epoxy forums

Online Forums are the Bane of my Existence

An Epic Rant

My humorous take on the Social Media disasters called Technical Forums

By Bruce Niederer — GBI Technical Advisor

I’ve answered a lot of phone calls and e-mails in my 23 years here at Gougeon Brothers, Inc. Many of the questions are repetitive—that’s the nature of helping customers both new and old to be successful. Some are interesting—a few are downright fascinating. But I know it’s gonna be one of those calls when the first thing I hear is “I was reading in this forum last night about…”

DOH! (I try not to slap my forehead loud enough to be heard on my headset.)

Let me treat you to you a couple typical and oft-repeated exchanges. The names are changed to protect the innocent and the dull. The names of the forums don’t matter—the following exchange could appear in any one of them.



I have an old wooden canoe that I just stripped of varnish. I’m thinking of using a penetrating epoxy before reapplying varnish. Any opinions?

Seriously? Any opinions? I think there might be a comment or 10!


Penetrating epoxies are great as a primer—I use one often. My theory is that once the solvents have all evaporated, the epoxy that’s left is microporous. The finish, especially if worked into the surface (meaning lots of brushing) forms a mechanical bond as well as an adhesive bond to the epoxy, and the epoxy forms a better mechanical and adhesive bond to the substrate than the finish alone would.

Oh Johnny (sigh) you started out so well, sharing correctly that highly solvent filled epoxies are not good moisture barriers (see my article “Penetrating Epoxy: Legend or Myth?” in Epoxyworks 45). But then you drive off a cliff with theories of mechanical and adhesive bonding. Like all forums, there will be someone calling out any holes in your post—what I call “the slap down.”


Stagger Lee

Wouldn’t a “mechanical bond” and an “adhesive bond” be basically the same thing? I’ve heard of mechanical bonds and chemical bonds, but I’m left wondering what an adhesive bond would be. The whole idea of hot-coating (meaning applying a topcoat over an uncured, solvented system) always presents a few questions in that the evaporating (and quite strong) solvents may be incompatible with the topcoat being applied over them. I admit I’m not a fan of highly solvented epoxies and think a fair bit of the marketing hype is distorted B.S. But there are instances where I could see it as a viable primer for paint or varnish. However, if it was my boat, I’d absolutely wait for the solvents to evaporate completely before applying a dissimilar material over it. The manufacturer of your paint or varnish certainly wasn’t expecting you to apply it over something which was still leaching strong solvents. It is probably worth noting that priming with any diluted epoxy product most likely increase your potential for UV problems. It’s also likely to make the eventual job of stripping the boat down to clean, bare wood for future refinishing a lot more difficult.

Stagger Lee I love ya! You asked exactly what I would ask and it sounds like you know your stuff.

You picked up on his adhesion confusion. As you said, there are two types of bonding. Primary bonding (a chemical bond) is when the adhesive, in this case, epoxy chemically bonds to a previous, uncured layer of epoxy and cures together creating a single fused layer. A secondary bond (mechanical bond) relies on mechanical adhesion, or the ability to key into the substrate. Except for bonding to uncured or partially cured epoxy surfaces, all epoxy bonds are secondary bonds.

I’m not sure what you mean by saying that priming with diluted or solvented epoxy will likely increase the potential for UV problems, but everything else is correct and I’m good with it. But will Frankie and Johnnie recognize this or will someone else throw another monkey wrench into the fray?

Billy DeLyon

Actually, penetrating epoxies form a moisture barrier on wood. If they’re used as a primer and you poke something through the varnish topcoat and penetrating primer, water will get behind them. This will cause dark stains that are impossible to remove unless the coated surfaces are completely stripped beyond the epoxy-sealed wood. This is quite difficult as chemical strippers will not dissolve the epoxy barrier. Dry scraping is the only alternative as heat will not soften the epoxy either! I prefer to lay down a thinned coat of varnish as a primer and hot coat over it when it is dry enough to do so. Clear/white shellac can also be used as a primer and will dry enough to be varnished over in just a few minutes.

Billy, Billy, Billy, Billy. This reply is an exercise in contradictions. First thing ol’ Bill claims is that solvent-filled epoxy forms a moisture barrier on wood. Um…no! Didn’t Johnny already establish that it is not a good moisture barrier? Next Billy D. correctly states if water gets into the wood behind these coatings, the wood will get stained—which is actually the beginning of rot spores expressing themselves. Rot spores are always present in wood but they need sufficient moisture and air to start eating your wood.

Next, he says chemical strippers will not dissolve epoxy—correct. Then goes on to say heat will not soften epoxy—incorrect. Heat does indeed soften epoxy, but the epoxy portion of a highly solvented penetrating system is not on the surface of the wood, rather, it’s just beneath the surface of the wood.

Finally, I’m not one to argue with success, as my old pal Tom Pawlak was fond of saying. That said, I have not heard of anyone successfully hot coating varnish over varnish or varnish over shellac on boats. That’s an old technique I’ve heard furniture builders use, but they rub it on like a stain.

But wait, Johnny feels the need to defend his first statement against Stagger Lee’s slap down.


The mechanical bond I refer to is one where the paint works its way into the pores in the cured penetrating epoxy surface, then hardens. Some, if not most, of those holes will be bigger on the inside than on the outside so the paint will be mechanically locked in place.

