes near the top of that section to access the end grain. A masking tape “cup” was put around each hole. Then each cup was filled and refilled with CPES as it soaked into the grain. When the CPES showed up at the bottom after flowing through 6’ of wood, I stopped filling. That was a big chunk of wood, so I had to mix several batches of CPES to complete the job. In order to fill the holes that I had drilled, I had cut some 4” pieces of hardwood ¼” dowel. The idea was that after filling I would put a dowel in each fill hole, drive it home with a mallet (pretty tight fit), and then trim the dowel ends off after the epoxy set. I put the first dowel in, gave it one good whack with the mallet, and when I lifted the mallet off the end of the dowel there was CPES oozing out the end of the dowel. I was so amazed, that I went and got another engineer (yacht club guy) to watch me drive the next dowel. He was amazed, and immediately wanted to borrow some. (Note, these days I likely would have used something other than the wood dowels. Also note that if there had been a soft spot in the stem, then additional repair other than just the infusion would have been required. More to come on that.)
The Aerospace Connection - Over the years my aerospace engineering moved more into the world of materials properties and failure modes, accelerated environmental testing, and working with new technologies. As it did, my knowledge of the physics and chemistry of material properties grew, and that lead to new uses for CPES on my boat. Actually, having the CPES is kind of a power trip. It allows you to truly make permanent repairs. My Skookum 53 has a solid fiberglass hull, but there is a lot of wood in the decks, pilot house, and interior. CPES is the starting point for any repair or rebuild that I have to do on the boat if it involves any wood, as well as some repair cases for fiberglass too. I don’t need to have a custom wood shop fabricate new curved pieces of mahogany because the old ones on the companion way hatch have rot around the corroded screws that were used. I can mechanically remove the rot; use CPES to essentially make the remaining wood inert; fix the damaged area with epoxy / fiberglass filler bonded to the treated wood, and the new screws will never cause any rot problems, ever. Reliability engineers like that kind of stuff. So does my wife. She uses CPES a lot.
KEY CONCEPT - If you are using 2-part epoxy or urethane adhesives and coatings, the processes used to apply these chemicals is very important to the results. Understanding the sequence of reactions within the chemicals used provides insight into this. Low viscosity (very fluid) coatings use solvents to lower the viscosity of the mixed epoxy. Even with a low viscosity epoxy like CPES, it takes a while to infuse it through the grain of a large volume of wood. There are a number of wood material property issues associated with this which will be described in detail later. When the infusion places the CPES in the grain structure of the wood, the 2-parts of the epoxies will not completely react (ie. cure) until the solvents disperse. Where do the solvents disperse? Throughout the wood, and evaporation to outside of the wood. In any organic material (ie. not metal or solid glass), gases and vapor phase liquids will diffuse / permeate through those materials as a function of its concentration gradients in the material. So allow time for the solvents to disperse, so the CPES cures before going to the next step. More to follow.

[minaret]

Personally, I don't like Smiths. My biggest beef is that proper off gassing takes eight days. No one waits that long, most people think it feels dry to the touch on day two or three and go ahead and coat it. This inevitably leads to failure due to solvent popping. I prefer WEST with Tropical hardener heavily reduced with MEK. This penetrates just as well but can be chemical bonded to the next day with no sanding. I have also known far too many boaters who thought that CPES/Smiths was a cure-all and used it to "repair" structural members in a way that could get someone in trouble. Usually I end up fixing it properly in the boatyard, and it costs twice as much as it would have if it had just been properly dealt with in the first place. I much prefer to see suspect material removed and replaced as it should be, instead of throwing a band aid like Smiths at the problem.

[rognvald]

Originally Posted by minaret

Personally, I don't like Smiths. My biggest beef is that proper off gassing takes eight days. No one waits that long, most people think it feels dry to the touch on day two or three and go ahead and coat it. This inevitably leads to failure due to solvent popping. I prefer WEST with Tropical hardener heavily reduced with MEK. This penetrates just as well but can be chemical bonded to the next day with no sanding. I have also known far too many boaters who thought that CPES/Smiths was a cure-all and used it to "repair" structural members in a way that could get someone in trouble. Usually I end up fixing it properly in the boatyard, and it costs twice as much as it would have if it had just been properly dealt with in the first place. I much prefer to see suspect material removed and replaced as it should be, instead of throwing a band aid like Smiths at the problem.

