marine plywood to place seats

[capslock118]

My local lumber store sells 4x8 "AB Marine Fir Ply' - 4x8

1/4" for $49
1/2" for $70
and 3/4" for $88

I have to replace the wood for my rear seats soon. At the very least the wood for flooring of the base of the seats need to be replaced. It's all flaking apart and soaked with oil from over the years holding an oil reservoir.

Questions:
I would think that I would want 3/4" to support seats?

Is there any post-work that I need to do before installing this plywood? I.e. does it need to be sealed or the fact that it is marine ply imply that it is already sealed?

Do you know what AB means in the name of the plywood?

 

[bananaboater]

Re: marine plywood to place seats

Questions:
I would think that I would want 3/4" to support seats?

Is there any post-work that I need to do before installing this plywood? I.e. does it need to be sealed or the fact that it is marine ply imply that it is already sealed?

Do you know what AB means in the name of the plywood?

Yes, I would use the 3/4 and seal it with epoxy. And any holes drilled afterwards need to be sealed with 3M marine sealant.

AB refers to the quality of the wood on the faces. A is high quality supposedly without knots and B has knots. For instance on house roofs a BC grade is used, just as strong but looks ugly.

 

[Bondo]

Re: marine plywood to place seats

Ayuh,... Most seats are made of 1/2" plywood that I've seen,...
Both bases, 'n seatbacks...

Personally,... I wouldn't waste the money on Marine ply,... It's made the same as Ext. ply,...
Maybe a few less internal voids, but who cares, it's a Seat...

The AB is the grade of the faces,... A is the clearest,... D is the roughest...
So, your AB is 1 side about perfect, 'n the other darn near perfect...

I use CDX,.... That's rough 1 side, 'n rougher the other, Exterior glues...
It's a Seat, 'n will never be seen...

As fer Sealin' it,... No, it don't come that way, regardless the grade,...
It's Your choice,... paint, glass, resins, oils, etc....

 

[capslock118]

Re: marine plywood to place seats

Personally,... I wouldn't waste the money on Marine ply,... It's made the same as Ext. ply

So i've read this in multiple threads here since I posted this.

I'll probably take the route of buying PT or regular ply and then seal it to keep costs down. The way I did the math I could rip out the entire boat and replace floor and the seats for the price of what I would need just for the seats in marine grade.

Most seats are made of 1/2" plywood that I've seen,...
Both bases, 'n seatbacks...

Yes, I would use the 3/4 and seal it with epoxy. And any holes drilled afterwards need to be sealed with 3M marine sealant.

On a related note, what are the recommendations for flooring? Specifically, the fuel tank is built-in and the floor above it is a bit weak and sags when stepping on it. Further the flooring underneath the seat which needs to be repaired the most (and where this project is coming from) appears to be the flooring for the rest of the boat - so this might be a larger project than I initially anticipated.

Something like this work?
1/2 in. 4 ft. x 8 ft. CDX - ACQ Treated Plywood

 

[alldodge]

Re: marine plywood to place seats

Main difference between marine and treated plywood is marine is pre-dried. I wouldn't seal or lamanate treated plywood, just asking for trouble.

 

[Tail_Gunner]

Re: marine plywood to place seats

Ayuh,... Most seats are made of 1/2" plywood that I've seen,...
Both bases, 'n seatbacks...

Personally,... I wouldn't waste the money on Marine ply,... It's made the same as Ext. ply,...
Maybe a few less internal voids, but who cares, it's a Seat...

The AB is the grade of the faces,... A is the clearest,... D is the roughest...
So, your AB is 1 side about perfect, 'n the other darn near perfect...

I use CDX,.... That's rough 1 side, 'n rougher the other, Exterior glues...
It's a Seat, 'n will never be seen...

As fer Sealin' it,... No, it don't come that way, regardless the grade,...
It's Your choice,... paint, glass, resins, oils, etc....

Very much in agreement..I just seal them up with CPES (Clear Penetrating Epoxy Sealer). followed bedliner spray..Half inch plywood glued and braced is very strong...3/4" is over kill

 

[oops!]

Re: marine plywood to place seats

hi all.....


im seeing a number of misconceptions here that i will try to clear up....

bondo and tail gunner have it correctly short tracked.

the marine wood vs ext grade ply are well documented on this forum.....but in short....
marine has less/no voids between the layers of ply (this is important ONLY if you are building a wooden hull boat)
it is dryer...(that is nice)
most importantly the glue used in marine is waterproof.

exterior grade plywood also has the waterproof glue we need and is very inexpencive and readily available.

the treated wood you were looking at is great....however pressure treated wood is very wet (even tho it seems dry) and needs about 6 weeks minimum to properly dry out before you can fiberglass it.

the regular exterior grade is wet also and will need to be dryed with a fan and heat for about a week minimum.

(you even need to dry marine ply for this amount of time)

you were saying that the deck is soft by the gas tank and under the seats.

you need to investigate more......these are warning signs that your stringers are also rotten....the deck is uasually the last to go.

decks are uasually 1/2 inch thick plywood with 1 oz fiberglass under them and 8 oz on top.

however......over top of a gas tank there are uasually recesses cut into the stringers where an additional 5/8 ths ply is above the gastank then the 1/2 inch over that.

under seats......if they are standard back to back or bench loungers.....the 1/2 inch is fine. however if they are pedistal seats......you will need some more reinforcement under the pedistal base....this is uasually a 1 foot sq piece of 5/8ths under the deck where the base is.

i can tell from your post that you will need to do much more inspection on your boat....in fact you wont know the full truth untill you have the deck off the boat.

whatever the condition is....it can be fixed quite easily with a little bit of elbow grease and a lot of time.

good luck
oops

 

[kmarine]

Re: marine plywood to place seats

As a marine upholstry shop owner use exterior grade plywood. I use 1/2" to keep the weight down and pollyurethane wood glue to glue and reinforce corners with 3/4" plywood. do not use traeatd plywood. it is too wet and does not glue together nicely. Then you can epoxy coat, polyester coat or just paint the completed frame with latex paint depending on weather exposure. All you really need to do is protect it from moisture. Use marine plywood on the deck and be sure to use resin or epoxy. Many boats use the deck to support stringers.