Lets Talk Epoxy

[Dennis Crews]

More than once on this site I have read reminders from experienced boat builders that we should remember that epoxy is not waterproof. Why then do we go through all the work and expense to coat our entire boats with it? What is the main benefit if not waterproofing the wood?

[Dave M]

Dennis, it is a good sealant that soaks into the plywood and seals the pours. It also adds some degree of strength. It fills up all the pin holes created at areas where filler was used to bridge a gap, etc. It also gives the natural wood a nice tone. In essence it is a primer coat, only clear. Treat it as such. Paint it or clear coat it from there.

[Will.Smoot]

Technically speaking from a general boating industry stand point, (when done adequately) encapsulating wood with epoxy provides water proofing, weatherability and strength as well as variable mechanical properties (when a reinforcement fabric is used). The main reason for completely coating a boat or any outdoor project with an epoxy is to prevent moisture cycling, which causes wood to expand and contract continually. This cycle causes fatigue over time to epoxy adhered joints and coatings and causes delamination or an abrupt failure. Complete encapsulation prevents this phenomenon. Painting or applying a suitable varnish over epoxy is also critical to prevent UV degredation, which is epoxy's kryptonite. Just some food for thought.

[ZUL8TR]

As Will correctly stated with epoxy you get additional strength but I like the quick build clear 2 coats of epoxy provides so only 2 -3 coats of varnish are needed to get a real deep look of the grain, never did like the work involved with 8 or so coats of varnish to build.

[guedo499]

It took Will 5 years at WSU to figure all that out.

If you went to WWU Will, you would have learned that day one.

All it good fun! Wish I won your basket goodies of System 3 at the banquet - maybe next time.

[Will.Smoot]

Jon, LOL! Almost went to WWU. But WSU was too enticing! You know our Headquarters is only a stones throw away from you! Come by sometime and I'll show you around.

[Dennis Crews]

Wow..ask and ye shall receive. Thanks for sharing all the knowledge.

[Raymond]

Yes, this is all great discussion; thanks for sharing!

I have also read elsewhere on Hydroracer that epoxy is not waterproof. I am as far from being a Chemist as one can be but I thought I understood the properties of epoxy at it applies to barrier coats. Can we explore this notion that ‘epoxy is not waterproof’ a bit further? Maybe there are different understandings of the definition of the word ‘waterproof’? Here is the first thing that came up when I googled it. In what way do we mean it does not meet that criterion?

[ZUL8TR]

Interesting: water resistant not equal to impermeable or impervious, the latter two are conclusive while resistant is not but depends on conditions.

water resistant

able to resist the penetration of water to some degree but not entirely.

impervious

not allowing fluid to pass through.

synonyms: impermeable, impenetrable, impregnable, waterproof, watertight, water-resistant, repellent; More
.
impermeable

not allowing fluid to pass through.

synonyms: watertight, waterproof, damp-proof, airtight, (hermetically) sealed, vacuum-packed, zip-locked

Epoxies are tested under ASTM procedures for a degree of water resistance by weight gain of a sample of epoxy over time as one possible test for water resistance. See item 6 in following:

http://widget.miracote.com/download/...20Dec%2005.pdf

Here is one water resistance test of epoxies, none that I am familiar with. Solvent based are not very water resistant while high solids epoxies are very water resistant. Boat construction use the high solids epoxies but some of those have Benzyl Alcohol solvent in them some have no solvents.

http://www.boatcraftnsw.com.au/botec...20Analysis.pdf

First I am not picking on West or Raka they just provide easy to find MSDS. Here is West epoxy resin MSDS and note the Benzyl Alcohol content at 10 to 30% so water resistance would presumably be less than a 100% solids epoxy since the alcohol will reduce the coating mil thickness when set compared to 100% solids epoxy. But more coats would provide additional water resistance. I could not locate any West system water resistance tests. Interesting West claims no volitile solvents in their epoxy but Benzyl Alcohol is a volatile solvent?

http://www.westsystem.com/ss/assets/MSDS/MSDS105.pdf

Do not know if the West hardener has any solvents in them since the chemicals they list in the MSDS in the slow and fast hardener are names that need research to determine what they are. Here is the slow hardener MSDS

http://www.westsystem.com/ss/assets/MSDS/MSDS206.pdf

Raka epoxy also has Benzyl alcohol

http://www.raka.com/raka%20127%20900...superfast.html

There is more to find out about epoxy as there are many different brews out there.

Here is a read for epoxy chemistry (need some chemistry background)

http://www.epoxyproducts.com/chemistry.html

[Smitty]

What's the source for the definition, synonyms, et al? Because the industry does NOT hold the terms "waterproof" and "water-resistant" to be synonymous. For instance, Weldwood Plastic Resin Glue (the powder and water stuff) is described as "water resistant," so joints glued with it should not be immersed in water for extended periods (not wet-moored in a marina), whereas Weldwood Resorcinol Glue is "waterproof."

