Thread: Box lid DISASTER.

Just guessing really, but I'm thinking that when using epoxy for boat building the method I used to clean epoxy off brushes was to soak in vinegar, then wash with soap and water. The vinegar softened the epoxy, even if it was partially set. Citric acid is a mild acid like vinegar, so maybe it penetrated the veneer through the join line, softening the epoxy nearby, which lost its grip. Once the veneer was freed from the substrate it swelled with the water, giving you the humpy bit around the join.

I'm thinking the epoxy was not as set as you thought it was when you removed it from the press - it can be hard to tell if it's fully obscured by the veneer.

It never ceases to amaze me how many ways there are to fail with veneer.

Hi Dengy

1. it looks like there was glue residue from the blue painters tape on the underside of the veneer. How long was the blue painters tape in place, and was it 3M, or a no-name brand? I've never used techniglue epoxy so can't comment on the adhesive. (one of the PVAs has to date worked fine for me.)

2. Veneer tape uses a water based gum. A small amount of clean water should have been all that was required to remove any glue residue. Is Oomp designed (sold) to remove petroleum based adhesives as used on sticky labels?

3. water near MDF is usually a bad idea



I'm not sure burning MDF is such a good idea.

Thanks for your insight Arron.

I'm thinking the epoxy was not as set as you thought it was

I think that is spot on. One one of the edges where it lifted, you could see the epoxy as a fine sticky spiders web between the substrate and the lifted veneer.

My wife summed it up nicely: " Impatience, thy name is Joe" ( That's me)

She had a vested interest in this too, as she is my offsider with the veneer edge jointing and gluing

Thanks for your comments ian, the blue painters tape was only on the veneer for about 20 minutes. It all came off just prior to gluing the veneers to the substrate.

Very observant with the tape ian, but it is deceiving. It is actually a bit of paper towel left from where I was drying the board down. The blue marks you can see are the pen marks used to mark the edge of the board so that I can keep the veneers in order after re-sawing.

I have found Oomph ideal for removing gummed stickers off glass and melamine, never used it on bare timber before and was a bit worried about any possible discolouration of the board.

Previously I had trouble with the gummed residue of veneer tape showing after the tape is removed, it doesn't wash out easily, so I sanded it. I should have just waited with this board and sanded it tomorrow

Originally Posted by Dengue

I have found Oomph ideal for removing gummed stickers off glass and melamine, never used it on bare timber before and was a bit worried about any possible discolouration of the board.

straight out of school I got myself a job in Norton's Sydney factory making the glues used for sticky tape, sticky labels, contact adhesive, the sealing goo used with phone cables (and I forget the other types). The basic ingredients for each type of glue were Benzene, Tolulene, other petroleum distilates, and natural rubber. The same sorts of glue are still used for sticky labels. Veneer tape uses a water soluble glue.

I reckon the use of water near unsealed MDF was the problem. imagine trying to glue something to a soggy weetbix. or....imagine what will happen to a properly glued joint between a dry weetbix and timber, and then soaking that weetbix. if your lucky you might have a layer of weetbix stuck to the timber where the glue had penetrated and sealed the weetbix, but the unsealed/glued portion of the weetbix will just pull away.

if you can, try looking up inside the areas which pulled away, I think you may find a layer of MDF adhered to the underside of the timber. The reason why it had any force available to pull away from the surface is because it is clear you allowed alot of water to penetrate the endgrains of the thickish veneers will cause them to swell and expand.

We all know that when timber absorbs water it swells. But, what we do not realise is just how much force that can exert. I have seen house walls pushed out of alignment when a parquet floor got wet and it also rose off the floor shearing the adhesive! Your veneer swelled - so it had to go somewhere. There are always lines or areas of weakness that will fail given enough force.

The possible good news is that if you dry that veneer well enough it should lay down again. You may have to inject some adhesive under it to keep it flat after you press it. A heat gun will help the drying. You may have to knife through the bent up section and relay it but hopefully not.

For the future you might like to consider different substrates and adhesives. If the veneer is precious I use hide glue - because it is reversible so you could just lift it and go again. I have found that perfect for repairing antique veneers.

If I am making a modern item like a box lid or box base and have plenty of the veneer I veneer onto marine plywood (so water-resistant stuff). I use Purbond polyurethane in a very thin layer then wrap the veneer and substrate in freezer wrap (the adhesive does not stick to it) before using a vacuum press. I have not yet had a failure.

Dengue,

In a previous life (previous hobby actually) I was heavily involved in the Gliding movement, and held the necessary qualifications to major repairs on wooden gliders and sailplanes. I'm not sure what the current favourite glues are for wooden aircraft, but back in the 1980s and early 1990s, Techniglue was a favourite.

I suspect that your veneering glue failure is likely due to inadequately mixed epoxy, and/or incorrect proportions of the two parts of the Techniglue mix (epoxy and hardener). Too little hardener and not all of the resin molecules will react with the hardener,and the mix will result in poor adhesion and slow curing - or may never cure. The mix may eventually cure, but the strength and quality of the resultant glue joint will be questionable. If there is too much hardener in the mix, the mix is unlikely to ever cure. With Techniglue, my experience is that accurate measurement of the two glue parts is essential, as there is little tolerance on the glue mixing ratios. If you go outside of the undocumented tolerance on the mixing ratios for Techniglue (or any epoxy for that matter), you will encounter the type of glue joint failure that you've encountered on your veneering job.

