Gluing wide laminated panels on face

Hi there,

Long time lurker, first time poster.

Currently in the process of building a workbench. As I usually do with DIY projects, I've gone way overboard, and the worktop is a bit of a quandry. Because I am new to this, it is my first piece of "furniture", and I am severely tool-limited, I decided to cheat. I purchased two 2400 x 641 x 33 mm "utility-grade" laminated panels in vic ash / tas oak / etc. The intention is to cross-cut each to ~1600mm length and use the ~800mm offcuts to make the middle layer of a 1600 x 641 x 99 sandwich.

My problem is gluing the sandwich together and specifically getting enough clamping pressure in the centre of the 641mm wide boards. I hadn't realised that long reach clamps seem to be rare/unavailable. I'm also concerned that any unseen gaps between layers will cause issues for a PVA bond.

My thought is to do it in two stages (middle layer onto the top layer first, then the bottom layer onto the first two layers). Thus far I thought of two clamping options:

1. A lot of weight (will probably require purchasing several large ~20L water containers and staking them on the centre, with regular clamps around the edges). Problem with this is that I don't think 20kg of weight over 400 ish mm of board equates to that much clamping pressure (especially on stiff hardwood). I also have no use or storage space for the bulky containers after this glue-up.
2. Screwing the gap closed with a load of ~50mm 8G screws. The advantage of this is that I can pre-drill and then use the screws to align the panels. I figure I can also provide a lot more than 20kg equivalent over 400mm, this way (correct me if I'm wrong?). However, given I am making a worktop and I have no idea where i will want dog-holes, the screws will have to come back out again, after each layer is glued.

I'm heavily leaning towards option 2 but keen to see if anyone can identify any problems with working this way. Keen also to hear if PVA or epoxy would be the better option.

Many thanks.

A third option would be slightly convex cauls, so you could just clamp around the edges. However, of the three, I reckon option 2 is probably the best. Either type of glue should work fine. but PVA is a lot cheaper. I'd only use PVA if I thought I was going to run out of time, as epoxy will give you more time.

Concave cauls was my thinking too Alex. Did you mean you'd only not use PVA if you thought you'd run out of time?

Quote:

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Originally Posted by garagegrump

Hi there,

Long time lurker, first time poster.

Currently in the process of building a workbench. As I usually do with DIY projects, I've gone way overboard, and the worktop is a bit of a quandry. Because I am new to this, it is my first piece of "furniture", and I am severely tool-limited, I decided to cheat. I purchased two 2400 x 641 x 33 mm "utility-grade" laminated panels in vic ash / tas oak / etc. The intention is to cross-cut each to ~1600mm length and use the ~800mm offcuts to make the middle layer of a 1600 x 641 x 99 sandwich.

My problem is gluing the sandwich together and specifically getting enough clamping pressure in the centre of the 641mm wide boards. I hadn't realised that long reach clamps seem to be rare/unavailable. I'm also concerned that any unseen gaps between layers will cause issues for a PVA bond.

My thought is to do it in two stages (middle layer onto the top layer first, then the bottom layer onto the first two layers). Thus far I thought of two clamping options:

1. A lot of weight (will probably require purchasing several large ~20L water containers and staking them on the centre, with regular clamps around the edges). Problem with this is that I don't think 20kg of weight over 400 ish mm of board equates to that much clamping pressure (especially on stiff hardwood). I also have no use or storage space for the bulky containers after this glue-up.
2. Screwing the gap closed with a load of ~50mm 8G screws. The advantage of this is that I can pre-drill and then use the screws to align the panels. I figure I can also provide a lot more than 20kg equivalent over 400mm, this way (correct me if I'm wrong?). However, given I am making a worktop and I have no idea where i will want dog-holes, the screws will have to come back out again, after each layer is glued.

I'm heavily leaning towards option 2 but keen to see if anyone can identify any problems with working this way. Keen also to hear if PVA or epoxy would be the better option.

Many thanks.

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I had to this exact same thing (laminate 3 layers of utility-grade panels) when I built my SCMS hybrid bench/station. As suggested by others, I used cauls. Where my method differs was my cauls were flat (not concave or convex) and I used 10mm wide hardwood strips of varying thickness between the top caul and the material anywhere I wanted to apply pressure along the width of the panel (i.e. in the middle). This way I could dictate how much clamping pressure I applied in the middle of the panel by varying the thickness of the hardwood strip. My sweetspot was about a 3~4mm thick strip. If you need more pressure, you can go 7mm. This will depend on your caul's ridgity determined by it's thickness, width and what it's made of. I was using blackbutt with cross sectional dimension of 60mm x 40mm And the other advantage is you can change where pressure is applied by changing the position of the hardwood strip.

I hope that all makes sense and good luck with your workbench build. I'm about to start on mine as well.


Cheers,
Mike

I made my bench in a similar way, but with only two layers of laminated panels. The Piggy Bank Workbench I used screws to clamp them together while the glue dried, worked fine. Just remember to tighten the screws from the centre of the benchtop, working your way out.

I would also go the screw method. As you have said predrilling will also sort the alignment. If the screws go in the bottom then the holes will not be noticed. Do 2 layers first time and remove screws when glue is dry then repeat. I have screwed up layers of particle board this way for my lathe bench. As woolybugger said tighten up the center first and work out. I guess you could even use clamps round the edges as the whole point of screws is to get pressure in the middle where the clamps dont reach.
Regards
John

Thanks all for your advice. Much appreciated.

I'll probably go with screws, but the cauls-with-packers method is very intriguing
As to adhesive I'm leaning toward epoxy now that I have laid the panel parts together dry. I have also already gone and epoxied a few checks, knots etc, and PVA will probably not bond to this.:doh:

Thanks again

If you're in SA you're welcome to bring them over and we can press them in my vacuum press. Even clamping pressure. I'd suggest Techniglue epoxy. Look up vacuum bag veneering and just imagine that each piece of your benchtop is a 'veneer' so you're just making a giant version of plywood pretty much.

Quote:

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Originally Posted by hurcorh

If you're in SA you're welcome to bring them over and we can press them in my vacuum press. Even clamping pressure. I'd suggest Techniglue epoxy. Look up vacuum bag veneering and just imagine that each piece of your benchtop is a 'veneer' so you're just making a giant version of plywood pretty much.

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Very generous offer!

Thanks but I am in Perth so not really doable.

I got there in the end. Went with option 2 as mentioned and used West Systems Epoxy and microfibre filler. First layer glue up, i used a boatload of 8G screws. This did not go perfectly as I pre-drilled too large. Couldn't get quite enough clamping and ended up with a few gaps at the edges (not quite fingernail thickness). However, the screws came out afterwards nicely.

Second layer I went with 10G screws and tighter pre-drill it came together really well. Decent amount of squeeze-out. However three screw heads twisted off completely when removing them. I used some car spray wax as a kind of release for the screws, but clearly this didn't work in all cases.

In each layer I filled the empty screw holes up with more epoxy.

Incidently a 1600 x 641mm panel is damn near 1 square metre, and I managed to hit upon an approximate coverage for estimation:

150g (125g resin, 25g hardener) for pre-coating each side (300g total).
600g (500g resin, 100g hardener) plus filler for the "glue" layer. Depending on how neat the joint is this could probably be reduced. My second glue up was much better and about 100g must've squeezed out.

So after 2 utility bench tops and about 2kg of epoxy I now have a solid 100mm thick workbench top.

Thanks all for your advice.