Veneer Issue

Re: Veneer Issue

Tom Stockton

CJ

I've had really good luck using an iron to press bubbles down. Works best the first day or two after pressing.

Pretty easy to do just set iron on a hot setting and press down moving the iron so you don't burn stuff. You will get a little darkening but it should sand out, unless you really char it. The only place I wouldn't try it is on seams because the heat will open them. This won't work with urea formaldehyde type glues

good luck

Tom

Re: Veneer Issue

Dick Coers

I don't have any idea what that glue is. A quick Google only reveals that Joe Woodworker helped develop it and he loves it, and it sets fast. So no idea how to reactivate it or if heat will reset it.

I always apply glue to the substrate and the veneer in that order with a rubber roller. I always cut a backer from melamine to distribute the pressure over the entire panel.

Do you know what kind of adhesive that really is?

Re: Veneer Issue

Ellis Walentine

Injecting glue can leave an obtrusive mark, particularly on light-colored veneers. My method for fixing veneer bubbles was to make an unobtrusive slice into them, along grain lines if possible, and then work some glue into the slit with a finger, then clamping with wax paper. I modified an Exacto knife blade to do the slicing, grinding and honing all edges thin and razor sharp and blunting the tip slightly.

If you can experiment with the ironing method, and it works, that would be easier.

Ellis

the problem with all these fixes

Bill Tindall, E.Tn.

You all have used them with a glue you knew something about and had an inkling of why there was a bubble. If there is insufficient glue ironing won't work, nor if the glue is a crosslinking glue. If there was plenty of glue and insufficient pressure new glue may or may not stick to cured glue.

I hope the lesson learned is to emulate what a professional shop does. It will be quick and reliable. With all the professional experience with veneering on this Forum it is sad that someone went to the internet to get advice. Maybe the place to get advice on how to fix this glue is from the person that recommended it in the first place.

In the Headley shop we used white glue and slathered it on with a paint brush to both sides. I have continued this practice and never had a failure.

Re: Veneer Issue

Sgian Dubh

I've just completed a veneering job of approximately 65 m² (~700 ft²) working as a sub-contractor for a furniture business. Seventeen wardrobe doors roughly 2.8 m X 450 mm wide with walnut veneer both sides, a bunch of assorted wall panels with show veneer and and backing veneer, plus four quarter circle arc pilasters with an arc radius of about 100 mm, and other odds and ends. The methodology was hand cutting with knife, veneer saw and no 5 plane, slather on Titebond veneer adhesive (the brown stuff) with a hoppered roller and shove the panel into a vac-bag.

I'll probably never see the finished dressing room because other contractors made the cabinets and are installing my work, so there are unlikely to be any photos too, much to my disappointment.

Still, as you can imagine, there were opportunities for glue ups to go wrong, even with all the professional equipment and my decades of experience brought to bear on the task ... and they did, three times. For whatever reason there were two panels and one pilaster where the adhesive partially failed resulting in bubbles and blisters. The first cock-up resulted in me trying some of the common suggestions already made, e.g., a slit, squeeze in adhesive, and iron down, or just iron without slitting. After about an hour of tinkering about like this I decided to abandon the repair attempts because it was obvious these techniques just weren't going to be satisfactory, resulting in stripping all three failures and reveneering from scratch.

Sometimes, the drastic approach, i.e., starting from scratch again is the quickest and most satisfactory solution, but in your case, hopefully some the repair suggestions provided will work ... but, all the same, I wouldn't be too optimistic, ha, ha. Slainte.

Re: Veneer Issue

CJ in MPLS

Thanks for the advice. I did not get to the ironing as I was finishing up a work table, but that is now complete AND my wife has assented to using the household iron on the veneer. I'll let you know how it goes, but the reason I did ask for assistance was that I do know that starting over on that panel is probably the correct answer.

Cheers.

Re: Veneer Issue

Frank House

When you stripped the failed panels, did you find any hint of the failure mechanism?

Frank.

yes tell us more

Bill Tindall, E.Tn.

It is worrisome that an experienced professional can get veneer failures. Any insight on what went wrong? Vacuum or clamp pressure?

Re: yes tell us more

Sgian Dubh

Failures of adhesion? I reckon to experience between about 3 - 5% failure with veneering in a vac-bag, or hydraulic or vacuum press, whether heated or cold. For small one-of jobs that's once every now and then, but for larger jobs including matching and joining edges and the like, it can be seen that if you're dealing with roughly 65± m² you might experience failure on maybe 2 - 3 m² of the job.

Two failures are easily explained. In one, the metal hose connection to the bag developed a leak after the pressure got down to ~-0.8 bar, thus pressure was lost. The second was the result of a split in the bag, caused by (I think) a sharp edge, again causing loss of pressure. In both cases, if I'd perhaps stood over the bag for the approximate two hours whilst the adhesive cured, or been working nearby when both incidents happened I might have spotted the problem and been able to quickly rectify it. Of course, that isn't how you work, and once the job was under pressure I went off to another building where I was cutting and matching veneers for the next pressing just leaving the bag to do its thing.

