Glue for laminated sides

[Alan Peterson]

What glue would be best for molding up 3- or 5-ply sides, the way Gretsch did on its original Atkins line?

[Chuck Tweedy]

I vote epoxy.
Good open time and gap-filling.

[David King]

What about a powdered urea glue like Unibond 800? I've never tried the stuff but it seems like it would have some advantages, particularly longer open time, low moisture and crisp glue line. I'd take it over epoxy if you were also concerned about possible bleed-through, especially if you are using a vacuum press method.

[Bill Raymond]

Titebond is fine. Epoxy is a bit messy to work with and, Chuck, its gap-filling properties are not likely to be needed here, as there should be no gaps to fill! If you can work fast, hot hide glue would be good, too--or one could simply let it gel, clamp the laminae together and reheat to get the glue to bond--which would be doable but perhaps not worth the effort. I believe Ken McKay has mentioned that he has used polyurethane glue, but I'd be concerned about bleed through gluing the laminated sides to the form. Weldwood seems to hold some promise, but I've not had experience with it personally. I've used Titebond with good results.

[Clay Schaeffer]

For veneer thickness pieces I found epoxy to work the best for me. I handle "bleed through" by also pore filling with epoxy. The few times I have tried water based glues the moisture created stresses that caused some warping of the veneers. I built the sides from veneers with the grain all aligned in the same direction ,so this may have exacerbated the problem.

Bill,
What method do you use when gluing with titebond?

[Bill Raymond]

Clay, I'm not sure what you mean by "method": I simply spread the glue on and clamp the laminae. I have a male form with female cauls. There is additional room between the cauls and the form to put several additional layers of veneer over the glued laminae. This helps even the pressure out.

[Bill Raymond]

Here is a photo of my form (if I did this right).

[Craig Bumgarner]

I've been using Weldwood Plastic Resin Glue. It is a powder mixed with water, but it seems to hydrate the wood considerably less than Titebond, gets very hard in 24 hours and has a mahogany brown color that matches the wood I seem to use most of the time. I've used lots of epoxy over the years and while it is great stuff, I prefer the PRG for ease of use and clean up with water. PS, don't breath the dust while mixing, contains formaldehyde. Epoxy is not exactly benign stuff either. If I were gluing up a light colored laminate like maple, I might consider epoxy.

For laminating sides, I use the Michael Collins style mold: a female cawl 2" thick x 4" wide made from a stack of 3/4" MDF, sawn to shape, epoxy coated and waxed to prevent glue from sticking. To clamp the veneers, I use a semi-flexible matching male cawl (laminated thin plywood, about 1/4" total). Lots of clamps.

For backs, I have used two plates of MDF to sandwich the veneers and lots of clamps, but I recently made a veneer press that is faster and develops a more even pressure.

[Barry Daniels]

I have used both Unibond 800 and West Systems epoxy for laminating sides. There is not really much difference. The epoxy has more tendency to bleed through but that can be minimized by adding a thickner to the glue like chopped poly fibers. Unibond also has a thickener available to reduce bleed through. Both glues dry equally hard.

[Simon Magennis]

No personal experience. I have also heard Urea mentioned in this context. Personally I would avoid epoxy as the allergy risks would put me off and I find the smell way to overpowering for me.

[Bill Raymond]

Craig, I forgot to mention that I laminate my backs over an arched form in a vacuum bag. Maccaferri apparently wanted to laminate the backs on an arched form, but couldn't get Selmer to do it. It always seemed like a good idea to me.

[Craig Bumgarner]

Bill: So how does that work for you? What is the shape of your mold? Does the vacuum yield a fair enough laminate so don't have to do a lot of sanding on the outside surface (so you can use modern .022" veneer without breaking through). What is your veneer schedule?

I've been using a flat laminated back plate (4 layers of .022" = .088" OR 3 layers of 1/32" veneer = ~ .110") and then bending over arched braces. I used arched braces and relatively straight sides or a 15' radius sanding dish for the braces and the rims. Either works pretty well, though the full radius approach seems to come out more fair.

BUT..... I've lucky enough to have had four Castelluccias come by my shop the last couple years, just saw another this weekend and they all have laminated backs without braces. Some are arched across the body about 10'-12' radius and along the body (fore and aft) less so, sides are straight and of equal width throughout. Others have a molded archtop shape. Thicknesses run 3.8-4.5mm. The backs are fairly flexible but seem to hold their shape well enough (they are all 55-65 years old). Some Busatos have molded archtop style backs without braces or with just one little floating brace in the middle of the lower bout, not joined to the rims, to help hold the shape I suppose. Anyhow, I'd be interested in trying to do this. Vacuum over a mold would seem to be the way to do it. I have some experience with vacuum molding wood parts and have a vacuum pump.

