Latest from the Titebond tech team:

 

The results from yesterday’s poll are in! We asked lead glue guru Bob Behnke (who manages our Technical Support Team) to weigh in on it. He says there’s no right answer; both approaches have their benefits and drawbacks. Here they are:

One-sided gluing is the only way to get invisible glue lines and results in less squeeze-out mess. On the other hand, you must be quick to join the parts within recommended open and assembly times (which can, themselves, be cut in half by less than 8% wood moisture content).

Two-sided gluing results in higher amounts of glue and more water in the glue, which extends working time. On the downside, gluing two sides results in thicker glue lines and a lot more squeeze out. You also use more glue than necessary. (We’d rather you put that extra glue to good use!)

There you have it!

Sounds like from the last two sentences they prefer one side and that is what I vote for. 

I mostly do one side.  If I am looking for most strength I do both sides to be sure it soaks in each piece some.  Just my opinion, no science behind it.

I think it depends on what I'm gluing. I don't mess around trying to spread and then join the pieces, so I don't think I have issues with it drying too much usually.

But if I'm not 100% sure I've got enough coverage I might use it on both pieces, like a rough mortise and tenon (which mine still can be, still practising), just to help that bond.

But usually only then.

With my rolling pins I always use 2 sided. The longer open time assures the inserts don't seize during installation. 

For most jobs I just do single side. If it involves end grain in any way then it’s definitely two sides. 
Paul

21 minutes ago, Masonsailor said:

For most jobs I just do single side. If it involves end grain in any way then it’s definitely two sides. 
Paul

I seize..or is it size?... end grain. put a dab on the end grain and rub it in till its no longer liquid. Then, apply glue as normal. That way, you're pretty sure the end grain won't soak up the glue, starving the joint.

One side has long been my practice, though if gluing to the edge of plywood (like edge banding) I'll usually coat both sides. This is based on absolutely no scientific or other evidence that it's better. But I will say this...I've never had a piece of edge banding fall off!

Edited June 10, 20214 yr by Fred W. Hargis Jr

My practice has been to apply to both sides, but I may change now!

This is all based upon a poll.  Are there any tests that have been conducted that might show any difference in joint strength?

To many variables for me to say one side or both. When edge banding plywood I do both to insure good bond. Same for end grain work.

I don't see much science here.  I'd think that wood species and/or grain configuration makes a big difference.  Also the glue type, moisture content and relative surfaces smoothness play a role.  

 

Having listened to all opinions and after consulting my horoscope, I flip a coin.  

After reading the responses I will add. If gluing to a porous surface as ply or endgrain , more glue will be needed. I do very little of that kind of gluing. But I do believe that one surface glued is all that is needed for long grain.

19 hours ago, Gene Howe said:

I seize..or is it size?... end grain. put a dab on the end grain and rub it in till its no longer liquid. Then, apply glue as normal. That way, you're pretty sure the end grain won't soak up the glue, starving the joint.

I have used "Quick and Thick" on butt and miter joints where there is short grain.   It is very thick, almost like paste (or sour cream).  Bob Behnke gave a demo locally where he used it to glue two 1x2 poplar boards end grain to end grain.  In about 20 minutes it was hard enough he couldn't bust it apart without putting on a bridge and stepping on it.

 

I have not tried the Extend product yet, though if I was still doing chair regluing, I'd give it a try.  I generally used white or liquid hide glue (depending on the original glue used) to give me some more closed assembly time.

 

The article, as I read it, said there are pros and cons to one- or two-sided gluing, so whatever is more important to you.  Like Lew said he uses 2 sided so he get some more time, and since he will be turning the edges, extra squeeze-out is not an issue,

Always 2 sides for me.  I tried one side once and some of it didn't fill in the gaps completely.  Squeeze out is not a problem and my seams hardly show.  When I do an ornament, folks will look and ask how I turned the inside.  When I point out the seams, then they realize that it does have joints.  Just the way I do stuff.  

One side seems to work for me.  Some other glue types require both sides (contact cement) so maybe the truth is, it depends on the context.  With any glue, technique is important.  100% coverage applied evenly has been most successful for me.  I use squeeze out as a guide with yellow wood glues.  If it's not squeezing out, there isn't enough glue.

 

.40

Both sides. Hot water and a rag takes care of squeeze out and never have I had a joint come apart.