Help a veneer newbie- swollen joints?

[Jeremy Chisholm]

I've undertaken my first veneer project that requires joining multiple sheets of veneer (for an important client...LOML!). The the layout, surfact prep, cutting and edge jointing process has (I think) gone very well. But after unclamping my first glue-up, I've got a mess on my hands. Thankfully I have lots more veneer, so the project is not a loss, but before trying again I thought I'd ask the experts for advice.

The basic problem is that the joints have swollen, forcing the edges of the panels up from the surface of the substrate. The veneer is VERY curly curly maple (~3/64"), the substrate is 1/2 MDF, glue is Titebond cold-press veneer glue. Joints are taped in back with Woodcraft 3-hole veneer tape.

My setup, viewed from above, is respresented in the diagram below. The dashed line is the perimeter of the panel I'm gluing, the diagonal lines are the joints between the veneer panels, which have now swollen. The outer solid rectangle represents the perimiter of the two faces of my "press", each 3/4 MDF. The blue boxes are clamping cauls, the red circles bar clamps. On top of the panel I've stacked about 300 lbs of concrete blocks.

Any thoughts? Is the problem with my makeshift clamping setup? It's worked for less complicated (ie single small sheet) projects, first time for this kind of glue up. Or Something else I'm missing?

TIA,

JC

[Joe Jensen]

Can you explain what you mean by "swelled" in more detail? It's just me, but I've never had much luck with the veneer tape. I now run a line of blue painters tape on the joint to completely cover it. I then fold the sheets alone the tape line to expose the two edges of veneer and I use my finger to run a VERY small bead of glue along the joint. I then unfold the sheets and tape the other side. After 20 minutes or so, I untape them and lightly scrape the excess glue off. This way I end up with a single sheet of veneer to apply to the substrate...joe

[Jeremy Chisholm]

thanks Joe, I think I'll try that on a couple test pieces.

By swollen I mean that the joint has puckered up to form a peak or ridge, running the full length of the joint. The top fo the "ridge" is about .20" above the rest of the veneered surface. The veneer has pulled away from the MDF.

It looks like the veneer is "growing" across the grain (and then buckling upward when it runs into the next piece of wood at the joint) as you might see wood move when humid, but on a much more drastic scale than any movement I've seen before. This has led me to suspect the wood is soaking up too much moisture from the glue or tape? I spread the glue with a roller, not sure what else to speculate...

THanks,

JC

[Mitchell Andrus]

I do a fair amount of veneering and inlay work and have 'almost' completely eliminated swelling problems.

First, make sure the veneer is flat. Un-wrinkling veneer in the press during glue-down is too late to fix anthing going wrong and will cause the veneer to expand and 'tent' at the joints.

Second, use proper veneer glue. They've got more solids than regular glues.

Third, when making a panel more than 10" wide, I leave a very small gap between parts so when they swell, the gap closes and doesn't tent.

Forth, I let the glue 'tack up' on the substrate for a few minutes. Drier glue causes less swelling.

Fifth, I use a vacuum press/bag. I cover the face of the piece with paper towel to keep the bag clean and soak up any squeeze out and I roll the face as it vacs and for a few minutes longer as it settles in. I know not all of us can use a vac press, but it really is the way to go in order to get control of the glue up during the process.

When working with woods that really like to swell, wet the parts and assemble the piece slightly damp, pre-swelling the parts.

Also, 300 pounds doesn't sound like enough pressure. Without factoring in the clamps and assuming the area is about 300 square inches, this is only 1 psi. If you can't go vacuum, make a rig and use a hydraulic car jack.

Mitch

[Mike Henderson]

I'm certainly not a veneer expert but here's some suggestions:

1. If the veneer is not flat, you should flatten and size it before use. The sizing will help to strengthen the veneer which is useful for burls. One flattening solution is 4 parts water, 2 parts white glue, 1 part alcohol, and 1 part glycerin. The glycerin causes the veneer to retain some water so you don't get the big swing between wet and dry veneer. You can find other recipes for flattening solution on the web or you can buy commercially prepared flattening solution. When you're ready to flatten, brush the solution on to the veneer with a paintbrush - both sides. Put the veneer between two pieces of plywood as follows: Plywood, paper, window screen, veneer, window screen, paper, window screen, veneer, window screen, paper, (continue this sequence for all pieces of veneer treated), plywood. Do not use newspaper because the ink will transfer to the veneer. The window screen is used to keep the veneer from sticking to the paper since the flattening solution contains glue.
Change the paper after about an hour, again after maybe four hours, and at least daily after that. When the veneer is no longer "wet" take the window screen out and continue drying with the paper. Dry for a minimum of three days. When the window screen is in the stack, don't clamp the plywood or the window screen will imprint on the veneer - just put some weight, such as a few bricks, on the plywood. Once you remove the screen, use clamps to clamp the plywood. Once the veneer is dry, store it between plywood or cardboard to keep it flat until you're ready to use it.

