Which glue to join two 17mm ply sheets to make one 36mm thick.

Stephen B

Stephen B

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May 6, 2013
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[size=14pt]
I wish to join two 17mm thick ply sheets to make one 34mm for a bench top in the Untidy Shop. My immediate thought is using contact adhesive, coat both contact  surfaces, wait 20 mins join and clamp, or should I use the wet method of coat one surface and immediately join and clamp?

Or are there other alternatives in glue/techniques?

With thanks.

[size=10pt]Edit I know I could just purchase thicker ply, but I have plenty of 17mm as they are heavily discounted where I work PTime.
 
I would use plastic resin glue.  It comes in powder form and you mix it up. It makes a hard glue line which helps stabilize laminates.  It can be clamped with weights in the middle, or screws of course.  In N. America there is this stuff called Liquid Nails which comes in a caulking tube.  I think it is some sort of plastic resin glue. 

I would not put my trust in contact cement in this sort of application.  It really works best when one or both surfaces are somewhat flexible and able to conform to the other surface.
 
White glue on both faces and stick them in a vacuum press would be my method.
 
Cascamite.  It's easily spread, waterproof, suitable for structural joints and most importantly has a long open time.

Andrew
 
Hey Untidy Shop -

You might want to edit your subject. Your first post says "join two 17mm ply sheets to make one 34mm thick", but the subject says "to make one 36mm thick".

Unless you get some glue that REALLY swells up the plywood, I'm pretty sure that 17mm + 17mm is gonna = 34mm?

[poke]  [big grin]

Then again, you should always check my math because I *AM* known to be 'Metric Challenged'.

[embarassed]

 
In your application, the type of glue may be superfluous.  That said, something in the back of my head says no contact center; but that could just be last night’s dinner talking.  [embarassed]

Since all you’re doing is bonding two horizontally flat surfaces, PVA glue (for example, Titebond) will more than meet the requirements.  Even if you were to use the resultant glue-up in a vertical application, in other words, the glue would fight a shearing action, the bond between the plies or the plies themselves would probably give before PVA glue would.  There are probably more PVA bonded workbench tops around than anything else.

Just spread a liberal amount across the first surface (brushed clean of course...), screed it smooth and cover the entire sheet, place your second sheet on top, then clamp.  When clamping make sure you have sufficient pressure across the entire surface while the glue sets up.  Cauls would be good in this application.  When I last glued something like this, I did not have cauls handy, so I/we placed about 5 or 6 50lb sacks of sand in the middle and clamps around the perimeter and a few on end 2x4’s across the middle.  The end result was perfect.

I think your only decision between types of PVA glue would be open time and water/moisture resistance.
 
you're going to be glueing long grain to long grain.  childrens white glue will be stronger than the wood once set.  pretty much any long open time glue giving you the time you need to get it all clamped together will be fine.  i think someone mentioned vacuum pressing.  That would be the ultimate clamping method here.  If you have a bag that big [huh]
 
[size=14pt]

Thank you all for your replys so far. More thoughts/ideas welcome.

WOW - a long day, guilty as charged!  [big grin]
 
For the cauls, if you put a slight radius on them, when you clamp the ends it will maintain pressure in the middle as well.
 
G'day Untidy Shop, Given that you are in Australia, I would use Selleys Aquadhere Exterior, which according to the glue bottle is "an industrial-grade polyaliphatic cross linking PVA especially developed for use by professional Woodworkers and Craftsmen. It produces bonds stronger than most woods and is ideal for softwoods, hardwoods, particleboard, chipboard, plywood and MDF." "...it is excellent for laminating...."  I have never had a joint fail using it. The exterior grade is weather resistant.
 
Aquila said:
G'day Untidy Shop, Given that you are in Australia, I would use Selleys Aquadhere Exterior, which according to the glue bottle is "an industrial-grade polyaliphatic cross linking PVA especially developed for use by professional Woodworkers and Craftsmen. It produces bonds stronger than most woods and is ideal for softwoods, hardwoods, particleboard, chipboard, plywood and MDF." "...it is excellent for laminating...."  I have never had a joint fail using it. The exterior grade is weather resistant.
Click to expand...
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Given the thoughts of others here re PVA, I will probably follow Aquila's advice as I know and often use this Selleys PVA he suggests.

Will display result here in 1-2 weeks, as I have more urgent tasks this week on the Owner Build.  [eek]

Thanks again to all who responded.

 
Thank you Mike I have bookmarked that article you shared.  I knew I saw it somewhere, but could not recall.
 
Assuming the kind of wood you are using is not somehow resistant to glue, it really doesn't matter much.  As others have pointed out, modern glues are generally stronger than the wood once they set.

Use whatever kind of semi-modern wood glue (titebond, gorilla glue, "white" glue, etc.) is on hand.
 
[size=14pt]
Finally had an opportunity today [Sunday, AESST] to glue up the two sheets of 17mm non-structural ply. Due to another project and my requirements for this top, their size is now approx. 2400X900mm.

Used Selley's Aquadhere Exterior glue as suggested by Aquila and 90X45mm dressed Mountain Ash as pressure rails and 'Gauls', both above and below the two ply sheets. Glue spread by fencing brush.

Thank you all for your suggestions.  [smile]

[attachimg=1][attachimg=2]

What happens next will feature ASAP on the thread - 
http://festoolownersgroup.com/workshops-and-mobile-vehicle-based-shops/the-tidying-of-the-untidy-shop-project-1/msg323579/#msg323579
 

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