What adhesive - that shrinks when it sets - do you recommend for melamine laminate sheets?

Yes I suppose they have all that stuff available that cabinet makers etc must use when doing kitchen cabinets etc with Melamine. Just a matter of prowling the local hardware store or home reno shop.

Yep, the idea of having the boards double sided to help stop bowing is good. taking facing off the two surfaces to bond to each other solves that, still faced on outer sides after bonding. Problem is, however you do it, without a laminate press you can't ensure, at that size they will be flat parallel faces. Unfaced 32mm MDF is available so you could face both sides with laminate using 'Cascomite' (Ahh remember it well for making toy boats) but when mixed, add a few drops of Meths to disperse air bubbles in mix.

Regards Ian.

Thank you for all your thoughts.

Frances - no, for a number of reasons I intend to use both sides.

Yes, I am working on a folded table, but it HAS to be a folded table. [For the love of God, please don't anyone else suggest buying a whole new table - KISS!!]

Hopper - And no, as I have already said, I will not JUST be using it under a cutting mat. Please stop over-thinking your answer and just attempt to answer the question. If you have nothing of value to add please then please don't!

Raymond - To state the obvious, the more sheets that are bonded together the less likely they will be to warp after they have been bonded together. But if & when it does warp after I have bonded the 2 sheets together, I shall cross that bridge.
But IF gluing fails then screws, pref from one side only & filling them carefully could be done. But I would much rather have a complete, sound melamine surface if I can. Also unless I put a screw in the middle of my sheets (thereby screwing up a perfectly good nice, flat, easily cleaned melamine surface) it will be more likely to warp with screws than with adhesive.

In truth the only reason that I have not yet implemented gluing option is that my MDF sheets are in use underneath ongoing projects!

I have yet to check whether there is any slight pre-existing warping in my MDF sheets when removed from the table, buy if so, then I shall of course arrange them back to back so as to cancel each other out as much as possible.

Don

A very simple, low cost solution to a wobbly folding table that you cannot replace is to work on the floor.

Making an 1 1/2” thick piece is unlikely to fix your problem.
3/4” is already quite heavy and very stiff.

By doubling up you double the weight but the stiffness will only go from very stiff to really very stiff…

If 3/4” is not stiff enough then you really have to question the supports or the force you are putting in.

Doubling the weight on a suspect support is dubious from what little information you have supplied.

Dave

Well far be it from me to disagree with you Don but I think you will find that if two flat surfaces (as you describe) are screwed together there is far less likely hood of them warping than if bonding for the simple reason that each layer has the ability to stretch/shrink without directly influencing each other but as said 'yer pays yer money' etc..

If you want to potentially waste two (or more ?) sheets of faced MDF in order to find out by all means do so. Something tells me however that had you screwed them together from one side only you would be well into being able to use it by now - one side nice and clean with an un-interrupted surface to use as such, the other 'unclean' side to be used under the cutting mats.

Whatever I think you must have garnered enough information and help from the replies to your call for help on here to enable you to make a firm decision by now - good luck with it how ever you do it

Ramon - No Y No D BTW - and usually referred to as Tug 

Edited By Ramon Wilson on 01/04/2022 16:53:32

When formica was all the rage we used a glue called Thixotropic made by evo-stik.

To my mind Donald's post just after midnight yesterday changed the question completely.

If I read his second post correctly, the question is how to improve the rigidity of a table-top, not 'Which shrinking glue is best for sticking sheets of MDF together (without warping)?'

Warping is not the same as sagging. Warping occurs when two sheets expand at different rates due to heat or humidity. A good way of stopping it is to let the sheets slide: this is why bridges have expansion joints.

Sagging is when a girder (or table top) deflects due to it's own weight, and a load. Benches and kitchen worktops are kept flat by having multiple supports underneath, and although a comprehensive frame can't be built-in to a folding table, putting temporary props underneath might be a satisfactory solution.

Sag is reduced in proportion to the depth of the girder, so another way of approaching this is to glue deep narrow ribs between the two sheets. Ribs increase the effective depth of the table-top, reducing sag, and the extra depth is obtained without adding much weight. Welding two strips in a 'T' is much more rigid than welding them into a single flat:

Wood might do, otherwise deep Aluminium I-beams. Another observation, in a ribbed sandwich the lower sheet can be thinner than the top sheet, or even wires. This is because the top sheet is in compression and has to resist buckling, unlike the lower sheet which is in tension.

In engineering it's usually best to start with the actual requirement. Otherwise everyone ends up wasting time producing complicated solutions to the wrong problem that don't work very well! Apologies if I've misunderstood, but it appears this requirement is more about designing a bridge than choosing glue.

Dave

Perhaps you should try stating your problem clearly in the first place instead of -- once again -- drip feeding often contradictory information as members spend their time coming up with solutions for your partially described problems that never seem to be up to your exacting standards

You can't hope to do precision -- certainly not to the standard you aspire to -- work on a folding table. A length of 4" x 2" timber wall studding cut up and screwed together will make a stout table frame an four legs for your MDF boards and cost about the same as one or maybe two cups of skinny soy latte coffee. Could be made with hinged legs for folding up. Or hinged off the wall with two outrigger legs. A bit of lateral thinking should solve most of your problems.

