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Crude Adhesive test

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newt

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I had a requirement to extend a length of 18mm MDF by butt jointing and glueing with biscuits. However before this I thought I would see how butt jointed MDF would perform with out biscuits.

I cut 4 250mm by 250mm samples cut each in half on the table saw and then glued them back up. Before gluing I noticed on the cut edge when checking with an engineers square that the centre core of the MDF was slightly raised making the edge slightly convex, one pass with the plane gave a perfect edge. I first tried 3 PVA based glues: WUDCARE 5 minute super fast PVA, EVOSTICK W and TITEBOND 3. I brushed on a a fairly thick layer on each mating edge and clamped, waited 24 hrs and carried out a crude strength test, I placed one half of each sample in a vice with the join just level with the top of the vice. I suspended a 2 pound (old money) hammer on a cord attached to the roof above, and set it so the face of the hammer was in the centre of the top half of the panel.

I pulled the hammer back in an arc to 600mm from the test piece and let go, and not surprisingly all 3 samples failed at the clue joint. I then reapplied the same glue back on each of the joints and repeated, I could not fail the joint even when I smashed with the same hammer using both hands, the MDF finally failed randomly but not on the glue joint. Perhaps this is not a surprise as the edge of MDF is very adsorbent and I guess the first application just primed the surface.

However there was a further positive surprise, I repeated the test but this time with SOUDAL pro + Polyurethane rapid adhesive, I could not fail the joint with just one application of the adhesive.

So my very crude test results when subjected to a heavy instantaneous bending load, the 3 PVA glues failed with one application, but a further application provided a stronger joint than the MDF, however the Poly gave the same joint strength with just one application. It should be noted that a sustained bending force or continuos tension test may yield different results.
 

PowerTool

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Hmm - interesting :-k

Thanks for taking the time to test it and post the results - have you compared MDF joined with biscuits yet ?

Andrew
 
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Anonymous

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I switched to poly glue this winter as the pva was taking to long to go off, with the intension of switching back to pva in spring.

Never bothered to switch back, dries very quickly, cleans up really good once you get use to it and as you say joints are so strong. I used to buscuit all my door panels very time consuming, with this glue i just butt them.
 

Evergreen

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Newt

Veeery interesting. I've suspected for some time that the latest generation of glues get pretty close to making traditional woodworking joints obsolete. I'm not familiar with the poly glue you used - is it readily available, please?

Regards.
 

newt

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The poly glue is available from my local merchants in Salisbury it is made by a Belgium company

Soudal N V Everdongenlaan 18-20 B-2300 Turnhout Belgium Tel + 32-(0)14-42-42.31. www.soudal.com.

I would always use biscuits mainly for alignment but they would also add some additional strength in bending I suspect.

By the way this poly glue is also useful for bonding non wood products eg I had some crazy paving that had broken and some external sill tiles that had come loose from the mortar, worked perfectly they have not moved in 2 years. There are only a couple of down sides, 1 if you get it on your hands and you do not wipe if off within a couple of minutes with acetone it will be with you for a week, 2 if you cannot clamp the joint you will need to hold it in place for ten minutes until it stops foaming. I suspect any of the Polys will work, another brand is gorilla but I have not tested.
 

Paul Chapman

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I always use biscuits when gluing up MDF, but the other day I was gluing together two pieces of 18mm MDF to make a piece 36mm thick. As I was going to cut it to size after gluing, I didn't bother with the biscuits, but as I tightened the clamps the two pieces slid about all over the place - I think I will revert to always using biscuits in future.

I'll be interested to hear the results of any similar tests you do with biscuits, newt. Whenever I've done similar tests, I've always found biscuit joints very strong and the material has always broken somewhere other than the joint - which is why I am rather surprised that in some publications some writers tend to imply that biscuits do not add much strength. In my experience they add considerable strength and, given the speed and accuracy of biscuit jointing, it's my preferred method for jointing man-made boards :wink:

Paul
 

Jarviser

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I am of the same opinion, and will always leave the PVA to soak in for a minute or two on MDF, then apply another thin layer before putting the pieces together. If the thin glue layer in the joint continues to soak in after assembly, it has no option but to draw air into the joint (IMHO). I would not like the glue to start curing however, so only a minute or two is needed.
I had a similar discussion on this topic here about mdf and Extramite , which advises to apply to one surface only - I now disregard this advice when using mdf and work the extramite well into the surface on both pieces, because it just soaks it in.
I don't wet the biscuits until the second application with PVA or Extramite.
 

9fingers

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Newt,
Which supplier do you use in Salisbury please? I'm not too far away in Romsey and good do with a good local dealer for wood related things.
I'm getting pretty fed up with the sheds near to me.

regards

Bob
 

Pecker

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express construction was selling soudal extremly cheap I bought 24 tubes for about £3.70inc vat each. I recently ran out but replaced it with Lumberjack by Evode and personally both I and my colleague prefer it - however the Ssoudal (Purcell?) is still a good glue. I now very rarely use PVA at all.

As a side issue "Sticks like ****" made by evostik is a really weird glue originally made for replacing engine gaskets. It sticks plastics and wood very well but gives elasticty to the joint, yet is virtually unbreakable.

Which begs the question.. who still uses Uhu? (or good old Cascamite?) LOL
Mark
 

newt

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9fingers, sorry for the delay in responding

The suppliers are: Salisbury joinery & timber Co, 14 Edison rd Churchfields Ind Est, Phone 01722 337040. They are an old firm and they ban swearing and the use of mobile phones.
 

Pecker

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Newt, from memory aren't they Plymouth Brethren? I'm sure they're inter-related (possibly literally!) with several more Brethren fixings outlets. they believe the mobile phone, computers and bits are "evil". basically they are purists which is why swearing is also banned and all women are submissive and wear headscarfs. I used to call on them as a rep.

Mark
 

9fingers

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Thanks Newt,

I'll have to drop in next time I'm that way. I don't carry a mobile phone so I should be OK. The submissive women could be interesting however!!

Bob
 

Tony Spear

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Just a question about the PU glues (and for that matter all the glues that use those stupid long nozzles that you cut off to size) - how thehell do you stop the stuff going off in the nozzle if you don't use it for a few days?

With PVA I just unscrew the nozzle and run hot water through it so that it's clear before I put the thing away, but I can't imagine standing there pouring Acetone through a 4" long nozzle!
 

Pecker

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Tony, Most PU glue comes with little caps for the end of the tube. if not, then clingfilm works well, or a 3" nail down the tube from the top. If it goes off, then unscrew the tube get a 4" screw, screw it in and pull! (I always have to do that with silicon:-( )
Mark
 
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