Marine Grade vs. Exterior Grade Plywood

What is the deal with marine grade plywood? 

Having a hard time figuring out if you really need to pay the premium and use "real" marine grade plywood for the interior of your sailboat? Me too!

During the last couple of weeks I've spent some time trying to figure out what to do in my 1973 Albin Ballad. Why bother with all this and simply not just pay the premium? Firstly, I'm curios. Secondly, in Denmark there only seems to be one supplier of BS 1088 marine plywood. Not surprisingly their prices are a bit high. 340 USD for a single sheet (16 mm). Keep in mind, that price is for okoume and not anything fancy like teak or mahogany. Seeing as I need about 15-20 sheets a bit of digging seemed like a good idea.

What IS marine grade plywood?

Often you see the term "BS 1088" when looking for marine grade plywood. So what does BS 1088 mean? First things first. BS 1088 is, or should i say WAS a standard. BS 1088 is short for British Standard 1088. The standard is associated with Lloyd's of London. Technically, Lloyds is no longer offering the BS 1088 certification standard. It has been an industry standard for long enough to serve itself therefore the term is still in use.

BS 1088 plywood needs to fulfill certain criteria. Primarily that there are no voids between the plies, that the glue is WBP and the thickness of the face veneer. It is important to know that there is no longer anybody that polices the standard. This, in my eyes, means that you need to find a reputable provider that you can trust. Joubert Plywood seems to have a good reputation. Too bad I can't seem to find anywhere to purchase their products in Denmark.

The glue that binds us

A lot of exterior grade plywood is made using the same glue as marine grade plywood. The stuff is usually called WBP (Water Boiled Proof). I've also seen it referred to as EXT although I don't know if that was a mistake. It goes without saying that using a glue that can withstand water is a must. But keep in mind that although the glue can withstand water the wooden plies can't. Whether you use marine grade or non-marine grade plywood using epoxy or varnish/lacquer to preserve the wood is paramount!

What's the difference?

From what I've been able to find out, not much. That being said do you really want to take the risk something like bulkheads? I'm still not convinced that I need to use plywood labeled as BS 1088. I will be sure to post a blog entry when I do make a decision.

Plywood used in the Albin Ballad

I see a lot of lower grade plywood. When I say lower grade I'm referring to the thickness of the face veneer and thickness of the core plies. The only thing that appears to be strong plywood (many thin plies vs fewer thick plies) are the bulkheads. I'm not surprised that the bulkheads are a better grade than the rest of the interior. Keep in mind that I'm a complete novice and that the interior of this boat has held together for 40 years. Albin must have know what they were doing ;)

Need more information about BS 1088?

As often is the case Wikipedia is a great source. http://en.wikipedia.org/wiki/BS_1088