Plywood lamination advice

[space.dandy]

I have three or four 1200x600x18mm sheets of plywood that I would like to glue together to make a thick bench top. The problem is, I don't have anywhere near enough clamps and those that I do have don't have much reach, so there won't be any clamping pressure towards the centre of the sheets.

Is clamping strictly required for mechanical strength, or will the weight of the plywood itself be sufficient? What side-effects am I likely to see if I don't clamp, and will they affect its function as a bench top?

I thought about loading with weights, but I don't have an area large enough that I can guarantee is flat; I'm worried that this method would encourage the plywood to conform to a wonky surface during glueing.

 

[hawkeyefxr]

I doubt the ply would settle down to a good flat surface, if you using it as a bench you will need a flat surface for what ever your making later. As for how you would hold it flat i do not know, you would also need a flat surface for the ply to rest on.
Not much help i know.

 

[Jake]

Cauls are the way of expanding the reach of the cramps you do have, but in your situation I'd just put some screws in to pull the sheets together, building up one layer of ply at a time (well, down really, but working up from the inverted top sheet). Clearance hole in the ply which is being added so they pull the sheets together. Just need to plan and set out your screw positions to avoid any dog hole areas etc and offset a bit from the screws in the previous layer each time so you don't hit the heads.

 

[Yojevol]

You could drive screws in from the underside. They could be removed after the glue is set if you wish.
Brian

 

[AJB Temple]

The sheets are not very big. I would probably do this with a contact adhesive, very evenly spread. Working on the floor a weight like an upturned table will hold everything flat if you are worried about that, but the adhesive should be enough on its own.

 

[space.dandy]

That sounds good. If I do it sheet by sheet, I can use the unglued sheets as flat surfaces and/or weights -- sort of 'Tower of Hanoi' style.

Do you have any recommendations for contact adhesive? I have an aerosol contact adhesive that I've used before for upholstery, but it comes out like a spiderweb or silly string, so I don't think it would be useable for this.

 

[AJB Temple]

I've used evo stik "impact" successfully in recent times. Readily available, inc. on Amazon if you need delivery.

Get a helper to assist you when aligning the sheets as once it grabs, you are done! You can get stuff that allows a bit of slidey around, but I don't find it glues as well. Just align properly in the first place and you are done and can crack straight on with the next sheet.

 

[space.dandy]

Thanks, I was looking at evo stick 'impact' or '528'. Some reviews for 'impact' say that it can be a bit gloopy or lumpy. Have you experienced that?

I was thinking about making some simple corner jigs to help with alignment.

 

[Hornbeam]

I have just been laminating single sided veneered plywood boards together to give a double sided veneered finish. I used Titebond extend which is designed for laminating/veneering. I spread it with a roller and a paint scraper and used a very finely notched adhesive type trowel to ensure an even coating. It gives you a reasonable amount of time and you can move it. A contact adhesive is a one shot. i would have said not as good as a dedicated woodglue (but better fro formica to wood)
The approach of doing it later at a time with woodscrews seems a good one
Ian

 

[AJB Temple]

I have experienced no lump problems.

The reason I like the impact type is that you get it in place and then you can get straight on with the next thing you want to do. No clamping etc.

I would not want hidden screws etc. Too risky if I want to put holes in it later for stops, clamps etc. Not necessary for me to take that risk.

I have glued two 18mm sheets of 2440 by 1200 ply together recently and my wife helped me align them. Wasn't a big deal. For small sheets like this you could do on your own but a helper is handy.

I am not knocking any other method. Just saying what I would do. I did this for the first time when I was a kid, putting formica on a table top I made. Never had a problem with alignment. I find the slop in the adjustable slide stuff a bit annoying and it takes ages to dry. YMMV.

 

[Orraloon]

Wood glue and screws are the easiest way. I have used this method when I built a bench for my lathe. Screw from the underside then remove screws when dry. Contact glue gives you no time to adjust the positioning and unless the whole surface of each sheet is clamped flat then the finished laminate will not be flat. It will have a bulge in the middle. I only did 2 sheets and started the screws from the center of the sheet and worked outwards then clamps at the edges. You would have to do it sheet by sheet for more than 2 layers.
Regards
John