Joining plywood

[sawmill]

I am going to be joining some plywood along the 8 foot side to make the sheet wider. I was going to use biscuts and glue or does someone have a better way. I am thinking of maybe a half lap joint. This is a floor in a boat so it has aluminum stringer every 8 inches or so. Just looking for some ideas

[jsburger]

I am going to be joining some plywood along the 8 foot side to make the sheet wider. I was going to use biscuts and glue or does someone have a better way. I am thinking of maybe a half lap joint. This is a floor in a boat so it has aluminum stringer every 8 inches or so. Just looking for some ideas

Well, it is also known as a ship lap.

[algale]

With any luck Shipwright will pipe in on this subject. Otherwise, you should PM him.

[masonsailor2]

Are you going to resin the plywood after ?
Paul

[masonsailor2]

If you use #20 biscuits and place them close together and use a good marine glue it will exceed the strength of the plywood.
Paul

[BuckeyeDennis]

Tongue and groove joinery is the typical method for plywood subflooring - you can buy it with the T&G already milled. If you are using a specialty plywood, it's easy enough to mill the T&G with a router bit set. If you optimize ply grain directions and tongue thickness, the resulting joint will likely be stronger and stiffer than even a continuous row of biscuits.

[reible]

Tongue and groove joinery is the typical method for plywood subflooring - you can buy it with the T&G already milled. If you are using a specialty plywood, it's easy enough to mill the T&G with a router bit set. If you optimize ply grain directions and tongue thickness, the resulting joint will likely be stronger and stiffer than even a continuous row of biscuits.

I know nothing about this for boating applications but it certainly works in homes. Now having said that I have seen the pieces crack due to it being plywood so seams should be supported as best you can what ever joint you pick.

I also wonder what effect the heavy moisture would have on standard flooring, and if it would be subject to getting soaked every once in a while.... Marine plywood could be a better answer?

Ed

[Hobbyman2]

What about a floating tenon?

Use a trim router and cut a 1/8" grove down the center of the pieces say 1/4" deep , then glue in one solid long piece of hard wood strip just a little under 1/2"w x 1/8" thick to join them ? " tong and grove" ,,Marine plywood ,,,,I have done this on a old restoration years ago ,,, also fiberglass on both sides and all edges of the flooring will help keep moisture out .

I drilled 3/8 holes in locations and filled the main cavities with expanding foam once the floors were in ,,,, every now and then a few 1/2" holes to allow the foam to expand ,,trim it off after it dries,,,,except the center of the boat , I left it open for drains.

[sawmill]

What about a floating tenon?

Use a trim router and cut a 1/8" grove down the center of the pieces say 1/4" deep , then glue in one solid long piece of hard wood strip just a little under 1/2"w x 1/8" thick to join them ? " tong and grove" ,,Marine plywood ,,,,I have done this on a old restoration years ago ,,, also fiberglass on both sides and all edges of the flooring will help keep moisture out .

I drilled 3/8 holes in locations and filled the main cavities with expanding foam once the floors were in ,,,, every now and then a few 1/2" holes to allow the foam to expand ,,trim it off after it dries,,,,except the center of the boat , I left it open for drains.

This is what I will do. I bought a 18 foot Lund Pro V boat that needed a floor and the price I paid for boat motor and trailer was about a 1/4 of what the motor alone is worth, besides I like to do things like this. I am using marine plywood 5/8 thick which will be coated with fiberglass to make it 3/4 inch when finished. The floor is 64 inches wide so I need to join the plywood and there will not be any fancy cutting required. Just one end need an angle cut 6 inches back from the end and 3 inches wide
The old floor is coming out in chuncks as the glue let loose on it so I have a lot of cleanup to do after it is out. I had one of the best days Sat as my 2 youngest grandsons were here and helping. I gave each a drill and let them drill the rivits out of the floor. They worked with me all day and of couse we had to stop for a popcicle every now and then.

[BuckeyeDennis]

What about a floating tenon?

Use a trim router and cut a 1/8" grove down the center of the pieces say 1/4" deep , then glue in one solid long piece of hard wood strip just a little under 1/2"w x 1/8" thick to join them ? " tong and grove" ,,Marine plywood ,,,,I have done this on a old restoration years ago ,,, also fiberglass on both sides and all edges of the flooring will help keep moisture out .

I drilled 3/8 holes in locations and filled the main cavities with expanding foam once the floors were in ,,,, every now and then a few 1/2" holes to allow the foam to expand ,,trim it off after it dries,,,,except the center of the boat , I left it open for drains.

This is what I will do. I bought a 18 foot Lund Pro V boat that needed a floor and the price I paid for boat motor and trailer was about a 1/4 of what the motor alone is worth, besides I like to do things like this. I am using marine plywood 5/8 thick which will be coated with fiberglass to make it 3/4 inch when finished. The floor is 64 inches wide so I need to join the plywood and there will not be any fancy cutting required. Just one end need an angle cut 6 inches back from the end and 3 inches wide
The old floor is coming out in chuncks as the glue let loose on it so I have a lot of cleanup to do after it is out. I had one of the best days Sat as my 2 youngest grandsons were here and helping. I gave each a drill and let them drill the rivits out of the floor. They worked with me all day and of couse we had to stop for a popcicle every now and then.

I like the spline idea, but I'd orient the grain of the spline crossways to the seam, or maybe at a 45 degree angle. Busting a 1/8" thick spline lengthwise along the grain wouldn't take a whole lot of force. Of course, unless you have a mighty wide board to crosscut your splines from, you'd need several of them per plywood edge.