Minaret, what do you mean by the term "solvent popping?" Thanks

[SkiprJohn]

Thanks for the report on CPES
kind regards,

[minaret]

Originally Posted by rognvald

Minaret, what do you mean by the term "solvent popping?" Thanks

That's when you have trapped solvents in the sealer or other coatings. The solvents end up eating the fairing compound, and often result in small blisters in the topcoat. This is called solvent popping. Common with certain sealers and hi build primers.

[billr]

Here is more on this topic:
Basics of Reliability Engineering, applicable to your boat - When the Navy buys a piece of hardware, the Request for Proposal will define the required service life, the performance parameters, and the environment that the hardware will be used in. Verifying that the hardware meets those requirements is achieved through a variety of qualification tests. If a test failure occurs with part of the hardware, the failed part will require the identification of the root cause of the failure (using the science of failure analysis) and that will lead to the determination of a Corrective Action. To just “Remove & Replace” the failed part without knowledge of the root cause will give you a high probability of failing the re-test for the same problem. There are some broad categories for failure modes. Mechanical failure modes generally involve cumulative fatigue from vibration and thermal cycling. There are many variations on this, but structural resonances, mechanical excitation (from engines or sea state), and thermal expansion often play a part in this. Electrical failure modes involve over-voltage, over-currents, electro-migration, and other effects. Chemical failure modes generally involve the degradation of the initial properties of a chemical or material (say a plastic, adhesive, metal, etc.) by things such as heat, oxygen, UV light, water, including corrosion, etc. Biological failure modes involve degradation of materials by living organisms like fungus / molds.
How does that tie in with your boat? The more you know about the failure modes that can affect different materials, the better prepared you are to avoid future problems if you have to do a repair or build something new. I use CPES a lot, but mostly for damage control. If I have a rot problem, the root cause is that water coming in from somewhere carried mold spores into the wood. If I remove the rot damaged wood and replace it with a great repair of scarfed in new wood, or an epoxy/fiberglass/filler mix, I have not yet done the corrective action to eliminate the root cause. Any of the initial remaining wood has been exposed to mold spores and is susceptible to a repeat of the same failure mode. But I can neutralize that by infusing the CPES into that wood. There are variations on this approach. If you have some rot which has not caused actual structural damage yet, infusing that area (and the surrounding area) with CPES can encapsulate and kill the spores associated with that rot. To the extent that there is still a lot of intact fibers in the wood, the CPES will strengthen that as well. That may be all that is needed if you are dealing with a small deck problem, as we all run into so many times around screw holes. Mushy decks, or mushy sterns on small Bayliners call for major surgery. But then again, I’m preaching to the choir for a lot of you folks.
Both the resins and the solvent system in CPES were designed to be compatible with the permeability, flexibility and breathability of wood. Depending how the wood is being used in the boat, that can be a design consideration for increasing the service life of the repair. Certainly, the qualification of the repair materials that provide a viable corrective action to alleviate the root cause of failure is a basic part of reliability engineering. More to follow.
Minaret had stated that CPES took 8 days for the solvent to get out. That was likely a different product. In the 34 years I have been using CPES in the tropics, in the desert, and in the Pacific Northwest, my experience has been typically 24 hours. If you are using a lot of CPES though a structure with a long infusion path, then 3 days is possible. Its pretty simple to tell when the solvent has vented: you can smell it if it has not. And the use of fans at the infusion site will accelerate the solvent evaporation rate.

[minaret]

Say man, I get my numbers straight from the side of the can. The graph with cure times in the link I will post is printed on the can. Note that full cure is listed as 8 days, for the warm weather formula. The instructions will also tell you not to overcoat with a primer before full cure. Why not just use WEST and chemical bond to it the next day, that way it's all one compatible system, sealer, resin, and fairing compound. It just works better.


I've used a whole lot of Smiths as sealer and hi build for varnish too. So did my wife in the many years she was a pro bright worker. Both our companies quit using it due to repeated failures from solvent popping and poor UV resistance.




