Marine plywood grades are only half the story
When buying any plywood, it is important to think about what you are building and what functionality is most important. This is especially the case with marine construction as marine grade plywood is a term that gets used a bit too loosely and not all of it is created equal.
The things to consider with marine plywood are:
- Species
- Grade
- Weight
- Bending ease
Certainly there can be more factors to look at but the above will guide you to determine if a particular product is right for you and your specific needs. In general marine grade plywood will have no voids in the core and minimal repairs (football patches) to the faces of the veneers. A water and boil proof (WBP) glue must be used and this is usually either a Melamine or Phenolic resin glue. Right away if the particular panel you are looking at uses a different face veneer from the core, it won't be a good quality marine panel for boat building. But again this is where your particular needs will dictate what to buy. Are you building for exterior construction or actually building a boat where the plywood will be submerged and stay in contact with water for long periods of time? The answer to this will immediately change the products and manufacturers you should be looking at for plywood.
For boat building, plywood selection should be a paramount concern. It will be expensive, no doubt. For the hobbyist and small boat builder it can be a sticking point. But good quality material will make that boat last a lifetime and only the finest materials can be counted on to perform in such harsh conditions.
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Nice episode yet again.
Regarding your reference to Shou Sugi Ban and the vikings, i have a question. The black buildings you are referring to here in Norway, are you sure you are not confusing charring with tarring? Tarring is an old tradition here in Norway. You can see that on the stave churches from early medieval times. They are dark blackish brown. But the colour comes from tarring, not charring.
This is a good point and perhaps I’m mistaken many of the black buildings I see as charred. I do however know that some burning tradition exists in northern Europe and Scandinavia. Perhaps I am mistaken in attributing it to Vikings or even Norway. Thanks for bringing that up.
As Are pointed out, tarring of buildings is an old tradition. When it comes to burning traditions in Norway, I found a couple of sources claiming that burning was used on dock posts and fence posts in olden times. The veracity of this I can’t confirm as there is no reference to what source the claims come from.
As an offshoot (or an digression) of burning, a local man was restoring an old house a few years ago. And the conservation authority mandated that he use old growth pine (known as “malmfuru”, I don’t know the English translation. The point is that the pine is old growth, often at higher altitudes, and the natural resin of the pine has saturated the center of the tree.) for cladding. The cladding is then left untreated (!) and the sun and weather is supposed to do the surface treatment of the cladding. It’s a well documented tradition, and the cladding can stand up to the weather for several hundred years, at least where there is a drier climate.
“Malmfuru” was also used in stave churches like the one in Urnes, dated to around 1140. Fun fact: The oldest dated log in the church started to grow in 765.