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  • Need help attaching two pieces of plywood.

    Hey guys,

    I'm looking to attach two pieces of plywood (¾ x 4x 8) together. While I do plan on using wood glue to reinforce the connection, I need to figure out a more stable & secure primary method of securing them (like nails or screws), but the question is : How do I accomplish this? The two pieces of plywood will be flat on the ground, and I want it to be one big piece (to make a portable floor).

    Can anybody advise how I can do this?
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  • #2

    Re: Need help attaching two pieces of plywood.

    This is one application where biscuits shine. Place them about every 4" & be sure to get plenty of glue in the slots and on the biscuits. But it still will need very careful handling to avoid breaking the joint. I suggest you use 4 sheets of 3/8"; 2 on the bottom and 2 on top, with the with them glued up 90* to each other.
    Darrell likes this.

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    • #3

      Re: Need help attaching two pieces of plywood.

      Originally posted by drzaius View Post
      This is one application where biscuits shine. Place them about every 4" & be sure to get plenty of glue in the slots and on the biscuits. But it still will need very careful handling to avoid breaking the joint. I suggest you use 4 sheets of 3/8"; 2 on the bottom and 2 on top, with the with them glued up 90* to each other.
      I just watched a video on these biscuits (if indeed it's the same thing you've mentioned) : https://www.youtube.com/watch?v=ZNd7I4OiOf8
      The problem is I don't feel comfortable with that type of a solution, because as you wrote : "But it still will need very carefully handling to avoid breaking the joint."
      I need something more solid/stable.

      I've been doing some research & I came across this product : https://www.lowes.ca/product/angles-...rap-tie-401982
      Unless I'm mistaken, this is sort of like a joining bracket, so I should be able to place this plate (strap tie) overlapping the two pieces of plywood, apply the wood glue on both joining pieces of plywood, and screw in the plate (strap tie).

      Am I correct?

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      • #4

        Re: Need help attaching two pieces of plywood.

        That sounds just fine if you want it to look agricultural, how about a strip of 12mm ply on both sides about 150mm wide.
        The suggestion above for 3/8 ply laid opposed sounds good but you need a big vacuum table so you get even pressure all over when you glue them together otherwise you will have voids in the glue up.
        The best way would be a scarf joint (google it) its a method we used when building boats and we needed big sheets, its a joint that needs a lot of attention to detail being along the 8 foot side of a sheet, done correctly it would be strong and if painted hard to see.

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        • #5

          Re: Need help attaching two pieces of plywood.

          I would skip the two 3/4" ply and use four 3/8" sheets


          lay 2 down side by side, small biscuits may work here. or you could use a router to cut a slot the full length of each sheet, and rip a thin spline to glue in place betweem them for added strength.

          then lay 1 sheet down in middle of the 2 others and apply plenty of wood glue between them, using wood screws in a grid every 1' or so

          with the remaining 1 sheet, cut it in half and lay those on either side of the full sheet. glue & screw it down same as other

          once done flip it over and you would have one clean side with only 1 joint and no screws visible (providing you don't sink any too far to poke through)
          Last edited by beakie; 11-07-2019, 03:10 PM.
          Redneck Albertan and schor like this.
          [insert something witty here]

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          • #6

            Re: Need help attaching two pieces of plywood.

            I think Frank has the solution, four sheets of 3/8" plywood, two running opposite to the other two. You say it will be on the ground,So you should use pressure treated and PL Premium or Titebond 3 glue. Maybe explain a little more what the purpose is. Assume you don't have a vacuum press so you need a lot of weights spread around to bond the two sheets, better option would be to use 1/2" screws in a fairly tight pattern to pull the sheets together. If appearance is a concern they can be on the underside. Probably should be stainless or galvanized but once the glue has set they have done their job and you could remove them so they don't corrode. Don't think a butt joint even with biscuits would survive much torture like walking on it especially if the ground underneath is not perfectly flat. Well made scarf joint would probably work but takes more skill than the 4 sheet idea.
            Darrell likes this.

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            • #7

              Re: Need help attaching two pieces of plywood.

              Buy an 1.5" thick sht.

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              • #8

                Re: Need help attaching two pieces of plywood.

                Originally posted by Bill R. View Post
                Buy an 1.5" thick sht.
                Why?? He's trying to end up with a 3/4" by 8' x8' sheet.

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                • #9

                  Re: Need help attaching two pieces of plywood.

                  Finger joint and some short slots ?? at right angle to the joint. The proper terminology escapes me for the slots.
                  Egon
                  from
                  The South Shore, Nova Scotia

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                  • #10

                    Re: Need help attaching two pieces of plywood.

                    I think the term you are thinking of are splines but I don't think it would be practical to try finger jointing two 8 ft plywood panels together.

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                    • #11

                      Re: Need help attaching two pieces of plywood.

                      Overlapped 3/8" like Tom said would be my goto. I would glue it and screw it into 2x4's or whatever for clamping pressure. Pull the screws and fill if you care about the holes. They will eventually just close up anyways.
                      Steve The Drill Sergeant
                      Check out MyShopNotes on YouTube.

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                      • #12

                        Re: Need help attaching two pieces of plywood.

                        You mention "portable" 8x8 of 3/4 doesn't sound too portable.

                        Have you thought of a connection using hardware that you can take apart for transport?

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                        • #13

                          Re: Need help attaching two pieces of plywood.

                          Originally posted by Doug G View Post
                          I think the term you are thinking of are splines but I don't think it would be practical to try finger jointing two 8 ft plywood panels together.
                          Not splines. Pieces of wood inlaid at right angles to the joint.

                          What’s impractical with finger joints. They see lots of use in commercial products with being assembled on automated assembly lines.

                          Egon
                          from
                          The South Shore, Nova Scotia

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                          • #14

                            Re: Need help attaching two pieces of plywood.

                            What is the actual use case? It sounds to me like just using a few hinges on the bottom side would both hold them together in use and allow them to be portable.

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                            • #15

                              Re: Need help attaching two pieces of plywood.

                              Interesting question. Without knowing the exact application, my first thought is that Franks suggestion to use four pieces of 3/8 plywood over lapped perpendicular to each other would be the strongest option. Getting that clamp good and flat all over would be difficult though. Another option would be simply to go buy some tongue and groove three-quarter inch floor sheeting. This is sheets of three-quarter inch plywood that comes with tongue and groove joints already machine into the long edges. We use it for sub floors in houses. Fill the groove of the one sheet with glue then use a couple pipe clamps to suck them together.

                              As others have wondered though I also wonder about the port ability of an 8x8 surface. Knock down Hardware or I suggested above a pair of hinges might make this more portable.

                              What is the floor used for though? On what kind of surface will it be sitting? If it is going to sit outside for example I'm not sure just plywood laying on the ground would give you a very stable floor at all.

                              Depending on what you are going to use it for I might make up a simple 8x8 frame from either 2x2 strapping or 2x3s, frame it up just like you would a wall on 16 inch centers, then glue and screw your two sheets of plywood directly on to it.

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