I have just finished a large maple glue up. Each board is 1.5″ thick, 7′ long and range in widths between 8″-11″, for a total width of 48″. The top has been a beast to work with considering my 6″ jointer and small facilities. I decided to belt sand the top outside (dust issue). After a couple hours of sanding the top looked great. I decided to leave the table on my deck with a large tarp covering it. 2-3 days later I removed the tarp to do some more work and found that the boards were seperating (ie. along the glue line) at the ends of the boards–ahhh ! I brought the pipe clamp to see if it would come back together under moderate pressure. unfortunately, it would not move. I’m wanting to know the theories out there before I start all over (I have opted to start a new top as opposed to reripping and glue etc….). I’m wanting to know if anyone thinks this could be related to the sudden rise in temperature that the table experienced. That is, the wood was stored in my cool basement and it sat in very warm temperatures outside as I worked on it. Also could it be I applied to much pressure to the boards during glue-up thereby starving the joint of glue.
Any ideas would be appreciated.
p.s. I will save the original by removing 3″Off the ends and replacing it with a breadboard edge. Unfortunately, this customer does not want a bread board edge.
Thanks N.E.T.
Replies
Okay, Net. Answer these questions and maybe we'll eventually get to the meat of the problem.
1. Did you use PVA? Did you use hide glue? What type of glue did you use, and how?
2. Did you do a sprung joint?
3. Did you use alignment aids such as biscuits?
4. Did you glue up the top in one go, or do it stages?
5. Where do you live, and by that I mean, how different are your workshop conditions to the outside conditions? Do you live in a very humid climate, for instance, or very dry?
6. Was sun beating down on the temporary tarpaulin?
7. Did you let the wood acclimatise for a couple of weeks to your workshop conditions prior to getting at it to make the table top.
8. When applying pressure on the business end of the cramps, did beads of perspiration appear on your forehead due to the effort involved? Nothing to do with it being hot anyway.
All the above are serious questions, but I might have forgotten to ask a few. Slainte.
Website The poster formerly known as Sgian Dubh
Richard
1. Yellow carpenter glue
2. No the joints were flush
3. 2-#20 biscuits every 8"-10"
4. Stages
5. Westcoast (Canada)
6. The tarp would receive direct sun from 3:00pm on (bottom line it would have been hot especially compared to the basement)
7. Yes 5 weeks
8. I would like to say I used light pressure however there is the possibility that I tighten up too much. During the dry fit the boards fit nicely, perhaps there may have been a minor gap at the edge (speculation) however it would have been slight.
I have done many glue- ups and have never had such an experience, that is why I am leaning towards the outside conditions.
Hope that gives you something to work with
N.E.T.
It seems like the table top went from a relatively humid basement to a much dryer outside. The ends lost moisture resulting in the shrinkage and board separation. Have you tried bringing it back to the basement for a few days? Another possibility is not using enough glue, but that would not be the primary cause (but the change in relative humidity makes it worse).
Ben
I had moved the top to the basement the moment I discovered the problem (24 hours ago). I definetly used enough glue, however I'm wondering how likely it is that I squeezed out too much of the glue by applying too much pressure on the ends.
thanks N.E.T.
How long were the boards in clamps, between stages? How old is the glue?
I'm also thinking that perhaps, if the tarp covered the top of the tabletop but the tabletop was perched on, say, a pair of sawhorses, the difference in the air circulating around the top and bottom may have caused some unequal drying/dampening. That might have been enough stress to pull the joints apart, if the glue was close to failure for other reasons (old glue, joint line not sprung, etc.).
David"The world that was not made is not won by what is done" -- Mundaka Upanishad
Davamoore
Wouldn't such conditions result in cupping as opposed to the boards separating? The boards were left in clamps for at least 5hrs. Just for the record, the glue is new.
Thanks N.E.T.
Edited 6/6/2003 11:15:58 AM ET by Not enough time
Sounds to me to be a problem of wood shrinkage due to changing wood moisture content as a function of changing EMC conditions (warm, dry, more air movement outside versus cool, damp, static air flow inside).
End grain drying rates are about 10 times greater than flat surfaces. The adhesive was still probably still relatively soft and as a result you had glue line failure, which I suppose is better than have wood failure (cracks and breakage).
Assuming I have a moisture problem based on the sudden change does anyone have any suggestions. As previously noted I was planning on constructing a new top however I'm starting to wonder if I may be able to remedy this problem. For instance, would anyone consider using a humidifier to reverse the process and then reglue?
p.s. how do I add to the discussion without replying to a particular individual. My first post says to ALL to start the discussion but how do I do this once the discussion has begun?
Thanks N.E.T.
I am in the camp that believes the change in atmosphere caused your newly bonded joints to fail. If acclimating stock to workshop conditions is important, then we must assume those conditions should be held soon after construction. And, any drastic change in conditions will probably result in some sort of structural change.
To further your quest into the truth of this matter, I suggest that you conduct an experiment. Take a few sets of boards and with careful preparation repeat the prior glue-up and surfacing, to see if it happens again. With another set, glue-up and surface as before, then move the piece back into the shop. Do likewise in as many permutations as you have time, energy, wood, and interest. Your direct experimentation will move you a long way toward understanding this situation.
I guess my earlier reply did not get posted.