The third failure is a mystery. It occurred with one of the pilasters, the ones with the large 2.5 m+ long ovolo (arc) profile. Pressure was good at both beginning and end of the pressing, but the piece came out with wrinkles in the veneer. My best guess is the vacuum didn't form correctly across the whole surface of the pressing, but was somehow localised near the extraction hose, or perhaps there was some sort of contamination I couldn't see on the MDF pilaster.

Still, every failure meant stripping and redoing. Failures of this and other types are the main reason I like to be sure there is at least 10 - 15 percent more square footage or metreage of veneer available than is actually needed, and twenty percent extra is even better: veneer is cheap compared to labour, relatively speaking, and extra leaves of veneer from the same flitch aren't always available if you have to go back to your veneer merchant for more. This, of course, matters especially if you're working on a tall and long run of matching panels, as I was in this case. Therefore, it's usually prudent to have some spare to hand to deal with contingencies. Slainte.

Re: yes tell us more

Dick Coers

You don't let the pump run on automatic during the entire pressing? Hearing long cycle times would tell you about the leak right away. I always use a melamine panel for clamping over the sandwich to distribute the pressure over the veneer. I've never seen a wrinkle stay under that.

Re: yes tell us more

Sgian Dubh

Dick,in the set up I was using the pump runs continuously, so no cycling. One of the failures occurred during an overnight pressing with the pump therefore running all night. Overnight pressing happened several times on this job. As I said earlier, once the pressing was under way I wasn't in the same room as the vac bag, so I wouldn't have heard anything to tell me there was a problem, even if the pump was a recycling type. I did have to pop into the pressing room very occasionally during a pressing, but it was rare. Mostly it was a case of start the pressing, check for pressure, make sure everything looked okay, and go away to work on another part of the job to try and get four pressing done per day.

Like you, I use a cover board on flat panels (but not usually on curved parts) which, if it's MFC or similar has shallow grooves cut in the top face just under the membrane to help air evacuate, plus pieces of breather fabric, with at least one piece positioned under the metal bag/hose connector. Sometimes I use other material for cover boards, such as a piece of MDF, and if that's the case, after softening edges, I might spray polish the board for multiple pressings of panels the same size, or for a one-off I usually simply tape some plastic sheeting to the face that's going to be pressed against the veneer.

Depending on the size of the piece being veneered, sometimes one face at a time gets pressed, and at other times both faces of the ground are pressed at the same time using two cover boards, one below, and one above.

Still, there's always the possibility of a rare failure, and I've been around veneering tasks for long enough to know it's a mistake not to build in a little time and materials for a veneering job to allow for such contingencies, especially large ones, ha ha. Slainte.

Re: yes tell us more

Bill Tindall, E.Tn.

Thank you for the detailed response.

Heat applied

CJ in MPLS

I applied heat using an iron earlier and then clamped the panel up. I am dubious about this actually working. The one thing that does seem to have happened is that the adhesive did seem to loosen, so I am of the opinion that heat will help remove the veneer if nothing else.

Re: Heat applied

Sgian Dubh

If you do end up having to remove the veneer, you could do as I do (or did in my recent work) assuming we're talking of a flat panel: I simply got at it with a belt sander and 60 grit paper, then followed up with finer 120 grit belts and a little to finish with a random orbital sander, again 120 grit. If you're feeling particularly aggressive, you could start with 40 grit on a belt sander, and work up to 120 grit through 80 grit. The belts tend to clog when you hit the glue, but you can clean the belt with one of those latex rubber belt cleaners, or just put on a new belt.

If you're lucky, it won't come to this and your repair efforts will have done the trick. Slainte.

Sussed . . . I think

CJ in MPLS

Richard, thanks.

I've done some additional panels and while the method was unscientific in that I changed more than one variable, I have had success. First, I don't think I had keyed the mdf sufficiently and so I dug out the toothing plane and had at it. Second, I used a bit more glue. And third, I reworked my pressing situation to get more and more even clamping force applied (no vacuum equipment as yet). I don't know what combination of the three was at fault, but it feels good to see a way forward.

I'll strip off the thin veneer that failed and redo that.

Thanks again for the advice.

CJ

Re: Sussed . . . I think

Sgian Dubh

In the old days, prior to vac-bags, presses, and the like, a common pressing technique was to make up cauls for the job. Basically a series of something like pine, oak, beech, or whatever 3 X 1s or 2 X1s planed true, then one edge planed to a gentle convex curve to create bearers. Following this these pieces were attached evenly spaced (~every 6 - 8") and convex edge to a thin piece of plywood or similar (6 - 9 mm thick MDF for example) to create the caul. Cauls are sized to match the panel(s). Anyway, slather on the the adhesive to the ground, place the veneer, add a sheet of thin plastic (or apply a finish to the caul) and put the caul over the plastic, and apply a clamp at each end of each bearer, generally starting at the mid-point and working out to both ends.

I haven't used the method for maybe three or more decades, but I/we used it several times in the 70s and early eighties - we didn't have a press to start with. When done with hot hide glue we warmed both the ground and the caul prior to gluing up and applying the pressure. It worked pretty well, and if done with hide glue rather than, say, PVA or urea formaldehyde types, any bubbles and wrinkles were relatively easy to deal with using heat from an iron, a damp cloth, a sharp knife, and a veneer hammer. Slainte.