Epoxy Coating GRP Hull and Bilges

Hello, and thank you in advance.

I am researching about Epoxy Coating my 30 years old solid fiberglass hull. I am trying to find the best epoxy barrier coat for the hull, it seems most have fillers, but I know a filler may augment the permeability of an epoxy coating, and I have heard/read about the different properties of epoxy resins and ease of application.

My plan is to sandblast the hull, clean and apply a deliberate coat of CPES, if a lot gets absorbed, wait 2 days and apply another one, than coat with an epoxy barrier coat.

Any suggestions as to what is the best resin or barrier coat to use?

The other question is regarding the bilge: I would like to paint it, now, what kind of paint?

The best bilge paint I have ever used is epoxy resin with titanium dioxide as a pigment. easy to apply, less toxic than the solvent based stuff, great adhesion, longer lasting and very easy to clean.

But I am wondering about osmosis, if the water particle penetrating through the hull doesn't have an easy way out, may lodge itself in the laminate and begin the osmosis acid…

Or is it just the opposite, the bilge being sealed, moisture will not go through as much and less risk of osmosis to begin from the interior?

Thank you once again.

Carlo

 

Does the hull have osmosis damage now?

 

Nothing showed up in the survey.

 

Welcome to the forum.

You have some misconceptions about the procedures and epoxy techniques used.

First off, if you don't have blisters or evidence of osmosis, it's very probable your hull was built with a better grade of resin, which prevents these problems. Simply put, you might not need a barrier coat. Models that were prone to these issues are fairly well known. What is the year (1984?), make and model?

CPES (it's not water proof, not even close BTW) is a complete waste of time and money on a polyester hull, so toss this notion altogether.

As to a "barrier coat" in the bilge, well it sounds like you just need a good paint job, not an actual barrier coat. The best paint would be a two pack, two stage polyurethane, though this may be a bit over the top for a bilge, so possibly just a single stage polyurethane, should be considered.

You should address an osmosis prone yacht, but there's really no need to go crazy about, particularly if there's no signs after 30 years of service. Don't get me wrong, you're correct to worry, as moisture vapor can penetrate these boats (the ones with screwed up resin layups) and the freeze/thaw cycles along can do lots of damage. As I mentioned, if there's no evidence of it after 3 decades, you're probably safe.

As to resin systems, well there's a couple of approaches - the cheaper one is an epoxy paint system, which isn't bad, but not the best either. The other approach is a true epoxy coating of sufficient thickness to prevent moisture vapor from penetrating the hull shell. Considering you haven't any signs currently, you can add some "insurance" with an epoxy paint job, over a properly prepped surface (the real key to any paint job). In the future, you may very well need to take more drastic measures, but why cut off your leg, before gangrene sets in . . .

 

Thanks for the reply, she is 1983, 38 ft one off, Chuck Paine design, built by Roger Morse.

First, the salt water side, it is a preventive measure, as I plan to live on this boat for as long as my life and my wife's allows, so I would like to think 50 years, being that longevity is in the family. We all know that water will eventually damage a polyester laminate, it may take 300 years, or another 30, I don't want to be around to see it. The CPES is mainly to aid adhesion, since I have lots of it left over, and also if there is anything in the beginning stages in the outer layer that I can not see, it should encapsulate it and help a little, plus it will help to diminish water penetration a little and to fill up the dried out polyurethane outer layer, giving it somewhat of a new life.

As you mentioned above "you are probably safe", probably is not surely, if I am not sure, I will prevent so that gangrene never sets in.

As far as the bilge, why do you say I need a barrier coat? is it not better to let the hull breathe so the water molecule that entered it from the other side escapes? That is my real question, not which kind of paint.

2K poly is really bad paint for bilges IMHO, it has poor adhesion, it gets stained easily, and chips easily too, I would need lots more prep work, priming and it is very toxic, I don't feel like going into a lazarette with a can of that stuff, neither feel like sanding and painting it again in 10 years when I am older, one part poly does not exist in my book, epoxy resin and Ti02 I just clean it and forget it, and it is so easy and fast to apply, my doubt, once again is the osmosis process..

Thanks once again for taking your time, sorry if I was not clear enough.

