Wood over wood?

[drev500]

I am going to be reflooring my boat over this winter and saw someone use cedar planks. I loved it. Currently, all of my floor is pulled so I was going to lay plywood down (marine grade or glassed over plywood). I have a Starcraft Holiday with 2 aluminum stringers going bow to stern. Can I lay the plywood to give me the base/ structural layer then lay the cedar over it? My thinking is the layer between them would allow moisture to build up?

What I was going to do was lay plywood and fasten to the stringers and side. Then lay adhesive and lay down cedar planks (I would stain them beforehand). After laying down the planks, I would apply a couple of layers of epoxy to seal/protect (sanding in between each layer). Am I thinking correctly?

 

[BRICH1260]

While I`ve never seen it done, I don't know why it would not work. I would make sure that the subfloor was watertight and maybe leave an airgap between the planks so that they did not hold moisture between the cedar boards. Your plywood and backside of the cedar plank could be subject to rotting quicker as any moisture that gets caught between the two will be trapped.

 

[GA_Boater]

Is this the boat you plan on converting to jet drive? Extra weight won't be your friend whether you convert or not.

 

[Chris1956]

I would think that the floor would need to be waterproof, so use the plywood as a deck and put a couple layers of glass and resin over it to seal it. For appearance, you could add the cedar, but since you do not need any strength, you could use thin strips of cedar. Stain and finish them and then install them. Adhesive for the install sounds about right. Use a marine-grade urethane over the cedar, as that will protect from the sun.

Do you have foam between the stringers?

 

[smokeonthewater]

Skip the plywood.... Lay oak boards crosswise on maybe 12" centers and then strips lengthwise with minimal gap... Fasten with brass or stainless screws.

 

[Grandad]

Drev, I can see a few issues.
Even if a product can withstand moisture (eg plastic), if it is contoured (grooved?) such that it can trap moisture in any way, it's a negative in a boat.
Cedar looks nice, but is soft like pine and will dent easily and you won't be able to maintain any solid seal on the surface.
If you laminate the cedar to the plywood with adhesive and decide it was a mistake, it'll be a heck of a task to remove it as a monolith or in pieces.
The total thickness equivalent to 2 floors is unnecessarily heavy for a boat, though it will help float your boat if it's submerged.
- Grandad

 

[pckeen]

I'm a furniture maker, and work with solid wood all the time, both inside and outside. I see several potential problems. Regardless of how well it is sealed, a solid cedar floor will move with the weather. The cedar will contract and expand, particularly widthwise, so you will need to build in places where the wood can expand and contract. The cedar, as it gets wet and dry, may warp with age. If you install it over a wooden sub-floor, you will be creating a tiny gap with the two layers of wood in contact - this will trap moisture and rot. If you do build in an airgap, you will need a framing system over the subfloor, which will make your floor thicker than before. In addition, adding two layers of wood will add considerable weight to your boat.

So if you are going to do this - ditto on the comments above - do a single layer of wood, not two layers. Don't build the floor flush with the sides of the boat, as when the boards expand - they will need somewhere to go.

With completely wooden boats - they literally expand and contract with the seasons, and boats should be built in a manner that takes that expansion and contraction into account. But with a boat that is both solid wood and non-wooden, the solid wood will expand and contract in a very different manner than the rest of the boat.

 

[jigngrub]

Skip the plywood.... Lay oak boards crosswise on maybe 12" centers and then strips lengthwise with minimal gap... Fasten with brass or stainless screws.

Brass, copper, and bronze have no place in an aluminum boat. Just a single small filing will eat a hole through an aluminum hull or gas tank.

 

[jigngrub]

I am going to be reflooring my boat over this winter and saw someone use cedar planks. I loved it. Currently, all of my floor is pulled so I was going to lay plywood down (marine grade or glassed over plywood). I have a Starcraft Holiday with 2 aluminum stringers going bow to stern. Can I lay the plywood to give me the base/ structural layer then lay the cedar over it? My thinking is the layer between them would allow moisture to build up?

What I was going to do was lay plywood and fasten to the stringers and side. Then lay adhesive and lay down cedar planks (I would stain them beforehand). After laying down the planks, I would apply a couple of layers of epoxy to seal/protect (sanding in between each layer). Am I thinking correctly?

As others have mentioned:
1. Cedar is pretty soft so you would have to be careful with heavy stuff in the boat.
2. The planking will need to be able to expand and contract, but that's not a big problem.

I would skip the plywood decking and install additional aluminum angle framing to accommodate the cedar planking.

I would use the 1x6 tongue and groove exterior grade cedar siding boards, like this:


You will need to leave a 1/4"-3/8" gap around the 4 sides of the planked area, cover this gap with an aluminum angle trim.

For fasteners use either stainless steel screws or aluminum blind (pop) rivets. I personally like the looks of the exposed rivets in an aluminum boat. When spaced evenly and in a straight line they enhance the beauty of the finished decking.

Epoxy resin isn't UV stable so you would be better off using an exterior grade spar urethane or marine varnish. this will make the deck slick when it gets wet so you need to wear gum rubber deck shoes in the boat.

The biggest drawback I see to all of this is expense, aluminum angle isn't cheap and cedar siding is expensive! $10-$12 for a single 1"x6"x8-10' board... but! it will look really nice when you're done with it and will be something you don't see every day in a boat.

 

[robert graham]

If you like the look of cedar then consider cypress with urethane finish.......you would need the urethane finish in the boat to protect the wood and leave a nice walking surface and the look would be great!....it's very rot resistant wood!...

 

[gm280]

I've read all the comments and my feeling (opinion, for what that's worth) is, don't do it. While it would look nice, I can see you replacing the floor in maybe a year if it sees a lot of weather/water. There is virtually no way to seal cedar wood laying on top of exterior plywood from holding water. It simply can't be done. You could dip the cedar planks in plastic, but the first ding or dent on such a soft wood will be the entrance for water, and from there it is rot. And there will be water sitting between the plywood and top cedar planks. It is the nature of the beast. But this is just my opinion and we all know about opinions... :facepalm: