FWW article on strength of Glues

[Howard Acheson]

Now that I have had a chance to read the article in FWW, I think the test is basically flawed. Unless I'm missing something, no clamping pressure was applied to the joints. With the exception of epoxy and hot hide glue, all of the tested adhesives require clamping pressure to ensure full adhesive strength.

While I am not a fan of Poly Glue, it does require strong and long clamping to develope full strength. As I recall, the instructions call for 200 psi of clamping pressure for 12 hours. The reason that clamping pressure is important with Poly Glue is that large pressures forcing the joint apart result from the expansion characteristic of the curing adhesive. If tight clamping is not used, the surfaces will be forced apart and the joint will be filled with a foam rather than the adhesive. The foam has very little strength and may explain the poor adhesion results for that product.

There are a number of standard tests for adhesive strengths. I wonder if the writer researched any of those sources. Also, I wonder if he solicited any comments from the manufacturers.

I am sending a letter off the the publisher of FWW and may raise the issue on their website.

When it's all said and done, their results may be relevent but the fact that all had at least some wood failure shows that all had strength greater than the strength of the wood itself.

[CPeter James]

I am with Per on this. The Pl Premium is not for everyting, but it does hold and will fill a void. It is NOT for fine furniture, but for the "how do I gue this job" it may fill the bill. I buy it by the case and I am not a contractor.

CPeter

http://www.stickwithpl.com/Products....ction-Adhesive

It will stick just about anyting to just about anyting.

[Mike Henderson]

Now that I have had a chance to read the article in FWW, I think the test is basically flawed. Unless I'm missing something, no clamping pressure was applied to the joints. With the exception of epoxy and hot hide glue, all of the tested adhesives require clamping pressure to ensure full adhesive strength.

While I am not a fan of Poly Glue, it does require strong and long clamping to develope full strength. As I recall, the instructions call for 200 psi of clamping pressure for 12 hours. The reason that clamping pressure is important with Poly Glue is that large pressures forcing the joint apart result from the expansion characteristic of the curing adhesive. If tight clamping is not used, the surfaces will be forced apart and the joint will be filled with a foam rather than the adhesive. The foam has very little strength and may explain the poor adhesion results for that product.

There are a number of standard tests for adhesive strengths. I wonder if the writer researched any of those sources. Also, I wonder if he solicited any comments from the manufacturers.

I am sending a letter off the the publisher of FWW and may raise the issue on their website.

When it's all said and done, their results may be relevent but the fact that all had at least some wood failure shows that all had strength greater than the strength of the wood itself.

I think their test was supposed to test the strength of a M&T joint where you can't clamp the wood beyond holding it into the mortise. The reason they used a bridle joint is so that when they did the actual test, the only thing holding the tenon would be the glue - no strength from the wood on the side of the mortise.

Your point about the wood failing is right on - for any test where the wood failed, the glue was more than adequate. But the wood didn't fail on all joints and glues tested - only on some of them.

Given their objective, I think the test was fair. We just have to realize that the test only applies to M&T joints.

Mike

[Mike Cutler]

End grain glue up in 2 stages: first stage: seal the end grain with epoxy. Second stage: sand and re-apply epoxy and make the glue joint.

Any one ever tried that?

According to the boat guys,and the epoxy forums. That techinique is similar to "sizing".
The epoxy can be drawn via capillary action up into the wood with heat applied. The ends are the "sized" and a susequent application of epoxy is applied.
I've done it on limited application where I wanted the ends completely sealed.

Bob Smalser wrote about it once. I think on this forum.

[Rick de Roque]

What I don't understand is if the wood fails and not the glue than how can they say there is a differance in glue strength (This is only for the glues that didn't fail but the wood did). once the wood fails then its a test of the wood strength not glue strength. They said some glues held better than others but its was the wood that failed, so it was a test on the wood. I'm missing something? Again this comment is only for the glues that tested stronger than the surounding wood.

rick

[Chris Friesen]

What I don't understand is if the wood fails and not the glue than how can they say there is a differance in glue strength?

Maybe some of the glues only bonded in places where there was near-perfect wood/wood contact, while others had more gap-filling ability and bonded more of the wood together?

In both cases the wood might fail, but there would be *more* wood to fail in the second case, thus leading to higher strength.

[Dan Racette]

I was really bummed that plastic resin glue didn't even make the list. I was hoping to get that in the comparison. I am a big fan of URAC 185, and was also impressed by Bob's discussions about repairability. I like Plain white PVA glue, though, as it does dry clear.

Anyone else perplexed by such a fine publication leaving that absent from the testing?

Dan

[Steve Sawyer]

I've used Gorilla glue for bonding non-porous stuff like aluminum and plastic. Normally I would never go near a piece of wood with that crap, but I did find one application that is working out so far.

I had some thin 1/4" lignum vitae planks that I wanted to bond to the bottom of a padauk plane blank (I was making a Krenov-style fore plane). Given the oily nature of lignum, and the fact that the PU glue is a little less brittle than PVA glue, I cleaned both surfaces w/acetone, applied a very thin coat of Gorilla glue and clamped the hell out of it.

I've been using this plane on a regular basis for several months, and so far, so good.

[Curt Harms]

My last two attempts at Gorilla Glue have messed up the project. One I finally planed down to clean wood. The other, gluing aluminum to oak, I messed up the aluminum finish and the glue still isn't off.

What (besides a gorilla) shoul I use for joining unlike materials like wood and aluminum? Epoxy?

Hi Brian-

I've used Roo Glue purchased from WoodCraft to glue aluminum T track in plywood dadoes for jigs. No screws or metal fasteners and so far nothing has come loose. No mess like Polyurethane, no mixing like Epoxy. It's like PVA but will glue melamine, metal and stone. I just looked on Woodcraft's site and didn't see Roo Glue so perhaps only the local stores carry it.

HTH

Curt

[Grant Wilkinson]

I've not seen the article yet, but can someone tell me what glue would be best to glue pressure treated 2x4 to a fibreglass boat deck? I was about to use Gorilla, but you guys have me worried now.

[Jules Dominguez]

I was really bummed that plastic resin glue didn't even make the list. I was hoping to get that in the comparison. I am a big fan of URAC 185, and was also impressed by Bob's discussions about repairability. I like Plain white PVA glue, though, as it does dry clear.

Anyone else perplexed by such a fine publication leaving that absent from the testing?

Dan

Dan, the FWW article described the woods, glues, joint fits and methods that were used, which allows the reader to consider the results of the tests "in context". It was a limited test, but IMO seemed to be fair and provide useful results for the conditions it covered.
FWW might be agreeable to expanding the testing in the future if they had enough reader feedback to support it.