I laid up a wide table of 1×6 white oak using reular yellow woodworking glue and biscuits every 5 inches. The marine varnish finish is carefully sanded to 2000 grit, super smooth. After six months the glue joints are showing as very fine ridges. I tried scraping them back with a razor blade with limited success. I think they will grow gain.
What did I do wrong? Any solution at this point?
Replies
Should have used epoxy. When the wood absorbs moisture in the summer, it swells and exerts tremendous force, It also starts to soften the glue enough that it becomes pliable and is squeezed out as you noted. Also, for glue to squeeze out, there's got to be a lot of it in the joint -- actually too much. Sounds like you got some uneven joints because this does not happen with properly edge-jointed boards. Granted, perfect joints on long boards are tough, but lack of perfection produces these results.
Did you varnish the underside as well? If not, add 3 coats to the underside and this should stop that by reducing moisture absorption. I used Titebond II on my tables and haven't had that problem but they always have 3 coats on the bottom.
Also consider that you probably put lots of glue in the biscuit groove and this stuff may still have not cured yet and could be causing swelling problems. When using biscuits on a table top, be carefull about not filling the slot with glue, which will swell the wood and cause problems. Apply glue to the biscuit only, not the slot.
Edited 8/6/2003 8:30:14 AM ET by boatman
I appreciate your suggestions. Thanks a lot.
Yellow glue creep probably contributed to your problem. Quit using yellow glue for fine furniture. It creeps, sets up too fast, and has no initial tack to assist you during a glue up. It has few (really no) attributes that recommend it to the endeavour of building furniture.
Too bad I didn't ask before the job. I'll now know better. Thank you.
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 adhesive (white and yellow glue) 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.
For panel glueups I use a urea formaldahyde adhesive like DAP/Weldwood Plastic Resin. Hide glue also has no creep.
Thanks for the good information. I'll try Weldwood next time.
I hate to be contrary here, but 25 years of furniture factory experience tells me your problem has nothing to do with the glue. Most furniture factories I am familiar with (up to about 15 years ago) used various forms of PVA or alipahitic (yellow) glue for all their panel glue ups, with no problems at all. Even the RF panel driers used a type of PVA.
The problem of raised glue joints usually arises when the wood shrinks and the glue line stays the same width. The wood shrinks away from the glue, leaving the glue line a bit proud of the surface. In this case a rigid glue line would make the problem worse, and a little creep might be beneficial.
Creep is when a glue line gives, or moves under load. Bad for veneering. Maybe not so bad for joinery where the glue can accomodate a little seasonal wood movement. I fix a lot of furniture (especially chairs) that has been glued together with rigid glue, and the glue has let go of one side or another within a couple of years.
PVA and yellow glues also tend to have good shock resistance, which can be a nice feature, too.
Michael R.
It's good to hear another possibility. I'll stay tuned. This is getting interesting.
It's simply a fact that hide glue and the other glue(s) mentioned are more creep resistant than PVAs. Whether or not your problem WAS caused by glue creep is up for debate, the fact that glue creep is almost always a bad thing is not up for debate. In the future, doesn't it makes sense to eliminate a potential problem before it happens?
You have the facts, you make the decision.
Your fix is to strip the piece and use a non film forming finish on your project, OR refinish with spar varnish which is more flexible due to its designed formulation.
There is a difference between consumer grade PVA's and those made specifically for the furniture trade. And, the problem is more prevelent in areas with high swings in long term relative humidity.
In the shop I was involved with, we manufactured a line of semi-custom furniture for an interior designer to the "carriage trade". We spent lots of time with our commercial adhesives supplier working on the problem of raised glue lines. There were a number of reformulations but none completely eliminated the possibility of future problems.
For panel glue ups, we went to urea formaldahyde adhesives and had no further problems.
PVA adhesives are the best--and safest--all round adhesive currently available. But, for certain applications, their propensity for creep is a shortcoming.
Howie, you're right about commercial formulations being different than consuumer formulations. I ran a factory that ate up over 3,000,000 board feet of pine per year for nearly twenty years, and, later, another one that made all the 8/4 oak table tops for a very large chain of restaurants across the country (Talk about a challenge!). I was the guy that specified and bought the glue, and engineered all the gluing and assembly processes, among other things. As far as I could tell, there wasn't much difference between the performance of industrial vs consumer glues, whether yellow or white. What they did for us was to vary the viscosity, open time, tack, color, etc.
I agree with you that PVA (and Yellow) clues are the best and safest all around glues available. If there were something more cost effective available, most of the big factories would be using it. However, not only creep can be a problem, but lack of heat and water resistance, and lack of gap filling ability (optimum glue line is @.003 in.) As you probably also do, I use U/F glues for veneering, epoxies when I need gap filling qualities, and hide glue when working with period furniture or when the glues might need to be re-activated, such as on veneer repairs. Even use a little HotStuff once in a while.
All that said, I find it difficult to connect the type of glue with raised glue lines. There is an opposite penomenon called sunken glue lines. It happens when you plane panels too soon after glue-up. The wood is still a little bit swollen near the joint from moisture absorbed from the glue and shrinks back after processing, leaving depressed areas along the glue lnes. Perhaps the solution to your problem came from a coincidental change in the moisture content in the wood you were getting, or from environments changes. I couldn't swear to it because I wasn't there, but that would be my best guess, based on experience.
Good joinery makes creep less of a problem, and shock resistance and the ability to move a little with the wood can be a good tradeoff. I would not, however, use PVA or yellow glue in an assembly that was under constant strain, such as tension, or shear loads, or on veneers.
Michael R
I've used WW II PVA for 20 yrs, and only had the glue line problem once, on a 9' cherry table top. I put it down to wood which was probably unevenly dried. Ive used PVA glue on oak, cherry, alder, walnut, honduras mahogany, yellowheart and bloodwood w/o problems. Every 5" for biscuits is probably too many. I space them about 15-18", and they're only there to help line up while clamping. The glue's plenty strong w/o the biscuits, for a flat tabletop.
I am overwhelmed by all this good advice. You guys are great! Thank you all.
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