[ZUL8TR]

What's the source for the definition, synonyms, et al? Because the industry does NOT hold the terms "waterproof" and "water-resistant" to be synonymous. For instance, Weldwood Plastic Resin Glue (the powder and water stuff) is described as "water resistant," so joints glued with it should not be immersed in water for extended periods (not wet-moored in a marina), whereas Weldwood Resorcinol Glue is "waterproof."

Oxforddictionaries.com

On impervious definition the water resistant synonym got in there which I do not agree with but it is there.

You are right on plastic resin water activated vs resorcinol have used both.

[Dave M]

Yes, this is all great discussion; thanks for sharing!

I have also read elsewhere on Hydroracer that epoxy is not waterproof. I am as far from being a Chemist as one can be but I thought I understood the properties of epoxy at it applies to barrier coats. Can we explore this notion that ‘epoxy is not waterproof’ a bit further? Maybe there are different understandings of the definition of the word ‘waterproof’? Here is the first thing that came up when I googled it. In what way do we mean it does not meet that criterion?

Raymond,

I am going to try for a simple answer, without a lot of techie stuff. Not that I don't get it, but I realize most boat racers only need to know if they need to paint it or not.

West System, Epoxy, without any fillers to thicken it, and using the normal hardners and NOT the special coating hardner, is NOT waterproof. It is also NOT UV resistent. It needs protected from the elements and I don't care what some manual tells me. I have some experience in this and have noticed over time results.

Now then, you can purchase powders (fillers) and also a special hardner that adds UV protection and also some degree of water protection. When I say waterproof I am not saying the boat will leak on contact. If epoxy is exposed to water for a long period of time it will degrade at a much faster rate than if protected.It will also look like crap. I also believe that UV degrades it much faster than exposure to water. With this said, it is important to drain the water out before you load it in the trailer. If an open trailer, make sure it is drained before tarping or putting in the gararge.

[Yellowjacket]

Talking about the water resistance of epoxy is much like asking what the definition of "is” is... … And as our 42nd president answered under oath……. “It depends”….

Epoxy when properly applied to wood in sufficient thickness can make the wood sufficiently waterproof that it will not absorb enough water to result in rot. The problem is that it takes at least 3 coats of a good (high solids) epoxy to do that. Epoxy has a porous structure, and these pores don’t necessarily go all the way through the epoxy. By making the moisture barrier thick enough, wood can be effectively made sufficiently waterproof that boats left in the water will not absorb moisture and won’t rot. That’s close enough to “waterproof” for me. And note that the water resistance of epoxy is a lot better than things like polyurethane or polyester resins, so while it is not perfect, it is one of the best ways to seal wood against the damage that water can cause.

Most racing boat racing builders and owners are “weight-a-phobes” and are loathe to put any more resin on a hull other than what it takes to get a glossy finish, and this isn’t sufficient to provide much water resistance. So if you have had rot damage under an epoxy coating it’s more likely that there wasn’t enough of it there in the first place.

If you think about it, the amount of coating that it takes to provide decent water resistance is about the same amount needed to fill out a 4 ounce cloth, so why wouldn’t you use at least that much cloth in a coating since the cloth weighs almost nothing and the epoxy is there anyway? The answer is that most boat builders would rather take a bullet in the head than coat the bottom of a race boat with even 4 ounces of fiberglass cloth and epoxy because the end result they believe will be way too heavy.

(As an aside, if you look up the strength and weight of 4 ounce glass coated plywood, the strength and stiffness of 4 ounce coated 4 mm plywood is higher and the weight is the same as using 6 mm plywood alone, and you still have to “waterproof” or somehow keep the 6mm wood from rotting, so it is actually potentially lighter to make a hull out of thinner plywood and coat it with one layer of glass cloth inside and out and be stronger and in the end lighter than just using plywood alone.)

Since our boats aren’t stored in the water two coats of epoxy will keep the boat sufficiently dry that it should not rot so long as no water is left to stand in it and the boat isn’t covered while there is water still in the boat. The boat I restored was coated for 35 years with an automotive polyurethane, which would peel off if left under water for a few weeks, but it kept the wood pristine in the areas where it wasn’t damaged by cracking, so you don’ t necessarily need a super water resistant coating if the boat isn’t going to sit in the water all the time.