I think that if you return the top to the basement, the ends will readsorb moisture and the cracks will close. However this will not reestablish a suitable glue joint.
You probably are going to have to rip the top along the glue line and rejoin/reglue (after a suitable period of aclimitazation).
Whenever I do table tops, I always put a "butterfly" into the joint about one inch from the ends. If the client does not what it visible on the top surface then I do it on the underside. I feel that addition feature adds considerable strength in situations just as happened to you.
I am not an advocate of sprung gluelines. It might be benefical for end grain drying but there is equal probability the wood will adsorb moisture. In such conditions a sprung glueline puts more stress on the joint but in a different location.
Looking at one of your old postings, What is a butterfly? Thanks much
It is not an insect -- I now refer to them as flutter-by's (which I think is more appropriate).
Think instead of the form of a bow tie -- two opposing dovetails cut from a single piece of straight grained material about 0.25 inches thick that is then "inlaid" into the top across the joint with the thinnest part of the piece is at the joint line.
The opposing angled edges secure the joint and prevent it from spreading.
Thanks, I'v seen those but didn't know what were called.
I see no mention of moisture content! Can you be sure all the boards are of the same moisture content? Air dried or kiln dried? 7% is the recommended range for furniture.
Yes I'm sure
Thanks N.E.T.
Way back when, jointers sometimes had a lever which was to be used on the last edge pass, and it left the baords very slightly cupped, with the middle narrower than the ends. The theory was that the moisture left the endgrain faster, and thus a bit of shrinkage would not open the joint. Hence, the name "sprung" joint. This was for a time when there was greater variation between conditions, summer to winter. Last jointers to have those, I think I read somewhere, was in the 30's or so. My old 1925 or so jointer has this lever, but I have never tried to use it. I would tend to think that the more suden drying from the end grain was the culprit.
Them are some purdy cues. They sure won't make me play any better. By the way, what are the legal lenght/weight specs for a cue, if any?
Pardon?N.E.T.
OOOPS... replied to the wrong post. Duhhh.
ya I figured so I just couldn't resist.
Rather than dealing with the mechanics of the whole thing, with the sun shining on the tarp, you created a very warm and damp environment. This would have been exacerbated if the tarp was a dark color. PV glues take quite a while to develop full strength and moisture and heat can cause it to weaken. In fact, moisture and heat is how you separate PV glued joints for disassembly. That, and the movement of the wood as it changed its moisture content is what probably caused the problem.
As to "starving a joint" that is almost impossible in a small workshop. To develop full strength in a glue joint in hardwood, 100-200 psi is required. For your glue up, that translates into 10-12 tons of pressure. A pipe clamp exerts about 1/2 ton so you would need 20-30 pipe clamps fully tightened for optimal strength. So, you have little to worry about starving the joint. In fact, just tightening the clamps until you got squeeze out means you have a weak joint. PV and other water based glue has no inherent strength. Wood fibers soaked in PV adhesive and brought into the closest possible contact is where the strength is derived.
In the shop I was involved with, on large panels, we used a hydraulic press. Of course, we didn't use PV adhesives because of some other problems. But, we did not do any machining on the panels for 4-5 days to give the adhesive time to fully cure.
Panels should be treated very carefully for as long as you can.
NET,
What happened was simple and was already covered by another response, the intense hot dry conditions in the sun caused the ends of the boards to lose moisture very quickly and the first few inches of each board shrank. No matter how the boards were prepared, or the type of glue used, or whether or not the stock was kiln dried, the boards would have shrunk, this is wood working reality #1. Once the boards did shrink, either the joints or the boards would have cracked, nothing could have prevented it.
If you bring the top back inside, the boards will reabsorb moisture from the air and, in a few days, the joints will close up. You won't have to cut the ends off the boards to salvage them, but the joints will need to be reglued, which will require you to saw the top apart along the joint lines and start all over again.
The fact that the joints broke rather than the boards splitting does suggest that the joints were glue starved. To prevent over rapid drying though the end grain of the top before it is finished, you can wrap the edges of the top with any kind of plastic packing tape or duct tape.
John W.
I wouldn't rule out the belt sanding as a contributor to the problem. Wood reacts the same way as steel to vibration - it releases the stress in the lumber. I've had plenty of stuff react to agrressive sanding.
I agree with what John W says. I'd also add that moving from one environment to another is asking for trouble unless you have better control of the second environment. Once the glue cures you should get some finish on that baby as quickly as you can. All six sides. If you have to leave it for any time it should be stickered and weighted to hold it flat or you may have more flattening work ahead. You mentioned the possibility of a slight gap present. While thay may not be the sole cause for catastrophe it certainly could be a major culprit. When mated, two jointed boards should slide together seamlessly without glue. Good luck.
There are more old drunkards than old doctors. Ben Franklin
Outside, under a tarp?
Haven't you answered your own question. And Maple, to boot. Not good.
Bring the panel back in. Let it sit for two weeks. Rip it apart and re-glue, as another poster mentioned.
Don't store furniture parts outside.
Lately, I've taken a liking to gluing up panels at least 12" over length. At least. May be a waste of material, but a timesaver if I can lop a problem off in a few seconds.
I also try to glue a project's big panels at least three weeks before I know I'll need them.
It is impossible to be too conservative with a tabletop glue-up. I've learned the hard way.
Edited 5/15/2006 11:04 am ET by charlesstanford
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