There's a lot of noise about ONLY using marine plywood for watercraft.
Yeah sure... if you're building a boat that lives 365 days a year in the water then most definitely use the lightest and best marine plywood you can afford... that's what I would do if my wife ever let me build a boat.
But selecting plywood for a stand up paddle board build is a bit of a grey area as the board doesn't spend its life permanently immersed in water. A stand up paddle board only sees water when it's in use, so unless you intend to paddle across an ocean for several months on end you can afford to expand your plywood choice horizons.
The similarities and differences between marine ply & exterior ply
Before we get into the details of what separates these plywood cousins, it’s important to acknowledge their similarities. The most obvious similarity is that both Marine Plywood and Exterior Plywood are designed to be used externally.
Both plywoods utilise an A-bond glue, allowing them to stand strong in the face of all the unique challenges that come with being used in the unpredictable outdoors. The A-bond glue must be Weather and Boil Proof (WBP) which means the glue has been subjected to boiling water for more than an hour without delamination of the plies.
The differences between marine ply and exterior ply are the quality of the piles or veneers, specifically the BS1088 marine ply standard does not allow ANY voids in the inside veneers. All marine plywood will be free of voids in the core. Voids are traps for water and will rot the product from the inside out. Exterior grade plywood is not subject to such strict guidelines and could potentially have small voids in the inside piles.
Thoughts on marine vs. exterior ply for stand up paddle boards
Here's my two cents on considerations think about when selecting plywood to build your board, in order of most relevant to least relevant...
- What plywood do you have access to?
- What's your budget?
- How light do you want to build the board?
- Where are you going to store your board?
- How do you want the board to look?
Let's do a really quick dive into each point...
What plywood do you have access to?
Depending on where you live you may only have have a very limited choice of plywood available. If you live in a remote area or a developing nation you may not have access to the best quality marine plywood or even a good quality exterior grade plywood, or the cost of shipping the plywood from a retailer may be prohibitive.
What is your budget?
Not all of us have the unlimited resources to buy the best marine plywood at premium prices. I've seen some eye-wateringly expensive numbers quoted for marine plywood, but on the flip side a good exterior grade ply can be as little as 25% of the cost it's much touted big brother. If you're budget is tight exterior plywood is a sensible option.
It's important to remember though, the total cost to build one of our boards, even when using 3 sheets of quality marine plywood, is still far less than buying a similarly sized production board.
To keep my design development costs down I'm thinking about building a board completely from recycled old door skins which could save over $300 in plywood. I've had a quick look online and found a decent selection of doors that are either free or very cheap and would be perfect for a paddle board. I'm looking forward to trying this out.
How light do you want to build the board?
For this point, marine plywood wins hands down as marine plywood can be as much as 30% lighter than its exterior grade cousin. If you're goal is to build the absolute lightest possible paddle board then you better stump up the cash for the good stuff!
The first board two boards I built were out of exterior grade plywood, I only started building in marine plywood to make an accurate weight comparison, here's the weights for a Cutwater 12.5 built out of exterior grade plywood and marine plywood. Not much difference!
Are you going to store your wooden board inside or outside?
If you're crafting your own stand up paddle board from wood chances are you're going to look after it and keep it inside out of the elements but this may not be the case for everyone.
Marine plywood with its complete lack of voids will definitely endure more punishment from the weather than an exterior grade board. But, from my experience, exterior grade board's are slightly stronger and can handle more knocks and bumps than the lighter marine plywood board can.
The key factor for a board's ability to stay dry and rot free is how it is built and sealed. A very well made exterior grade board will last longer than a poorly built and sealed marine ply board.
How do you want the board to look?
This point is last as it's purely an aesthetic decision but one worth discussing all the same. Exterior grade plywood is generally made from Pine or Douglas Fir a lighter coloured timber when compared to the deeper tones of Okoume (also know as Gaboon).
If you're looking for a rich & traditional Mahogany coloured board choose marine plywood, if you're not fussed you can go with exterior grade plywood.
Remember pine tends to yellow a little in the sun so keep the board in the shade if you don't want this to happen.
Final thoughts... it's about the paddling not the building
If you have access to a reasonably good 3mm plywood that has few voids and isn't too heavy then buy it before someone else does and get building! If you want and can afford the best possible plywood go with marine plywood.
Remember.. either way it's about the joyful feeling of paddling your own hand built board.