“Isn’t Marine-Grade OSB an Oxymoron?” – Letter from a Reader (He’s Right)

Hello there! In my Questions From the Road column, I take a crack at answering real questions from real RVers, just like you. You might find your question here! If not, please send me an email!

Engineers don’t have a Hippocratic Oath, per say, but the National Society of Professional Engineers does publish a Code of Ethics for Engineers. Among other mandates, it states:

  1. Hold paramount the safety, health, and welfare of the public.
  2. Perform services only in areas of their competence.
  3. Issue public statements only in an objective and truthful manner.

I may not have raised my right hand and sworn on the Bible to accept these oaths, but I do abide by them (I’m not a PE). When I started this blog, I knew that before the Google algorithm, before views, before advertising, before anything else, came command #3: Issue public statements only in an objective and truthful manner.

Recently, I received an email from a gentleman named “Thomas” who had read another letter from “Martin” about the faulty claims made by RV manufacturers about 4-season performance. Thomas had his own bone to pick: the claim of “marine-grade OSB.” 

I’ve copy-and-pasted our conversation below with some editing for brevity and clarity. In my research to answer his question, I had to wrestle not only with science but with ethics. When does industry jargon turn into Orwellian newspeak? If we’re going to improve this industry, maybe words should come before design?

Thomas Writes: Isn’t Marine-Grade OSB an Oxymoron? 

“I have read some of your posts including the most recent one. I really agree with Martin. I have worked in the RV industry … and I have worked in custom home construction.

“I believe that all of the RV industry misrepresents and many manufacturers knowingly commit fraud in materials science. I am suspicious even with one of your posts where you refer to marine OSB.

“A very popular recent manufacturer where I was would tell concernés customers in-person, maybe not in print, that their OSB was marine grade, also. An engineer who does custom homebuilder work laughed at this when I asked about it and said I should give him the grade coding for it and by which association because he has never heard of it or seen it and thinks that is straight-up fraud. What is it by industry grading that you RV types refer to by that term?”

P.S. The article Thomas referenced was my post, “Wood Vs Aluminum Framing in an RV – Which Is Best?” And I also used the term “marine OSB” in my post, “The Textbook Treatment – RV Subfloors and Leaks.” 

Andy Replies: Hmmm … Good Point! What’s the Basis for These Claims?

“I love, love your question! As a writer, I know how important language is. I’ve always heard RV subflooring OSB subflooring referred to as “marine OSB,” so I’ve parroted the term. Hmmm … I should have been more skeptical!

Obviously, you wouldn’t want to use OSB on a boat; I speculate the term is derived from the fact that the panels are built with a waterproof “marine-grade” adhesive, not that the OSB is actually suitable for boat building.

I often use industry-accepted terms in the interest of clarity. However, I don’t want to use terms if they cause confusion or may mislead people. Your email has made me rethink the use of this term, even if it is “accepted” in RV manufacturing. 

Your question has led me down a rabbit hole … I’ve reached out to a few OSB panel manufacturers and have asked them A) if they’ve ever marketed these products specifically for the marine industries and B) what APA or ICC ratings do these products carry. 

I expect to confirm that no, these panels are definitely NOT rated for marine use, and what’s more, they really aren’t designed for long-term exterior exposure of any kind. And they aren’t guaranteed void-free like marine plywood. To my knowledge, even the best subfloor on the market, AdvanTech, only carries on an Exterior 1 rating. 

Again, Thomas, thank you for bringing this to my attention.”

Thomas Responds: And Bad Answers Keep Coming from the Factory Tour Guides!

“Thank you for checking. I kind of knew it was impossible and a lie when the engineer laughed. I like the idea of RVs but I think those who own most of these factories, especially the technical and marketing parts, can’t self-regulate. They need basic good rules and enforcement.

“I’m sorry but look what happens! (One reason for sure why the person in your blog said the factory tour was a joke for any engineer). The person assigned to the tours will stupidly answer this [marine-grade OSB answer] to anyone who questions the OSB as a bad idea … Imagine a building science guy being told, “Oh no, it’s marine grade.” Think someone would be embarrassed??? 

“Trying to get retired couples to spend a lot of their life savings for units built like this by literally lying to them and in front of other people – and it’s not just the low end.”

Andy Responds: It’s As You Feared …

As I promised to Thomas, I spoke to a few OSB panel manufacturers and researched the Technical Data Sheet for several OSB panels: Huber Woods Performax OSB, Georgia-Pacific Dry Max Sturd-I-Floor, Weyerhauser Structurwood, and Tolko T-Strand. 

Here’s what I found:

  • I found no sales literature advertising these OSB products to the marine industry for use in boatbuilding. Nor did I read in any warranties that these OSB products were rated for marine use. In fact, one OSB panel manufacturer told me straight up, “We do not manufacture any products that are intended to be used in boatbuilding.”
  • Most OEMs claimed their OSB products were certified or analogous to the APA or TECO PS 2 standard, which is the Performance Standard for Wood-Based Structural-Use Panels. This is mainly wooden siding – again, not for nautical use.
  • Similarly, all the OSB products I researched were rated at Exposure 1, which is NOT permanently waterproof. Exposure 1 panels are “intended to resist the effects of moisture due to construction delays or other conditions of similar severity but not long-term exposure to weather.” Contractors call this the “dry-in period.”

Here’s the thing: Exposure 1 is primarily a glue bond specification. They aren’t rated for long-term exterior exposure. In the case of OSB, it can’t be rated for long-term exposure because repeatedly wetting and drying OSB causes it to swell and disintegrate. I wonder if “marine OSB” was originally shorthand for “OSB made with marine-grade glue but only rated for short-term exposure”? And somehow the salient second half got dropped? 

But at this point, the granular details don’t matter. Thomas (and his engineer) are right: For all practical purposes, there’s no such thing as “marine OSB.” Yes, some “premium” OSB subfloors are manufactured with resin-sealed edges and waterproof overlay layers, and while those are good things, to call them “marine-grade” is a misnomer. You wouldn’t use them on the boat, and if they get wet repeatedly, they fail.

Which reminds me of a side note: You will see some flooring materials marketed as “waterproof” because a sample of the floor is stored in a clear jar half full of water. This is mostly a sales gimmick. It is the repeated wetting and drying of OSB (and all the bacteria inside dirty water) that causes the most damage, not merely being immersed in water in an airtight container.

So thank you, Thomas, for holding me accountable. I’ve removed all mentions of “marine OSB” from my website. (And who says engineers can’t admit when they’re wrong?).

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