Glue joint creep

[jared herbert]

At least thats what I think it should be called. I have made many things over the years with edge glued oak sides, tops etc. with never a problem. This winter my daughter wanted a coffee table for her new town house that she just bought. So I made one, in February, in my heated shop in Iowa. I used 3/4 inch oak with biskets to help with alignment and titebond glue. Every thing went just fine and the table was delivered to her in April. I recently visited her place and checked out the table as I always do with things I make. I could feel every joint in the top. It is not visually apparent but you can sure feel the joints with your fingertip. I have never had this problem before or at least not noticed it. Now the question, how do I avoid this in the future and what did I do wrong. Was the lumber not dry enough or not dried correctly? I did have it in my shop for several days before I used it. The lumber came from Missouri originally and was stored in a heated garage when I bought it. Did I not allow the glue to cure long enough before I sanded and assembled the table? I think it was at least a week from glue up to final assembly. Was it the fault of the glue? Or just bad luck? Any input would be appreciated. thanks in advance. Jared

[Jamie Buxton]

Use less glue, and more clamp pressure. Seriously. If you can feel every joint, it is not just one or two boards moving around. It is likely the glue line extruding out of the joint, and doing it everyplace. You can get less of this effect by having thinner glue lines. You can get this with less glue and more clamp pressure.


Or you could use a non-creeping glue like epoxy or urea-formaldehyde. They're two-part glues, so they're a hassle. But they don't creep.

[Howard Acheson]

Here is the best write-up I have seen on the issue.

QUOTE

Creep has been known about for many years, perhaps even centuries. It's nothing new and has already been defined precisely, so no need to reinvent the wheel here. PVA is the classic and renowned creeper.

The tendency of the glue to ooze out of joints is one form of creep. A classic example is in a slab edge to edge glueup, such as a table top. When ambient humidity rises the timber and the the glue swell. When the ambient humidity goes down the timber shrinks again, and so does the glue, but the glue doesn't all shrink back into its original place resulting in a line of pimples disfiguring the finish. Actually, under sustained high humidity my anecdotal observations are that the glue keeps on absorbing moisture and creeps out of the joint without the need for the timber to shrink. The symptoms can also be seen sometimes at the shoulder line of other joints such as mortise and tenons.

Another cause that I've witnessed several times is to make a solid timber slab with edge joints in a fairly humid workshop without climate control using PVA as described before. Then right away get to planing and preparing the surface ready for polishing with scrapers, sanding, etc.. Right after that apply the polish, whether it be varnish, pre-cat, or another finish, and take the piece into a drier house, either heated or air conditioned. Three to five days later the rows of pimples will be apparent as the timber shrinks.

Somewhat related to this is using an aid for edge glue alignment, such as biscuits with PVA. These jobs need time to settle. If you are in too much of a hurry and prepare for and polish it all as soon as you get the piece out of the clamps, the chances are you'll see a row of rugby ball shaped depressions telegraphing the position of every biscuit a couple or three weeks later, although I've seen them appear as much as a year, or more, later. The moisture in the glue swells the wood either side of the biscuit, and it takes a week or two for this moisture to work its way out of the joint properly. My advice then is to not rush into the preparing for and polishing stages after this type of glueup, particularly table tops and the like which show off every flaw. I don't use PVA for this specific kind of glueup at all anymore here in hot, humid Houston. I tend to reach for the hide glue nowadays, either out of the pot, or the liquid stuff.

Slainte, RJ (Richard Jones)

CLOSE QUOTE

[David Thompson 27577]

Might be glue creep.

Might not be. If the individual boards you used were of varying grain density, then they will react to humidity differently. And if some were quartersawn, and others not, the same will be true.

If the problem is glue creep, then when you feel a "rising" joint on the top of the table, you should feel a "rising" joint on the underside -- both the top and bottom of the board moved up, compared to the adjoining board.

If it's unequal expansion, one board will be thinner than it's mate on boththe top and bottom.

[jared herbert]

The glue joint creep is more like a line rather than small globs. Maybe I do use too much glue, I tend to err on the side of heavy rather than light. I have another table top that I am working on now. It was glued up several, probably more than 4 weeks ago and I just sanded it yesterday. The wood is probably carrying more moisture now as it has been wet and raining for 6+ days now. Thanks for the info Jared

[Ray McCullie]

I don't know about everyone else but I'm in Missouri and it's hard to find stable wood sometimes. The weather is so up and down here that unless they really stayed on top of it while in storage it's MC could be all over the place. Do you check your stuff with a moisture meter?