# What happens when we clamp glued joints?



## chiuchimu (Jul 2, 2014)

When we clamp a joint while gluing it is generally stronger. However, there has been times when I glued without clamping and the joint was very strong - stronger than the wood. I've had the wood break instead of the glue joint even though the pieces weren't clamped.



So I'm asking what do you think happens during clamping that makes the joint stronger? Is it?


1) it makes better contact by lessening any gaps between the wood pieces.
2) Presses the glue deeper into the wood.
3) Removes as much excise glue as possible.


I think knowing the exact machinism that makes clamping joints stronger can lead to methods that make joints even stronger. For example, if its the deeper penetration of the glue that makes the joint stronger then we can try maximizing it by thinning out the glue to penetrate deeper or using a vacuum chamber to suck the glue deep into the wood.


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## redeared (Feb 7, 2019)

I go with 1 and 3, I don't use excess pressure when clamping


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## Steve Neul (Sep 2, 2011)

chiuchimu said:


> When we clamp a joint while gluing it is generally stronger. However, there has been times when I glued without clamping and the joint was very strong - stronger than the wood. I've had the wood break instead of the glue joint even though the pieces weren't clamped.
> 
> 
> 
> ...


The clamp doesn't press the glue into the grain of the wood. All that is really needed is a snug fit. Often that requires clamps if what you are gluing resists pulling together. You can use too much pressure and force too much glue out of the joint making the joint weaker. 

The excess glue is best washed off with a wet rag while it's still wet. Glue left on the surface can soak into the wood sealing it to where if you don't sand it enough can prevent the wood from staining.


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## woodnthings (Jan 24, 2009)

*This guy did a test on gluing joints*

By applying different amounts of glue in the joints his results were surprising. Look in at 4:40 to see the results:


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## chiuchimu (Jul 2, 2014)

woodnthings said:


> By applying different amounts of glue in the joints his results were surprising. Look in at 4:40 to see the results:
> 
> 
> Can you squeeze all the glue out of a joint? - YouTube


 Thanks. I watch a lot of Wandel videos, it's uprising how I missed this one.


So it seems good contact between wood is not only unnecessary but makes the joint weaker. Fascinating. As I originally posted, I found it strange that sometimes glued but not clamped pieces are very strong. Now I know why. It's the glue and good adhesion of glue to wood that matters not the close contact between wood pieces. Clamping down actually pushes glue out of the joint making it weaker. Ofcourse I'm still going to clamp down on the joints because I want a nice tight clean joint but now I know it doesn't help with the strength of the joint. I might try chiselling out a shallow patch in the joint and see how that works. See when this "glue gap" method works instead of other methods like dowels or rabbit joint.


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## unburled (Mar 10, 2019)

It be interesting to hear his thoughts on the results and how they compare to glue mfr testing, how he might do the testing differently, and one-year-out testing.

https://i.imgur.com/RWtCcm

1.png


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