Gluing End Grain Question???

[Don Carkhuff]

Last weekend, I attended a Woodworking Show in Chicago. Marc Adams was a speaker. For 45 degree miters and end grain applicatins, Marc said to seal the end grain with glue and to let it dry. The re-apply glue for the final joint. He said the joint would be 60% stronger. What are your views on this?
I typically apply glue only once and clamp. After the frame is dry, I installl a rip blade in the table saw and cut a flat bottom slot in the corners and insert a "spline',"feather","key" to achieve long grain to long grain strength. This has always worked well but if Marc's advice is correct, the joint should be even stronger.
What say you????

[Steve Clardy]

Yep. Very good idea. The first coat of glue will fill the end grain up some.
I usually lightly sand it then after it's dry, then recoat again, clamp it up.

[Bob Smalser]

Done all the time in deck hatches on boats. The best glue for it by far is marine epoxy because of its flexibility, as miters pull themselves apart at the corners with seasonal movement. Apply it unthickened under gentle heat foe seepage...alow to cure...scuff surface...and reglue with thickened epoxy.

That said, even with a spline or halflap it's still no substitute for a stronger glue joint in an application that will get banged around in hard use.

[Jeff Sudmeier]

I would sure think that it would help!! I have seen people do it in the past and that was their explanation as well. One person I saw do it, didn't use the splines in the miters when using this method.

[Lee Schierer]

The strongest glue I've seen for end grain was a demo at a wood show. The folks from Franklin were showing their hot melt polyurethane glue (Hi Pur). They were gluing up pieces of pine end to end and then letting folks fromt he crowd try and break the joints. I didn't see anyone succeed in breaking a joint, though many tried.

I've never tried the coat and reglue method you describe, but most end joint failures I've had were due to glue starvation, so it is probably a good method to use.

[Chris DeHut]

Back when I was a little tike, we made U-Control airplanes. I can't remember the name of the glue we used back then (perhaps that is why the glue is not longer used ;) ), but when using that glue, we always pre-glued everything. The planes were constructed of balsa wood which might be related to the end grain and miter joints in this discussion.

In soft woods (balsa) and hard wood end grain joints, the glue is absorbed into the wood very quickly, thus starving the joint of the glue. By pre-glueing, you seal the wood. Then the second application of glue does the actual bonding of the materials.

If you have not tried this, it is easy to run a quick test, I know I was the first time I tried it. The last test I did was with Oak (part of a story for an upcoming issue of the magazine). Cut two pieces of oak 3/4" x 2" x 12". On the end of one, apply glue and allow it to dry (pre-glue it). Then apply more glue to the joint and clamp it up as a T-joint (end grain to long grain) and leave it for a day.

Now try to break the joint apart. The joint will break where you expect it to, however, look closely at the breakage. In every test I have done, the long grain broke away from that board as opposed to what you would think would happen (glue line break). It is still a weak joint overall, but the pre-glueing certainly adds a lot to the bonding of the two pieces.

So, I can't say for sure if pre-glueing started with model airplanes or with conventional woodworking, but either way, the technique has been around for a long time.

Chris DeHut

[Mike Cutler]

Don. The technique used by Marc adams is termed "sizing the grain" Usually the end(s) are dampened just prior to applying the glue,the belief being that the glue will migrate further into the grain via capillary action. Once that glue has set, but not cured, another application of the same glue is applied and the joint clamped.
Polyurethane glues are supposed to excel at this. According to "Gorilla Glue" their product will migrate into end grain as much as 2 inches on either side of the joint. This is actually where polyurethanes truly outperform typical "yellow" glues.
I'll also defer to Bob Smalser's post. I believe Bob has a working knowledge of adhesives and applications that exceeds most, and certainley my experience. ;)

[Jamie Buxton]

Try Elmers ProBond Interior glue. It is a PVA, but remarkably good at bonding to end grain. I made test pieces gluing red oak 1x2 in a T shape, and then stressing the joint until it failed. The failure is always in the wood, not the glue!