Carlo

 

Don't make the mistake of over thinking this. Take PAR's advice. I'm finishing up a restoration on a 1973 Silverton (she's going in in July guys!). This boat had it's issues for sure but hull blistering wasn't one of them. It sat in the water for decades before I took it on and I found absolutely no blisters. I repainted the engine bay as I installed new beefier stringers. Painted with Interlux Bilgecoat mainly just to pretty it all up. The rest of the bilge is unpainted and I'm fine with it. If the layup is good quality and yours sounds like it is I wouldn't worry too much if at all.

Good Luck,

MIA

 

Thanks, MIA, but my issue is, I don't want to use polyurethanes or enamels to paint this, if I do I will be repainting it in 5 or 10 years max (I know of experience + I am a varnish/paint/color maker), plus I need to prime, so what I am left with? Epoxy paint, well resin and Ti02 is so much better, than I am left with the osmosis question, the only reason I would use any of the weaker paints would be if the water molecule needs to exit through the bilge.

I have lived aboard for more than 8 years and minimizing maintenance is #1 priority now.

Anyone knows the answer to my osmosis question?

Thanks again.

 

CPES isn't going to improve adhesion, its' just diluted epoxy (very diluted in fact) and it's quite porous as well. When cured it's elongation is poor, tension, compression, modulus, etc. are are very low compared to a standard 100% solids marine epoxy. There's really no use for it on a polyester hull.

Chuck would have spec'd a quality resin and Roger would have insisted on it, knowing the alternatives. Also, since it was a custom one off, there wouldn't have been the pressure to build to as fine a price point, so the tabbing and laminate schedule would have received the attention they deserve.

If you want to barrier coat, just to be sure, there's several off the shelf products that will do fine. Paint choices abound, though they will not stop moisture vapor ingress, only a minimum of a 10 mil 100% solids epoxy coating can do this, on pretty much any substrate. Call Paul at Progress Epoxy coatings (Epoxy Products.com) and ask about his Alumathane paint. I've tested this stuff and it's tough. Tell him PAR sent you.

 

Thanks PAR, I spoke with Paul, he was really nice, he recommended me his Waterguard 300 for the bilges, and perhaps may be the solution I am looking for glueing Thread Master (their epoxy glue cracks, and sikaflex is not tough enough and the edges chip)
http://www.epoxyusa.com/product_p/ep05.htm

I also would like to thank you for the Aluthene tip, will not use it for the bilge but it seems like the solution I was looking for my cast aluminum portholes, since no one local anodizes it, also as an engine primer.
http://www.epoxyproducts.com/aluthane.html

As far as the CPES goes, I need to call Steve Smith's company and speak with them some more, his product is not just epoxy with solvent, I have used epoxy with solvent before, experimented and done lots of tests, it is completely different than Smith's CPES, now there are other companies making epoxy+solvent and calling it CPES, very different stuff. First of all it is made from tree resin, not petroleum, more expensive to make and has different properties, and as a varnishmaker I know that by changing resins much changes.

This is an interesting text on CPES and osmosis.

http://www.smithandcompany.org/GRP/GRP.html

Thanks again

 

I was just in the bilge of my 1971 cuddy. The most durable thing in there? Gel coat.

I wouldn't paint with a 2 part polyurethane either, for the same reasons. I had some get through a mask once (I didn't have a fresh air suit) and I almost needed an ambulance ride that night.

I haven't used it below waterline, but a layer of vinylester(epoxy) is not uncommon to prevent osmosis. I use vinylester laminating resin for mechanical bits due to the good properties but no epoxy aliphatic amine hardener. (People call it half polyester and half epoxy, but I think that's a bit of a simplification) And you can thin it out and tune gel time simply with styrene monomer addition and hardener proportion. Unlike traditional DGEBA epoxy.

I might give the folks at Duratec a call. There are likely others. I used their vinylester surfacing primer to get gel coat to stick to some traditional (west system) epoxy laminate. They might recommend a product for sealing the hull.

For a glass boat, my biggest problem has been the non-glass parts. I have been replacing bulkheads in my 1971 with divinycel H80 cored and vinylester/ glass skinned panels.

Good luck.

 

We often use interprotect 2000 in the bilge, nothing majic about it, its just a decent white epoxy primer that we always have in stock to freshen things up, usually only need one coat so no problem trapping vapors. We will sometimes use gray under the engine . I agree with par on the cpes, i have actually tried the stuff years ago on wood, pretty much a useless product. If you have never had osmosis you can just use 5 or 6 coats of a paint system such as interprotect 2000, if you have had osmosis you need to barrier coat first, after repairs, with 100% solids epoxy before the paint system.