Clear Penetrating Epoxy Sealer

[geoffh]

Thank you Bill for your opinion on CPES, as a tradesman and wooden boat owner, I have often had a lingering doubt as to whether I should have replaced or treated wood. I guess all repair work is still horses for courses, I'd still be inclined to replace the affected wood below the waterline. Cheers Geoff

[billr]

More on the reliability engineering issues for handling rot problems.
Design Trade-offs for a volumetric epoxy like CPES - If you are using a liquid epoxy it has material properties that will be different for at least “3“ states: the fluid that you mix up, the solid that you end up with, and the interim state (1 or more) that occurs during its application and use. For CPES, the mixed liquid state will have the amine and resin components starting to react as it is being carried by the solvent system into the wood. This mixture needs to be a low viscosity (i.e. thin fluid, like water) to penetrate through the wood, and the solvent system needs to interact with the natural resins in the wood to aid this process. The reaction rate has to be slow, because as the reaction occurs the viscosity will increase, and you do not want it to thicken when you have a long path through the wood to infuse. Once the infusion is done, and you are no longer pushing more CPES into the wood, keeping the reaction rate slow is still desirable, because now the liquid has entered a state where you want to you want to get rid of the solvent so that a complete cure can be obtained. The solvent will exit quicker through a mostly uncured epoxy than through a partially cured epoxy. So, there are some design trade-offs here to optimize the solvent evaporation, and there are certainly many variables (type of wood, etc.).
“8 days” Minaret had some good comments, one being the value of “8 days” on the side of a CPES can. However, that was the typical full cure time for the final solid state, but not an interim state attained during the curing process. Being of the reliability engineering mindset, I called Steve Smith (Smith & Co) to ask him about the cure cycle. I had contracted with his company a while back to do some research and development on a military project, so I knew I would get a complete answer. I asked “What % of cure strength needs to be attained after the solvents have left, so that you can apply another chemical? He noted a lot of variables, but that once the solvents were out (smell check), there was sufficient strength to do any follow-up bonding.
Process Control - Steve Smith also noted that copious amount of instructions that are packed between the 2 cans in each CPES kit they manufacture. This relates back to process control that I mentioned earlier. In the 1990’s, the Air Force required that prime contractors implement statistical process control for all their contacts. They are required to identify ways to measure the critical processes being performed during manufacturing, and monitor those processes to verify that they are maintaining them on a continual basis. The word “process” is kind of generic, but essentially defines a sequence of assembly. A “critical process” is one of the assembly variables that makes a significant difference in the outcome. If you have a product like CPES, and you are looking how well it infuses into wood, you can determine which variables make the most difference by testing many combinations of variables with a sophisticated technique called “Design of Experiments”. In Finland, there is a group called VTT, kind of like the Underwriters Lab in the US, which did just that on CPES. They published a report on it which can be found on the Smith&Co website (see the link on Minaret’s post of comments).

[billr]

Here is some reliability engineering issues at to why I like CPES (follows the my last post)
Back to Failure Modes - The value of CPES to me as a reliability engineer is that it has proven infusion capabilities and will control the mold spores (biological failure mode that is the root cause of the failure in the first place). It is also has the materials properties that are similar to wood (modulus /flexure) which means that I am not introducing any new vibrational failure modes. I spent over 6 years doing Highly Accelerated Life Testing (HALT), which includes using thermal cycling and vibration to accelerate mechanical fatigue to the point of failure. I broke over $20 million of military hardware using a massive test chamber which included what is called a ” 6 degrees-of –freedom” shaker table. When you break a piece of material it generally fractures at a point of high stress (called a stress riser). You can get that where you have a discontinuity in the material, one way of which is to have a point of change in the material. If you infuse wood with an epoxy which has a similar modulus such as that found in CPES, then there is little discontinuity. Depending on the physical location of the material, and the cumulative fatigue it experiences on the boat, this may or may not make a difference. However, that would take a lot of testing to determine, so it is much easier to just match up the repair materials as best you can with the existing material characteristics.
Time Considerations - But, when I am making repairs on my own boat I do not like to have to repair the same thing at a later date if I can avoid it. For all the reasons above I like CPES, but then again I use it on my personal time. It does take time to use it, time that many boat owners can afford and many boat yards can not. That’s just economic reality. More to come.

[billr]

Well, here is a typical classic use of CPES, for fixing something with a lot of mold, but not too much rot damage, yet.
Fixing the deck around the lazarette hatch - The deck on my Skookum 53 was built for being a workboat. Underneath the non-skid is fiberglass, over ¾” marine plywood, over fiberglass, over another layer of ¾”marine plywood. The lazarette hatch is an oval aluminum flush deck hatch. It rests on the lower lip of a cast frame that is screwed to the deck. Being recessed into the deck is nice, but it also collects a lot of water so that every time the hatch is opened, whatever is below the hatch gets a shower. In doing so the water runs over the inside edge of the lip, underneath it, and then down the exposed end grain of the deck plywood which was never sealed. Consequently, when I bought the boat the underside of the deck around the hatch was a mold garden, and the underside of the plywood had some exterior rot. The deck was still very firm, but corrective action was definitely called for.

