Interior Waterproofing

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Interior Waterproofing

Postby 18shamic » Mon Oct 09, 2017 12:37 pm

I know there are topics about this already, but none of them discuss the longevity/durability of CPES vs regular epoxy. Also Total Boat has come out with an "odorless" penetrating epoxy sealer; has anyone used it? I was planning on using the Total Boat, since it has no odor, and I will be applying it inside. Also, Is it okay to just use penetrating epoxy dealer? Or do I have to use traditional epoxy?


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Re: Interior Waterproofing

Postby PeterG » Mon Oct 09, 2017 2:42 pm

This will start a big discussion...
I have not used CPES but I plan to for encapsulating the interior of my boat. There are several options for waterproofing: using CPES, or neat epoxy (regular epoxy without additives) or a two-part epoxy bilge paint. There are oil based alkyd bilge paints too, but they are not as durable as epoxies. It's up to the builder what they prefer. My hull interior will be mostly covered, out of sight so I will keep it natural, no stain or paint, so I can inspect the condition of the wood. I picked CPES for this over epoxy as it supposedly will soak further into the wood grain. Epoxy will coat the grain but doesn't penetrate much at all. Flexing of the hull can cause cracking of that epoxy coating and allow moisture to enter the wood grain where rot can get started. Don Danenberg (antique boat restoration expert) has a great discussion on using CPES and modern bedding compounds like 3m 5200 to minimize the chance of rot on his boat restorations.
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Re: Interior Waterproofing

Postby TomB » Mon Oct 09, 2017 4:05 pm

Hey Micheal,

There is an article "Penetrating epoxy-legend or myth?" in the most recent issue of Epoxyworks ( )


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Re: Interior Waterproofing

Postby lakeracer69 » Mon Oct 09, 2017 4:49 pm

Add this to the discussion, I've been using Herculiner after doing a bit of research. It adheres right onto bare wood like nobodys business. It looks good ( hides a multitude of sins), provides an impermeable layer, and doesn't require any sanding. I think it wins just because of that. :mrgreen:
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Re: Interior Waterproofing

Postby PeterG » Mon Oct 09, 2017 6:00 pm

Very interesting article by a West System representative. I am usually skeptical of articles such as these, they are trying to sell you on their product being better than the next guy's. Though, everything the West rep states about the West epoxy and the Penetrating Epoxy A is consistent with Don Danenberg's reasoning and usage. Danenberg uses CPES as a semi-permeable sealer barrier, meaning moisture will pass through, but very slowly. Which is what Dananberg says he wants, in order not to trap moisture in the wood. He let's his top finishes such as paints and varnish provide the protection from water. That CPES barrier flexes with the hull without cracking or tearing the wood grain. But it is not the encapsulating waterproofing coating I had thought.
Looks like I will be rethinking this! CPES is a penetrating sealant that needs to be overcoated with something to provide a waterproofing protection. Most people here are using epoxy for that, many use marine paint, all have had reasonable success. Something to remember here is the hull construction of Glen L designs is very different from the old Chris Crafts, Garwoods, Century, etc. boats: they are subject to a lot more flexing than plywood or cold molded hulls, so epoxy encapsulation on those old hulls really doesn't make sense and experience shows it creates more problems than it solves.
There you go, I think I just talked myself out of CPES! Or, at least top coat it with something if I do use it.
Murphy's Law: Anything that can go wrong, will go wrong.
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Re: Interior Waterproofing

Postby BayouBengal » Tue Oct 10, 2017 8:51 am

I'll also warn you ahead of time that I'm a chemical idiot; so, the opinions I put out here may be worth even less than what you're paying for them.

Being the chemical idiot that I admittedly am, I set about finding out from the experts the best way to build my boat. I read Danenberg's two restoration books more than once, talked personally with Mr. Smith about his CPES product, talked with Paul Oman of EpoxyUSA, read everything Mr. Witt had written, read everything SystemThree put out, plus most everything that I could find on this forum regarding this topic. So, I was armed with the loads information. Actually, so much so that "analysis paralysis" set in, but I eventually decided on an approach that was skewed more towards Mr. Danenberg's methods than Mr. Witt's.

Reading the forum is great, but being able to talk live with some of the extremely knowledgeable guys on this forum is as we say in Louisiana, "mo better". In discussing my approach with Bill Edmundson over a cocktail at his beautiful condo in Alabama, he explained that restored boats like Mr. Danenberg discusses flex quite a bit more than new boats built in accordance with Mr. Witt's instructions. In other words, Mr. Danenberg and Mr. Witt are both right in their approaches, but since I was building a new boat, Mr. Witt's instructions are more applicable to what I was doing. Bill is usually right, but I was too far along by the time we talked, so I soldiered along with what I was doing.