Steve.

 

The law suits and testing data on CPES have long been settled and there's no real debate, to it's effectiveness as a coating/sealer, it's physical properties, it's ability to water proof, etc. I'm sure the Smith Brothers, will offer up the usual marketing hype, such as their "organic" resin base, of course they'll conveniently forget to mention, the several other compounds that are also in the solution, are petroleum based. not to mention the directly conflicting compounds (both hydrophobic and hygroscopic in the solution). I have to admit I have considerably more understanding of the chemistry at work here, but the data is available with some leg work.

This is part of a post I made a few years ago, addressing penetrating epoxies in general, including CPES:

1 - Penetrating epoxies (CPES, etc.) do penetrate wood (so does lots of stuff).
2 - Penetrating epoxies do leave behind a coating, within the cellular structure of the wood.
3 - Penetrating epoxies do limit the amount of moisture vapor mitigation into surrounding substrates.
4 - Penetrating epoxies can be used to control moisture content in wood.
5 - Penetrating epoxies are not a very effective "sealant".
6 - Penetrating epoxies are an effective wood primer, under paint.
7 - Dan Dannenberg and the like minded.

Okay, now Richard and others are bunching up their panties. Maybe partly because they haven't seen my logo in a while and partly from the statements in the second paragraph. The second paragraph is completely true, tests have plainly born this out, the debate has been over for some time, but . . .

1 - Testing has shown that one; the addition of solvents does help epoxy resin penetrate wood and two; that this particular trait isn't necessary, nor desirable for a good waterproof seal. In fact, testing has shown that the amount of penetration into wood doesn't have anything to do with the ability of a product to make something waterproof. What has been found from testing is, it's all about the quality of the coating employed, not how far it's penetrated into wood.

2 - When a penetrating epoxy is applied, it eventually leaves a coating of plastic within the wood structure. Because of the reactive diluents and modifiers used in most penetrating epoxy formulations (their big failing point BTW) are grotesquely unable to offer moisture vapor ingress protection, though they can slow it a little, depending on application technique.

3 - Since we've gotten to it, these epoxy types can be employed with other products to effectively prevent moisture vapor penetration (the real goal of waterproofing). Interestingly enough the usual "other" products are epoxies with much higher, preferably 100% solids content after cure. The amount of moisture vapor ingress a penetrating epoxy can resist, is purely subject to the amount of solids in the final results of one's effort. In other words, one coat of CPES really doesn't do much, but several can be considerably better.

4 - There are occasions where penetrating epoxies can be employed with good success. This once, not so long ago was on just about everything imaginable, but in recent years has diminished considerably. Some times the "hot on hot" method can't be employed, so a vehicle penetration might be considered (though a non-reactive modifier is a much better choice). This is when a penetrating epoxy should be considered. Other instances may include partial restoration of highly damaged material for molding, sampling or as a fore runner to restoration. I've used penetrating epoxies to hold damage at a constant, until I could get at the cause or address this element of the project. Admittedly, I find I have less and less need for this material (penetrating epoxies), but occasionally, it's just the ticket.

5 - As has been suggested and the physical properties clearly show, penetrating epoxies aren't an effective sealant, if waterproofing and moisture vapor penetration into a substrate is a desired goal. Most of these products dry full of out gassing pin holes and literally flash off their bulk, leaving a web of, non-inter linked, overlapping carbon molecules chains with limited ability to prevent moisture getting past it. Even with several coats, the best thing you can do to a penetrating epoxy is apply a full strength, 100% solids epoxy over it, which makes one wonder why employ the penetrating epoxy in the first place.

6 - Because of these types of products penetration, they make good paint or varnish primers. Personally, I'd rather use viscosity reduction techniques on regular epoxy resins, if I was going the epoxy as a primer route, but penetrating epoxies are also very good. I see no advantage to their use, except on highly flexible substrates, where they'll out perform a regular epoxy all day long. Given the price of primer in comparison, I use primer unless I have a specific reason for penetrating epoxy.

7 - Those that know me, know I don't care much for folks that are married to their ideals so fervidly that new information just can't be absorbed. I consider these types useless and tend to question all they might have an opinion about. Larry Pardey is a classic example of this insidious mentality. He still thinks epoxy is a fad. Dan Dannenberg is a skilled and able craftsmen, but also one of these stuck in his own rut types. He can't see past his own nose and this is a sin as he's got some mad boat building skills.