In the early days of my experience using Techniglue Epoxies on wooden aircraft repairs, I had a couple of glue joint failures. Fortunately, the glue failures were discovered by myself at a latter time during the repair process, and not by a pilot while the aircraft was flying. When I had those two glue joint failures, I was using the plastic measuring spoons that used to be supplied with each batch of Techniglue. (I'm not sure that those spoons are still supplied with modern Techniglue ?)

Anyway, after those glue failures, I adopted what I later learnt to be best practice procedures when it came to doing any glue job using epoxy glues, or any other glue that requires the mixing of two or more parts.

The best practice procedures are pretty straight forward, and there's next to no effort required to incorporate them in your work:

• Make sure that you are using the Techniglue within the manufacturer's stated temperature limits. In FNQ, you won't need to worry about the lower temperature limits, but you may encounter problems in FNQ if you exceed the upper temperature limits.
• For best accuracy, weigh your resin and your hardener. Measuring some liquid epoxies (e.g. West Systems) by volume is plenty accurate, but with Techniglue being in a paste form, weighing the two parts gives a much more accurate result.
• Mix thoroughly. Be sure to scrape all the material from the surface of the mixing container to ensure that you've mixed in all of the material you've measured out.
• Leave a little of the mixed glue in the mixing cup. Check that left-over glue to ensure that it has cured correctly in the time specified by the glue manufacturer. If it's curing slowly, at the time and temperature specified by the manufacturer, you have a suspect glue joint.

In the aviation world, there were additional procedures that were used to quality control the glue-up process, but those other procedures are definitely an over-kill for the sort of woodworking that most of us are doing.

[Edit] Just a last thought - other people in this thread have mentioned that hide glue might be a better choice for veneering, due to it's reversibility. I definitely agree. One concern that comes to my mind with regard to using Techniglue (or for that matter any epoxy) for veneering is that unless you're using very thick veneers, you may get some epoxy bleeding through the pores of the veneer, adversely impacting the appearance of the veneer, and possibly adversely impacting whatever finish you choose for the veneer.

I hope that information helps.

Regards,

RoyG

Blame the tools.

Hi Roy, I think you have hit the nail on the head as to why the veneer and substrate separated once water got in the end grain of the veneer and swelled. Something had to give, and it was the glue joint. None of the MDF came away, indicating a poor glue joint, as you point out.

My approach to Techniglue has been "she'll be right, looks the right colour after mixing". You have to apply your own spoons these days, so I use 3 disposable plastic ones. Interesting how you weigh the gel, will give that a go next time.

Good point too about leaving some to dry, and testing later.

My approach to bleed through is to use the thicker shop made veneers ( 1.5 -2mm) and then sand them down on the drum sander after they have been glues to each side of the substrate, watching for any appearance of bleed through with each pass

Hey WoodPixel, this whole thing has occurred as a result of my impatient and somewhat stupid actions using water on the board, and a weak joint because I was not accurate enough in mixing the two part Techniglue in the right proportions. It takes 12 hours max to cure, I had left it for 24 hours, yet it pulled away without taking any MDF with it, indicating a poor glue joint.

Lesson learnt, thanks to everyone above is to treat the Techniglue with more respect and measure out the amounts accurately, and to never use water on veneer end grain.

My apologies to ian, there WAS blue painters tape between the veneer and the substrate. So the comedy of errors grows exponentially In the rush and panic of the glue-up, I forgot to remove the painters tape used during the edge jointing of the bookmarked veneer sheets, on one side of the board.

There were 6 x 40mm wide strips of painters tape across that joint, and the Techniglue was still in a soft, sticky gel form on the tape, ( as seen in the first pic below) but the glue was quite hard on the adjacent MDF substrate and veneer, where it took a bit of effort to separate them. But it should have been stronger, I think, and some of the MDF should have come away with the veneer if the glue had been mixed to the exact proportions.

SO EMBARRASSED !!

As my dear wife pointed out, between my sobs of despair, it was lucky this happened when I added water to the veneer end grain and exposed the problem, because in time the veneer would have lifted from the six strips of tape, much to my dismay.

Still, this was just my 2nd attempt at veneering with bookcased veneers, lots learnt

omg, Woodpixel was correct. it was the tools! wouldn't be the first time that tools have cut timber short, not cut enough, cut at the wrong angle, planed down to the wrong thickness etc. I think I will go outside and kill a tool so that the rest of them might learn!

Yes, definitely a case of the tools.

My BIL is a mechanic. He blames all car crashes on a technical failure. "It's always the nut behind the wheel".

I enjoyed this thread. Veneering is like origami or drawing. How often have they said --> to make the swan you fold in half and then half and pop! There is your swan.... seemingly missing 36 steps in between.

Ive watched 100 videos and even had a great many goes. My thoughts were that you were being too exotic Perhaps just use TB2 and a brayer/roller from Eckersleys.... seems to work every time

Its good to see this. Shows me not just what to do, but what to avoid (far more important).