My understanding is that the concern with 100% solids epoxy is that stress cracks may develop that allows moisture in, but then the cracks subsequently close partially or completely due to other mechanical forces. This leaves the moisture no escape route, thus, it sits in the wood and rots it.

With that in mind, this was my approach that I used for both the inside and outside of the hull. I used multiple coats of epoxy that I thinned myself with xylene and applied until the wood was saturated. I thinned it myself based on this info from Oman because 1)It sounded like he knew what he was talking about, and 2)I'm a cheap bastard who didn't want to pay the high price Mr. Smith demands for his product. Once the wood was saturated, I coated over with unthinned Silvertip epoxy. I specifically did not fiberglass cloth my boat based upon the what Mr. Danenberg terms the "ills of fiberglassing", meaning you have a thick inflexible layer of plastic (cured epoxy) very susceptible to cracking. So, if you're following me, I have wood saturated with epoxy that will probably resist any moisture absorption that comes its way coated on top of that with about four flexible layers of unthinned epoxy that shouldn't crack because it's fairly thin and flexible (according to SystemThree) and therefore should prevent any moisture from getting to the epoxy saturated wood in the first place.

A somewhat related note, I also put a 5200 bottom on my boat in accordance with Mr. Danenberg's instructions; so, my boat is built to flex.

So, what's the best way to do it? How should you do it? I really don't know but the info above explains my logic in the approach that I took. Time will tell.

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Re: Interior Waterproofing

Postby Mark-NJ » Tue Oct 10, 2017 6:04 pm

I spent a lot of time thinking about how to "waterproof" the inside of my hull, all the while knowing (believing?) that there's no such thing as "waterproof" at all. Water is insidious and will go where it wants to go. It's my job to not let it sit & pool...a dry bilge is a strong bilge.

I read everything I could find on penetrating epoxy, and came to the same conclusion as the link above: it's thinned with a ton of solvents, and solvents don't 'do' anything for the epoxy.

My boat will be in the water for 2-3 weeks at a time when we're in Maine, other than that it's day trips only. And I have a mooring cover, which keeps things mostly dry. So after much thought, I went with what I believe is the best solution for me: 2 coats of high quality oil-based primer paint, followed by 2 coats of exterior housepaint.

Not saying that's right for anyone's boat but mine, but so far it's proven to be as 'waterproof' as I need it to be......and for a ton less $$$ than using epoxy.

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Re: Interior Waterproofing

Postby JimmY » Wed Oct 11, 2017 9:41 am

More food for thought...

When I put my Squirt up on the lift two weeks ago, I left the drain plug in since I was planning on pulling it out the following weekend and there was no rain in the forecast for the week. Something came up, and I ended up leaving the boat in for an extra week, and we got rain, a lot of rain. I had forgotten about the drain plug being in, and when I showed up to load up the boat there was about 6" of water at the transom and the seat was almost under water. The boat had water in it for at least 4 days.

After draining it and getting it home, I checked out the interior. I used Sapele for the frames and battens, and apparently is gets much darker when it gets wet. I had a few spots in the rear compartment where the gas tank had scratched through the epoxy that were really dark. Also, the seat is held in with screws and I didn't drill these out enough and the screws cracked Frame 1 slightly around the screw holes, and these were very dark around them. Everywhere else the epoxy (System 3 Silver Tip) kept the water at bay. I double checked around both drain plugs, and both were dry with no discoloration, so I'm happy that I put the drains in properly.

I don't know how the epoxy will hold up over time, but at least I can do a visual inspection and see if it is starting to crack or leak. I'm not sure if opaque bilge paint adds any more protection, but after this experience I would recommend keeping the interior of your boat bright. The floor and sides in the cockpit are painted with System 3 WR-LPU gloss clear, and I'll keep a close eye in these areas to prevent sand and grit from wearing through the paint and epoxy.

I will repair the epoxy in the rear compartment, and drill out the screw holes, fill with epoxy and re-drill them. And, always remove the plug when the boat is on the lift or trailer.
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Re: Interior Waterproofing

Postby 18shamic » Mon Oct 16, 2017 5:11 pm

Wow - I never would have thought about un-thinned epoxy creating cracks allowing moisture to get in. I also never would have thought about bedliner. I have never heard of that one before - how has it held up?

I kind of suspected penetrating epoxy was just thinned epoxy sold at a higher price, so that wasn't surprised. I am probably going to do one coat of thinned epoxy with one coat of regular epoxy topped with bedliner in key places. I know bedliner is tough stuff - I will probably use it only on the very bottom of the boat, and in places that might get more abuse than other places; bottom of compartments, floors beneath carpets, etc.


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