That this is actually happening is just a theory I came up with to explain why the varnish did not peel as soon as it surely would have otherwise.

Adhesion is the molecular force of attraction in the area of contact between unlike bodies that acts to hold them together. This is not a chemical or mechanical bond, the two surfaces do not chemically or mechanically combine. Paint adheres to glass without any chemical reaction between the two, and unless the glass is sandblasted or chemically etched there will be no mechanical bond.

Paint/varnish can and does form a mechanical bond as well as an adhesive bond when it soaks into new wood, but the bonds formed between epoxy and wood are even more durable. That’s why we glue with epoxy rather than paint or varnish.

Anyway, it worked for me, and in my experience repairs always show as a different color, penetrating epoxy or not.

Huh??? Clearly, Johnny has a poor understanding of chemical, mechanical, and adhesive bonding. His idea that paint can work its way into the micro-porosity left by the escaping solvents and key in is just not possible. But Johnny is nobody’s fool— he concludes with the universal cover story in case someone actually calls BS on the BS he’s just been flinging: “Anyway it worked for me…”

Good one Johnny. Good one.

But Stagger Lee senses he has Johnny on the ropes so he starts working on the body.

Stagger Lee

I would certainly love to see some actual scientific tests/proof that this is even possible. Surface tension alone of something as thick as paint or varnish would keep it from “working its way” into nearly invisible small solvent pores.

Oh my. Stagger Lee delivers a—pun intended—staggering blow to Johnny’s mid-section. From where I sit, Johnny’s knees are getting wobbly.



I did say to rub it in with a brush you know, and if it were thinned it would work even better. I’d like to see that theory tested too, but I’m willing to accept my own experience as sufficient.

You’ve got heart kid, I’ll give ya that. But your theory is still wrong.


Stagger Lee

You really think you can rub paint into pores which are too small to even see in any meaningful way? Personally, I don’t, but whatever floats your boat.

Wham, Bam Thank You, Ma’am! A stunning TKO victory for Stagger Lee!

That’s my take on this exchange. In fact, there is a lot of misinformation in this thread and who knows what Frankie will take away from it? Another thing to consider is that Frankie originally asked about re-varnishing an old canoe and didn’t provide any more detail than that. It doesn’t sound like the canoe in question is a modern stripper built with epoxy and glass and with few, if any, frames. More likely, it’s an older canoe built with copper fasteners and lots of frames. Would it hurt if he were to use a penetrating epoxy as a primer, assuming he let it cure for a good 72 hours to make sure all the solvents evaporated, then sanded the surface before applying varnish?

No, probably not. My point is that forums are so often filled with any number of misconceptions, bad information and outright lies one must remain skeptical about what is said, and by whom.

Here’s one more quick exchange that expresses and repeats a long-held and widely believed misconception regarding gelcoat over epoxy—an oldie but goodie!



Just a quick question. I was thinking about taking off the rails that go around the bow. That’s going to leave a lot of screw holes that will be an eyesore, lol. What could I use to fill in those holes to make it not look so bad?

That seems to be a reasonable question. Let’s see what the forum world has to say.



3M™ 5200.

Yikes! Why would anyone want to use a soft urethane sealant material to fill visible holes in a deck?

Let’s just ignore this yahoo and move on.



In addition to 3M 5200, you could use a 2-part epoxy (e.g, PC-11, Marine R/X) or you could fill them with some sort of thickened polyester resin followed by a top coat of gelcoat. The easiest would be 5200 or epoxy. Resin/gelcoat would give you the option of trying to color-match the boat so the repairs are less obvious.

Holy Bat Guano Batman! Two of them in the same thread! Marine R/X over 5200? That’s some particularly bad advice right there. It’s just…stunningly wrong! Is there any hope for this thread?



If you are concerned about appearance, I would fill with epoxy to just slightly below the surface and top coat it with matching gelcoat.

Now you’re just showing off Magellan! First, you organize the whole first circumnavigation of the world—and now this. You hit the nail on the head in one simple sentence that actually helps Marco. Sweet!


I was under the impression that generally, gelcoat doesn’t adhere very well to epoxy.

Marco. Hey, all my props to ya brother. Exploring China and bringing it to the world through your writing…nothing but respect. Seriously. And you’re a lot of fun in the pool too. But let’s be honest, Magellan did the whole around-the-planet thing. I would advise you to concede this one to Magellan.

All kidding aside, we get this I know gelcoat won’t stick to epoxy comment often. So here’s the real answer concerning gelcoat over epoxy—there are three conditions that must be met to successfully apply gelcoat over epoxy:

First, the epoxy resin and hardener must be mixed at the correct ratio.

Second, it must be completely cured. If the epoxy is applied at low temperatures it may need to cure for a few days. 48 hours at 72°F is the standard to aim for.

Third, blush must be removed if using 205, 206, or 209 hardeners. 207 is a blush-free hardener.

If you meet these three conditions, you can successfully apply gelcoat over epoxy.

In fact, there is a WEST SYSTEM video showing how to properly apply gelcoat over an epoxy repair. It features Joe Parker, a (now retired) employee here at GBI, rockin’ his ‘80s haircut.