Are your molded backs installed without braces? Any problems with warping? I had warping problems when I first started laminating backs and took this to be the result of uneven distribution of grain orientation and the swell & contract effects of glue absorption. Initially used four layers oriented 0-0-90-0 degrees with the 0-0 being the outer layer. I was also using different woods, the outer two layers being walnut, the middle being poplar and the inner most mahogany. Got a pretty strong curl across the back. Unfortunately the warp was in the wrong direction. I found if I used five layer 0-90-0-90-0 of .022" or recently, three layers 0-90-0 of 1/32" veneer, all the same species, I had less of a problem. I still, however, worry about warping on an unbraced back, sooner or later. What has your experience been?

CB

[Bill Raymond]

Craig, being somewhat old-fashioned, I don't think in terms of radius, but simply the height of the arch. I made my mold by drawing a side view of the back arch--using a thin strip of wood to draw the curve--so that I had a 7.5mm rise at the widest point of the lower bout (I used measurements that Max Debelleix had made of an Eddie Freeman Special body). Then I measured the rise at each of the brace locations and glued appropriately curved strips to a piece of plywood cut out to the shape of the guitar body. Then enlarged the piece of plywood by gluing a number of strips of wood ca. 2mm thick around the periphery which I could then plane to meet the shape of the arch, much as you would fair the linings to fit the domed plate. Finally I glued a piece of 3mm plywood over the whole thing and filled in the voids between the flat plywood and the domed plywood with spray foam. I trimmed the domed plywood piece to the enlarged body shape except that I left the waist untrimmed so the mold has the shape of a guitar without a waist.

I have been laminating rosewood exterior and African mahogany interior to a cross-grain core of 1/16 inch thick tulip poplar crossbanding. I haven't tried going braceless yet, but the dome seems to hold with minimal warping that is easily overcome when glued to the straight edged sides. As I recall, the finished lamination turns out to be about 2.45mm thick before any sanding is done.

[Tom Sommerville]

There was a company that experimented with veneer laminate backs and sides and the finish, after a time began to check due to seasonal movement. They lost a lot of money on that.

I'm still trying to figure out what went wrong, and wonder if knife-cut veneer should be avoided altogether on highly polished surfaces. One veneer dealer I spoke to suggested that the culprit may have been the choice of glue. He told me that a rigid glue line was critical. That would rule out aliphatic resin glues.

[Craig Bumgarner]

Bill: Thanks! Lots of good ideas there.

• What kind of glue do you use when you vacuum bag? I seem to remember that glues that set by internal reaction like epoxy or PRG should be used.
• Any problem with the poplar corrugating when glue is applied? I found I had about 2 minutes before it would corrugate badly, like 1/4" high over 1/2" waves. It can be hard to flatten them out. I switched to mahogany for middle layers, but this makes the laminate a little heavier.

Tom: I had checking in the FP finish on the one set of b/s I laminated with Titebond about a year after finishing. I had not considered that Titebond might have been the problem, but you might well be right. I had a strong feeling that Titebond really hydrates the wood and of course it will eventually shrink back up, though it was at least three months between laminating and finishing. Your suggestion that the lack of a rigid glue line may be part of it too makes sense too. After this one set, I switched to PRG which seems to hydrate the wood much less and gets fairly rigid. Recently, I switched to using marine spar varnish on the b/s only, to seal the wood and fill the grain before french polishing everything, including the b/s. No checking so far.

[Bill Raymond]

Craig, I've only used Titebond, but I think I would like to try the PRG sometime. I'm also trying to figure a reasonably efficient way to use hot hide glue (maybe fish glue would be easier?) The poplar does "corrugate" (nice choice of words, Craig) but seems to flatten in the vacuum bag satisfactorily. It helps to smooth out the wood by "ironing" it in the bag with your hands the vacuum is applied.

[Mark Swanson]

And what is "PRG"?

[Craig Bumgarner]

PRG = Plastic Resin Glue. A pre-mixed, pre-catalyzed urea formaldehyde glue. Comes in powder form, water added to start the reaction. Various manufacturers, DAP Weldwood is the most common I think, that is what I use. Cures hard (cured resin out of the cup will snap when bent within 24 hours), has fairly long open time, spreads nicely, is not particularly sticky to use, cleans up with water, does not hydrate the wood badly as aliphatic resin glues, can be used in vacuum clamping systems. All of which makes it good for laminating.

It has become more difficult to find but you can still get it mail order without too much trouble and usually cheaper than on a hardware shelf, assume they have it at all.

PRG has a shelf life. Weldwood says one year, the tubs are dated. Stored cool and dry, it will last longer. The in-field test is whether it will mix readily with water and make a smooth liquid. If it is difficult to combine with water or results in a grainy liquid, it is no longer good. PRG is a pre-mixed, pre-catalyzed product with everything it needs to be glue in the can except water. I think what happens is the power eventually pulls enough moisture from the air to start some curing in the container and the grains are the resulting cured glue particles.

As I have said, it has been working well for me for laminating backs and sides. I don't use it elsewhere because 1) it contains formaldehyde, 2) mixing glues for every day use is a pain and 3) for a lot of purposes, it would just not be as good as alternatives. Titebond works better for most everything else I do in the guitar world.

CB