barrier coat

[Troy Scott]

Folks,

I've been wondering why I've never heard of anybody using epoxy sheathing resin as a barrier coat. Wooden boat builders often use epoxy resin to seal the wood from the ingress of water or water vapor. They don't depend on one of the paint "barrier coats". They just use resin. So, why do we not use resin? It seems to me that, compared to something like Interlux Barrier Coat or one of the similar products, I could build a better moisture barrier by just building up maybe six coats of sheathing resin. The one I have in mind is made by System Three Resins. I think I could hot-coat the bottom paint onto it and avoid having to sand. Thoughts?

[Russell]

People do just use epoxy resin. West System is one of the more popular barrier coat methods out there, they offer a special addative/filler which also improves its ability to keep the wet stuff out.

[Troy Scott]

Russell,

Thanks! It's good to know that I won't be alone if I use fortified epoxy rather than paint as a barrier coat.

Bummer about your transmission coming loose! Several years ago I owned a Chrysler Sebring. I had to have the engine/transmission unit pulled for some repairs. Shortly after that the car began to handle oddly. It had the weirdest motion when passing over uneven pavement. I took it to an alignment shop, where they discovered that the Chrysler shop had left out the engine mount bolts! The whole under the hood group was held in place by gravity, hoses and wiring. SO..., I can sympathize.

[Troy Scott]

Russell,

Thanks! It's good to know that I won't be alone if I use fortified epoxy rather than paint as a barrier coat.

Bummer about your transmission coming loose! Several years ago I owned a Chrysler Sebring. I had to have the engine/transmission unit pulled for some repairs. Shortly after that the car began to handle oddly. It had the weirdest motion when passing over uneven pavement. I took it to an alignment shop, where they discovered that the Chrysler shop had left out the engine mount bolts! The whole under the hood group was held in place by gravity, hoses and wiring. SO..., I can sympathize.

[Russell]

Russell,

Thanks! It's good to know that I won't be alone if I use fortified epoxy rather than paint as a barrier coat.

For what its worth, my boat was done with west system about 7 years ago (before I bought it). It has held up great, but I did find one blister when I hauled out in Martinique this year. But it was a dime sized blister and on the rudder. Rudders are always more problematic and all things considered I think the barrier coat has done a tremendous job. The bottom was completely peeled first, absolutely no gel coat left below the waterline(which is initially disconcerting cause you can see the glass matt through the clear epoxy when you powerwash the bottom paint off, but nothing wrong with that). I imagine it was a huge job, but my surveyor when I bought the boat said it seemed very well done.

I imagine the tendancy towards paint style barrier coats is more about cost effectiveness then anything. I dont know much about paint barrier coats, my fuzzy memory is thinking interlux offers one that is a combo barrier coat and primer? Strait epoxy after a bottom peel then extended dry out time is probably still the best method out there, but also takes the most time and money. You are already in a position where you boat has been sitting out and drying for a long time, now is the time to do it.

I have a feeling that by the time you are done with your project that your CD36 will be the envy of the fleet. Why have we not seen pictures off progress?

[Troy Scott]

Russell,

I've just been too busy working on the boat to post photos. Plus, there's that learning curve thing... I've used the internet A LOT for help with my projects, but I've never posted photos. I will have to learn how to go about that. I'm sure I need to start one or two websites. My business needs one, and my personal projects do too.

[Mark Yashinsky]

Read West's literature on the process. A helper is handy and if you are going through teh effort, put on enough coats.

[Kurt]

Troy,
I used System Three on my last two boats with a great deal of success. I added pigment to the resin (alternating black and grey) as I applied it to keep track of the coats. I used around 3 gallons on my CD27. Never had another blister.
Kurt

[Troy Scott]

Kurt,

Thanks for the information! It's always good to find that someone else has successfully done whatever it is I'm considering.

Did you use the product System Three calls Sheathing Resin? Or did you use the thicker one they call bonding resin? Do you have photos?