2. If the panel is not too large, use torsion boxes to clamp the veneer. Use 6 mil plastic between the veneer and the torsion boxes to keep the panel from sticking to the torsion box. If you used multiple types of veneer with different thickness, add some thick cloth, like duck cloth, to the clamping. The sequence will be torsion box, duck cloth, plastic, veneered panel, plastic, cloth, torsion box. The problem with torsion boxes is that they get heavy in large sizes, maybe beyond 3' by 3'.

3. For larger panels, use a vacuum bag. While you can press with the bag directly on the veneer, you can experience problems that way. If the bag has a ripple in it, the spot under the ripple will not press on the veneer and you'll get a bubble in that spot. You may have to look at it in glancing light to see it. A technique that avoids this problem is to use a caul on top of the veneer, with 6 mil plastic between the panel and the caul. Make sure ALL the edges on the top of the caul are eased or you'll get stretches in the bag that won't go away. The caul should be just slightly larger than the panel which often means you have to cut the caul special for that job (which is the reason many people don't use a caul). Note, a caul is just something like 3/4 inch MDF.

And just a point for clarification. You said the veneer tape was on the back of the veneer. The veneer tape should be on the show face of the veneer. After pressing, you can easily remove it by misting it and peeling it off after the water soaks in well.

Good luck,
Mike

[Earl Kelly]

Jeremy,

300lbs is not near enough pressure. If your panel was approx. 2'x3' you'd only have 50lbs per sf. See if you can figure out a way to clamp your panel up with cauls and battens.

I only use the tape on the glue side for shelves and interior components, never on a face piece.

[Mike Henderson]

The reason you put veneer tape on the show face and not on the glue face is that the veneering glue will stick to the veneer tape and not to the veneer. The veneer is then held down by the glue in the veneer tape which is water solulable and not that strong. The only thing that saves people who do this is that most veneer tape has holes in it and the veneer glue can grab the veneer where the holes are.

There should be nothing on the glue face except veneer when you glue it up. Veneer tape goes on the show face and is removed after glueing.

Mike

Added note: Also, if you have a complex piece with overlapping veneer tape, maybe four or so layers thick, you'll get a bump where the tape is if you put the veneer tape on the glue face. Save yourself a lot of grief and put your veneer tape only on the show face.

[Charlie Plesums]

The advice already given on how to avoid future problems sounds excellent... I only want to add a comment on what may have happened...

When I tried a "different" veneer glue, it dried faster than I expected, especially at the joints, which then puckered up during sanding, after pressing. I had a terrible time getting more glue under the edges along the joint lines. I think you may have had glue problems like that. Also, if the veneer tape was on the glue side, you definitely had low adhesion at the joints.

Remember that a vacuum press removes most of the atmospheric pressure, so the pressure is most of the 15 pounds per square inch of atmospheric pressure. Not quite all - the vacuum isn't perfect, but figure about 1700-2000 pounds per square foot. If you parked a car on a one square foot project, the pressure wouldn't be enough.

[John Lucas]

And something else to add to the comments above, you may have unclamped too soon. The joint should have been absolutely flat and dry...a couple of days if necessary.

[Mike Henderson]

One more piece of advice. If you're new to veneering, make a few test panels before you do your furniture. Make a piece of substrate (MDF is good) maybe 3/4 inch thick and maybe 12 inches by 12 inches - 1/2 inch is a bit on the thin side. Do some joints like the ones you're having trouble with. Put your veneer tape on the show face. You can use blue painter's tape on the glue face to temporarily hold the veneer together until you get the veneer tape on the show face (you always work on the glue face when fitting the veneer). Make SURE you remove all the blue tape before gluing.

Use whatever glue you plan to use on your furniture. Use the same clamping technique you plan to use. Use plastic between the panel and the caul - sometimes glue leaks through the veneer and will glue the panel to the caul.

As John mentioned, leave the test panels in clamps long enough to be sure the glue is dry and hard. Urea formalyde is a good glue for veneer but you should leave it in clamps at least 14 hours - and more wouldn't hurt.

You can run into different problems when you do large panels but you'll learn a lot on the small panels. Make your mistakes on cheap stuff and not on your furniture.

Good luck,
Mike