And being rude to those spending their time trying to help you is probably not the way forward, either on the forum or in life.

Edited By Hopper on 01/04/2022 22:28:18

If I was in the unfortunate position of needing to produce a metre square, flat and negligibly deflecting under its own weight, cutting board: I would start by looking at honeycomb and/or foam cores.

But I did work in a vibration test facility, so I may possibly have a head’s start, Donald.

MichaelG.

Hopper, Hear! Hear! well said!

Robert Butler

+1 for ^^^^^

Rob

C'mon guys, don't you like to rise to a challenge? Took more than 20 replies to find out the thickness (sic) of the material we were trying to bond. Dentistry springs to mind.

Regards Ian.

To be fair my original question was simply:
"What adhesive that shrinks as it sets would you recommend to bond two large sheets of melamine covered boards (AKA laminate) together?"

There was me thinking that this would be nice simple question!

Well it turns out that I nobody is aware of any shrinking glues for melamine... other than wood glue, which I think we can agree  would probably never set.  Ok fine, I'll just have to abandon the shrinking requirement. 

But mysteriously I find myself sucked into a detailed analysis of my workshop... my project, why do I need such precision, why can't I use screws not glues, is really melamine, why melamine, my approach, my lifestyle, and if I ignore anyone's suggestion then offense is taken.

Any then it's why didn't you tell us about: your workshop, your project, your need for precision, why you don't want screws, whether it really is melamine, why you want melamine, what kind of table you have, why you bought that particular table, why you live where you do... etc etc at the start?

I mean I'm grateful for all the suggestions... but where will this process stop? Will it be the name of my cat and my inside leg measurements next?

Don

Edited By Donald MacDonald 1 on 03/04/2022 13:01:21

.

As you haven't acknowledged my previous post, I will try again:

Use the thinnest sheets of Melamine Faced MDF that you can get, and use them to sandwich a suitable core material.

Do some Google-based research and you may get to understand why this is a good idea.

MichaelG.

Apologies, Michael. Yes, that sounds like a good idea. Maybe a layer of plywood or MDF that would absorb the solvent/water and thereby form a bond.

In fact maybe I could use shrinking wood glue after all

Given how large & heavy the MDF melamine sheets are (which like I say, are 18mm thick and which I have already bought, btw), who thick do you think the MDF/plywood sandwiching layer would have to be at a minimum as it is already fairly heavy....

Don

Edited By Donald MacDonald 1 on 03/04/2022 13:08:33

Not mysterious at all! Have a think about how your 'nice simple' question is interpreted by an experienced engineer.

"What adhesive that shrinks as it sets would you recommend to bond two large sheets of melamine covered boards (AKA laminate) together?"

The question screams 'wrong approach' for practical and theoretical reasons. Unusual for anyone to want to glue melamine laminate boards together, and unusual in this context to need a glue that shrinks as it sets. Although there might be a legitimate reason, it's unlikely. The question starts off key and a strong suspicion important detail is missing.

And so it proves. Later, we're told 'I am wanting to create a rigid work surface that is as flat as possible.' which can't be achieved by gluing two sheets of Melamine together, whether the glue shrinks or not. The underlying way it's imagined the solution will solve the 'rigid work surface' requirement is badly flawed. (Michael's ribs are a much better bet, conventional engineering, and not difficult to make.)

Confusions and red-herrings are best avoided by starting with the Requirement, because it avoids getting deep into a design only to discover it's an expensive way of producing a bad solution. (Happens a lot in engineering!)

No-one cares about inside leg measurements and lifestyle, but it's important to members on the receiving end that questions communicate clearly what the questioner is trying to achieve, ideally without hidden pre-conceptions and definitely not with important details sprung as surprises later.

Don't be disheartened - design is the hardest part of engineering. We're only trying to help, and questioners tuning into what answerers need to know makes it much easier to do a good job.

Dave

Edited By SillyOldDuffer on 03/04/2022 14:01:42

Don what is wrong with telling us a bit about what you are doing, if you really don’t want to tell us anything about what you are doing maybe you shouldn’t ask for our help, after all is what you are doing such a secret, anyone would think you are doing work that you intend patenting.

As an off-topic;ish thought does the glue really matter? If one placed the two boards together with any gap-filler (say water) and applied an air-tight edging then air pressure/vacuum would hold those boards together? Indeed, the thinnest layer of any thin bonding agent that can occupy any gaps would be the best?
I'm minded of the time I built some fitted wardrobes into an old house with lathe and horsehair plaster walls with a tendency to crumble. I glued a 12 foot length of 1/2 in baton to the wall with PVA and held with a few of pins until it set and was able to suspend my 110kg by the fingertips from it just by the sheer area.

pgk

.

Please read my earlier post more carefully

I suggested using foam or honeycomb as the filling for the sandwich ... Originally they used endgrain Balsa Wood ... it only needs to be stiff in compression.

MichaelG.

Forget about the glue, why not use magnets to hold the two sheets together you can get Neodymium magnets in all shapes and sizes suitable for recessing into the joint face of your boards and give a firm joint.

MichaelR