I've spent my whole life making adjustments to my understanding of the world. I was taught Pluto was a planet, but apparently it's only a planetoid. I'll bet both Larry and Dan just can't get their head around this and insist it's just a passing fad.

You can debate the penetrating epoxy myths all day, but the tests and the jury has long since come in. The big selling point with penetrating epoxy is it's ability to penetrate. Tests has shown it doesn't matter what the penetration level is, it's the quality of the cured coating that is the determining factor. This means that the penetration thing is nothing more then a marketing ploy. Just like using the word copper in a bottom coating product or the word epoxy in a paint product. Both words are designed to sell product, regardless of testing results.

 

Thanks for the posts.

I think you are missing the point, sorry. CPES on wood is similar to how I seal wood with varnish. Wood in the microscopic level looks like a multitude of straws, the way I like to seal it (for interior varnish) is by fist applying a strong solvent, let it evaporate completely, with it some of the oils in the wood will evaporate, leaving an empty space for what comes next. (old technique used in floor coating to aid penetration)

Apply a coat of the solvent of the varnish to be applied, to aid penetration, next apply a extremely dilute coat of varnish that will only coat the border of the straws and not fill them up, it can be a 20:1 solvent to varnish ratio, or 30:1. Soak the wood, let it have as much as it takes, let it dry, than continue. Will this first application completely seal the wood?

No it won't, but it will penetrate deeper in the structure of the wood and the right resin or varnish will become "part" of the wood, it will change the way wood reacts with moisture, you can not get the stuff out unless you remove that portion of wood. A similar process can be traced back to Italy in the 1600's, also the german chemist Friedrich Hoffmann wrote about it in the early 1700's and how it helps in the protection of wood and paintings. You should experiment with it and see for yourself.

Now you can take a West Systems resin and impregnate as much as you want, you will not get as deep as penetration and incorporation into the wood as the way I do it. I take CPES and saturate the wood, push it into the wood, give it as much as it takes. Another great thing to do if the piece is not too large place CPES on a tray and place the end grain into it, the capillary action will do the work, it is amazing how far it goes.

Once dry enough that you do not smell solvent anymore, I apply a very thick coat of Illstreet Composites Infusion Resin, let it get absorbed (20 minutes?), come back with the tip of a folded cloth and remove all excess, once dry to the touch another coat of West Systems resin wich I like to apply using the pad printing method if it is a small or medium area. You get far superior penetration into the wood with a thinner and much stronger film and the stuff becomes part of the wood, no just laying on top of it.

I am still not happy with the West Systems one, sems like the weak point in my chain of events, I need to try Steve Smith's laminating resin, it may be just the one I am looking for, less brittle than the other stuff, and more flexible, the old fat over lean rule.

Resins, Solvents, Fillers, Pigments, Dyes, Oils, Acids, Alkalies are all tools, many ways to to use them, for each job or purpose a different tool, don't blame the tool for a job that did not go right.

Thanks again.

 

Nothing personal, but after many tests (mine and others), I know precisely how effective varnish (traditional and modified), shellac, polyester (single and 2K) and the other usual "wood sealers" are and how they work, right done to the sub molecular level.

I beg to differ (again the testing thing) but a properly executed hot on hot application of a 100% solids epoxy (West System included) will penetrate as deeply as anything else, but the penetration depth isn't the point, if the coating will permit the moisture vapor molecule to permeate through it.

The bottom line is permeability of the moisture vapor molecule, not depth of penetration into the substrate.

Varnish is only a little better then traditional oil finishes (Dutch oils, etc.) in this regard and this is simply because of the driers and solids content in comparison. Shellac is about 10 - 15% better then traditional varnishes at resisting penetration of the moisture vapor molecule, with the polyurethane varnishes and single pack coating getting a little better than this. The two pack polyurethanes are significantly better, but still pale in comparison to 100% solids epoxy.

The real story is "does the wood move" after you've made the application, which is an indication of how effective a "sealer" actually is. None of the treatments you've described stabilizes the wood and it will expand and contract with environmental changes. This will test the pull out strength of the fasteners, the glue lines, etc. with every cycle. Only 100% epoxy can say this (one of the reasons the Smith Brothers had to change the name of their product and their advertising BTW). You don't even have to soak to wood, as the coating can be purely topical prophylactic in nature. Once an appropriate film thickness is applied, you're done, no penetration, no dilution and many coats, just apply and call it a day. The wood doesn't expand and contract with moisture content changes, but stabilize about where the content was at application. This is true wood sealing and water proofing.