Boats that are not kept in the water, like our race boats are far more likely to suffer damage from UV rays so it pays to apply a coating to prevent epoxy from suffering the well know ravages of the sun. UV coatings, even those added to epoxies “burn out” over time and exposure to the sun. It was explained to me by an epoxy expert that after a few years of exposure the UV resistance essentially “goes away” and needs to be replaced so a varnish is a good way to do that. It’s a lot easier to strip off a varnish an recoat it than it is to grind off epoxy, even if it is old epoxy. About the time the varnish starts not to look good it should be replaced. Adding UV resistance to epoxy is a good thing, but it shouldn’t be the first line of defense. As it was explained to me if you just use a UV resistant epoxy it will last a longer than if it wasn’t UV resistant, but it won’t last forever and it won’t protect the stain or wood under it after that. If you want it to last a long time, varnish it with a good highly UV resistant varnish, maintain the finish, and it will last forever.

[ZUL8TR]

QUOTE "(As an aside, if you look up the strength and weight of 4 ounce glass coated plywood, the strength and stiffness of 4 ounce coated 4 mm plywood is higher and the weight is the same as using 6 mm plywood alone, and you still have to “waterproof” or somehow keep the 6mm wood from rotting, so it is actually potentially lighter to make a hull out of thinner plywood and coat it with one layer of glass cloth inside and out and be stronger and in the end lighter than just using plywood alone"

The builders probably do not want the extra work to do the cloth/resin coats/leveling etc over and above simple resin coats on the thicker ply. I think a little extra structure weight in the right places is better than not enough or the bare minimum and it just might let you finish the heat and the weekend.

[Will.Smoot]

Epoxy doesn't have a "porous" structure. It's a cohesive matrix of cross-linked organic molecules, making it waterproof and chemically resistant to most solvents and chemicals by nature. You're absolutely right in that there needs to be sufficient thickness in order to get the waterproofing, and good stuff the rest of the way. Enjoying the discussion.

[Yellowjacket]

My poor choice of words, I guess I should have used "permeable" and tried to explain it that way...

[Will.Smoot]

No worries! Just sharing the knowledge. Good discussion.

[Smitty]

Now wait, you say that epoxy resin, while permeable enough that you don't want to have any water in your raceboat when you put it on the trailer with a cover over it, is "a lot better than" polyester resins. But there are tens of thousands of boats moored permanently in marinas that were laid up with polyester resin. They are protected on the outside with a gel-coat (itself polyester resin) (and I know there are better and worse materials for avoiding blistering), but not inside, and no doubt lots of these moored fiberglass boats have water sloshing in the bilges from leaky seals and such. Are you saying that this water is being absorbed relatively quickly, wicking its way along the strands of glass, swelling the layup, adding weight, etc., etc.? I haven't heard of ordinary production pleasure boats being built with epoxy/glass to avoid this problem. Tell me more about it, Yellowjacket and Will.

[ZUL8TR]

Smitty

I agree with you on the longevity of fiberglass boats properly laid up. I have owned a few and repaired many and never noticed problems with the fiber glass polyester resin materials. Usual fiber glass repairs were due to hitting docks, beaching in sand and that sort of thing but never delamination or blistering.

Here is as interesting report with scientific data to support the longevity of fiber glass polyester construction. No wonder more expensive epoxy is not being used instead of polyester resin. Plus it sets quicker so construction is faster and adaquate strength can always be designed in for the materials being used.

http://www.ericgreeneassociates.com/..._Longevity.pdf

[Will.Smoot]

The word permeable doesn't fit into the equation either. Catalyzed resin systems (Vinyl/Polyesters) have a different curing mechanism and chemical structure as opposed to epoxy but both categories of marine coatings create cohesive matrices that, when a sufficient build thickness is reached, provide water proofing. Water will find its way in if it can, which can cause voids, delamination, and failure etc.

[Smitty]

If it is neither permeable nor porous, why does it need any particular build thickness? One would think if it is actually an impenetrable, insoluable-in-water substance, say like Saran wrap, it would be so with just a single application, a single coat, as long as it was free of porosity from intrained air, and had no dings in it. I'm not arguing with you, I'm just trying to understand why it should need multiple coats, or varnish, to seal the wood beneath. This is apart from UV degradation, a different thing.

[Will.Smoot]

Hey not a problem don't mind at all. I can explain it like this: Lets say if you just put a single coating of epoxy/resin on your wood decks, which are porous and breathable, you will get liquid absorption of the epoxy into the wood which may or may not leave very small exposed sections or pores where water can still get in. By building sufficient coats, you build up the coating past the wood and have pure epoxy providing a barrier between the substrate and water. hope this helps.

[guedo499]

Will Smoot = Dr. Smooth

[Smitty]

Doh, shoulda thoughta that, it makes immediate sense. In fact, it especially makes sense today, with the rather soft, punky, new growth boat wood that's available as compared to the gaboon and utile of 45 years ago. Probably a major reason to encapsulate today's wood with epoxy is the gallonage of sealer and varnish it would absorb if you didn't . . .

Thanks for your patience, Will. That's often what it takes to get through to the elderly.