We removed the mold and rotten wood underneath the deck around the hatch frame. The plywood was mostly in pretty good shape. On deck, around the perimeter of the frame, a set of 3/16” diameter holes were drilled, 4” from the frame, with a second set 7” from the frame, staggered from the first. The holes were drilled through the first layer of fiberglass, and down to the bottom of the first layer of plywood. These holes were then filled, and re-filled, and re-filled again with CPES until it was oozing out the end grain of the plywood that supported the hatch frame. Before we started the infusion, I had cleaned up the exposed end grain of the plywood with a Dremel tool and it looked pretty good. After we started the infusion, we eventually could see some little dark areas showing up where there was rot areas in the plywood. The Finland “design of experiments” study with CPES has some nice pictures of that effect, because the CPES will flow through rot areas in the wood quicker than non-rot areas. For this type of infusion, the CPES will strengthen the wood, but mostly what you want it to do is stop the progression of the rot intrusion. Of course if there is a lot of rot, or mushy wood, then you really have to remove that. But small areas, like the filaments of rot we had in the deck around the hatch, had yet to compromise the strength of the deck.

When the CPES started to ooze out of an area of wood around the hatch, we stopped filling the nearest hole, and concentrated on the others until all areas had oozed CPES. By the way, we used some masking tape to direct the oozing CPES into a can so that we could re-use it in holes that had not produced oozing yet. This takes a fair amount of work, and with about 50 holes it kept the two of us busy for several hours with mixing batches and using syringes to fill the holes. We were treating a substantial volume of wood in just that first layer.
The next day, we drilled the holes down through the next layer of fiberglass, and then most of the way through the second layer of ¾” plywood. That took a bit of measuring and then taping part way up the drill bit to make sure we did not drill through the bottom laminate of the plywood. We then repeated the filling cycle from the previous day. By the way, this multi-layer infusion approach is similar to what is used when preparing the bedrock base of an earthen dam, except that they use concrete under pressure to fill the porosity of the bedrock.

While the CPES outgassed the solvents for 3 days, we considered our options for filling the holes. There is a companion product to CPES called Fill-It, an epoxy filler which sets up with some of the characteristics of wood. You can put screws into it, and carve it with a wood chisel. We use it quite a bit, sometimes with added chopped fiberglass. However, this deck had seen 20 years of hard use while commercial fishing, so we decided to add something more structural. We ended up filling each hole with a dense mixture of chopped fiberglass and an epoxy laminating resin. So we were essentially adding 50 epoxy glass fasteners through all layers of the desk around that hatch. If you are cutting up your own fibers for use with epoxy, be sure to use fiberglass cloth or roving. The matt is pre-impregnated with polyester resin, and that causes some problems if you try to use it with an epoxy resins ….. different chemistries. Trying to pack anything into a 3/16” hole is time consuming. You have to get resin soaked glass in, without trapping air bubbles. We ended up using a mix of different diameter steel drifts, with two handed coordination. My wife got quite good at it.

We use a polybottle with a squirt cap for mixing the Part A and Part B of the CPES. Pour in equal parts (leaving at least a third of the bottle empty, shake hard for 2 minutes, and you are ready to go. We have separate little mushroom cans that we pour the Part A into from the 1 gallon can, and then use the cans to pour into the polybottle. Sometimes we will use a syringe to apply the CPES into small cracks. It is so fluid, it works very well in a syringe. Clean-up is with Lacquer Thinner. If you are using a syringe with a black rubber seal on the plunger, the Lacquer thinner will cause the rubber to swell, sometimes to the extent that it becomes useless. There is a new type of syringe with a plastic seal on the plunger that does not have that swelling problem. One occasional drawback on the older rubber seal syringes is that the tube part is given a thin layer of silicone by the manufacturer to allow the plunger to slide easier. Since syringes are used in aerospace a lot for application of adhesives, you can imagine the presence of silicone is not welcome. Of course it depends on the quantity used, but there have been adhesive failures on NASA spacecraft programs due to silicone contamination of small amounts of adhesive that was applied with syringes with rubber seals on the plunger. For the quantities we use on boats, it does not appear to be a problem. But if you are going to buy some syringes, look for the new kind with the white plastic seal on the plunger. You can clean those with solvents with no problems.

[billr]

Sorry for the small pitch type above. That is not what I pasted in. Perhaps the moderator can suggest a way to prevent that.
Billr