I'm not going to comment on the test data of some 300 year old German, who was probably just pissed he couldn't turn corn meal into gold.

If you're so convinced, try this simple test. Take a hunk of balsa (several for a base line and other products too, preferably all from the same stick) and use whatever treatment you'd like on each, completely entombing the piece(s). Do it to formulator recommendations and instructions (a 10 mil coating for epoxy, for example) and then place the fully coated hunks of balsa, in a fish tank of water, for a month, after weighing each before submerging them. After a month, pull them out (dry them carefully with a towel) and see how much more each weighs. Your not going to like what happens to the traditional oils, varnish, shellac, polyurethanes and penetrating epoxy samples, as they'll all weigh significantly more (I can tell you pretty much how much too). The 100% solids epoxy will resist 97% of moisture vapor ingress, which is hands and feet above any of the other concoctions and methods and though not completely "water proof" (compared to a glass jar for example) so close that it doesn't mater and the wood becomes moisture stable, which none (yep none) of the other products and/or techniques can prove or claim (as CPES used to).

 

Par, thank you for your posts, and for taking the time to write it, I believe we are both talking about different points, and I am sorry if I did not explain myself and I believe you misunderstood my varnish comment. My posting was about Osmosis, I got the answers I wanted by talking to a few different chemists. and an experienced surveyor Either way, thanks again.

As far as penetration, you are wrong, and a coating is not just a simple black and white all purpose produce. Epoxy is also permeable, if you want less permeable try paraffin, but it has limited use. Depth has importance in several types of failures, and since these materials are permeable and can get hit, scratched cracked, if there is a small failure and the coating in on top of the wood not in the wood, water may ingress and bacteria will follow. And I can clearly see that my 3 layer system stabilizes the wood better than the thick epoxy only.

You speak about varnish as if they where all the same, a 4:1 Congo Copal linseed varnish, or a 1:1 East india linseed, or a pure Amber low heat solved with no oil, or a Strasburg Turpentine linseed, or a Rosin Tung, are completely different animals, and the same materials can produce completely different varnishes depending on how you cook or prepare the materials, or whey they come from, if you dilute it while cooking or afterwards, or what you dilute it with.(even something simple as shellac can have a billion different characteristics depending on where it comes from and how it was treated afterwards, and if done right has much better adhesion than epoxy)

Not to mention that all of the cheap modern varnishes made of low quality synthesized materials available in cans which will fail in the worst possible manner and will look really bad in less than 30 years, (not good business practice to sell varnish that cost less than the materials to make it) which is the reason I got into making varnish in the first place (for my own use), either you buy a cheap looking affordable varnish, which will fail by becoming ugly, or you spend $70 for 2 oz of good stuff that will last 300 years if well cared (just look at the intact varnishes from Robert Martin made in the 1700's). And none of the modern varnishes can outlast the carriage varnishes of the old days, and look cheap in comparison (well they are cheap). You mixed up my varnish comment with the permeability of an unremarkable varnish, and did not think about the difference of one varnish and a varnish system consisting of dissimilar layers.

Take a piece of dried epoxy and take a piece of fossil amber and place them both in the fish tank, wait 600 years, than you tell me. As far as the comment that every chemist in the past has been in search of gold, sorry, that is a myth far from the truth. Speaking of know-how in material manufacturing, product availability, cost to quality comparison, just take a painting by Raffaello Sanzio and any by any modern painter and tell me which colors and films looks cheap... not an accident of a romantic search for gold making in a novel. Sorry, we evolved in making stuff cheaper and in large quantities, not necessarily better.

As far as my conclusions on the subject the thread is about. Te best solution I have encountered is to first apply CPES, as no other epoxy product will penetrate as deep into to a polyester hull as it does, yesterday's tests made that clear, is soaks in nicely, so it will aid adhesion and encapsulate anything bad in formation near the outer layer, than a coat of Water Guard 300, to be followed by anti fouling, inside the bilge the same except for the anti fouling. And thanks again for the Alumtech tip, bought it already.

All the best and thanks again.