I have learned that there is an additive which consists of some kind of microscopic "plates" that supposedly align themselves parallel to the hull in the sheathing layer. It is West part #422 barrier Coat Additive. I imagine it would help, and it sounds a lot like what Interlux claims for their barrier coat epoxy paint. I'm sure it would work as well in System Three epoxy as it does in West epoxy. HOWEVER, it's hard to argue with results like yours!

My boat lived most of her life "up north" and spent some time out of the water every year. When I finally get her in the water she will begin a new life as a southern boat, in the water almost all the time. This is a completely new situation where the DEMON BLISTERS are concerned.

Several folks have suggested that, since my boat has been out of the water for quite some time and is now completely dry, this is the perfect time to just go ahead and peel off the gelcoat below the bootstripe and replace it with epoxy. I'm sure that would be a permanent solution, but it seems so extreme! I'd rather just epoxy over the gelcoat. However, I would certainly be disgusted with myself if blisters develop later..... IS PEELING GELCOAT SUCH A BIG DEAL?

[John Vigor]

All this talk of barrier coating reminds me that the University of Rhode Island carried out experiments some years ago that showed that three coats of good marine enamel paint were just as effective as a full epoxy barrier coat.

Does anyone have details of that experiment? I know Don Casey mentions it in his maintenance books, but I've never seen the full results and conclusions.

It sounds to me like a very attractive alternative. A lot cheaper, and much simpler to apply.

John Vigor

[Troy Scott]

John,

I recall the same research. I remember thinking at the time that it just doesn't make much sense. It wouldn't be the first time that bad information got published. Good epoxy, in a reasonably thick coat, has been demonstrated (over and over) to be essentially water and water vapor impermeable. I've used a ton of it. I've never seen it blister. On the other hand, I've seen marine enamel bubble up and blister just because someone left a wet cockpit cushion sitting on it for a few days. I'm very skeptical of this supposed property of marine enamel. I doubt marine enamel would prevent the kind of reactive blisters we're concerned about on the bottoms of our polyester boats. I wonder if there was some unknown mechanism at work that affected the results of those tests.

[Kurt]

Troy,
I did my System Three barrier coats in 1994 (CD26) and 2004 (CD27). On the 26 I did a complete removal of the gelcoat because the blistering was extensive with thousands of tiny blisters leaking blue ooze between the gelcoat and first layer of mat. On the 27 I did not remove the gelcoat but did thoroughly sand the gelcoat. I used a 7" high speed disc sander on the 26 and a 6" random orbital on the 27. The epoxy I used from System Three was their plain vanilla laminating resin. No additives other than pigment was used. I used the pigment to keep track of the coats.
As you know, straight epoxy is a little more difficult to use than other products such as Interprotect 2000 which is formulated to be a little more user friendly and forgiving. But pure epoxy resin is just about the most waterproof coating you can put on a hull. Allegedly, vinyl ester resin is superior to epoxy...but it's even trickier to use.
Kurt

[Kurt]

Years ago I too read about the University of Rhode Island study regarding barrier coatings and the moisture exclusion effectiveness (MEE) of various products/coatings. And yes, alkyd enamel was proven to have a high degree of MEE but that study was done over a short period of time. I doubt the enamel would hold up on a hull for years and years whereas epoxy can.

[Troy Scott]

Kurt,

I had not heard that VE is a better barrier. I'm very familiar with VE. Is there a particular article or study you can reference?

[Kurt]

Troy,
There's a wealth of information on the internet regarding osmotic blistering. When I researched the topic back in the early 90's, I remember reading that vinylester was the most water impereable resin being slightly better than epoxy and much better than polyester. But vinylester is also the trickiest to use and doesn't have the superior secondary bonding characteristics of epoxy. I would suggest you google vinylester barrier coat and epoxy barrier coat and read up on it. Then draw your own conclusions.
Kurt