This article applies equally to Acoustic Guitar as it does to Classical Guitars and Ukulele’s. By the time you are ready to glue the back on your guitar you should have accomplished the following tasks:
Contoured the Sides for the Back Shape
Installed the Linings
Installed the Finished Top on the Sides Including the Rosette
Installed the Head Block
Install the Tail Block
Installed the Neck for a Classical Guitar
Installed the Side Braces
Fit the Acoustic Guitar Neck
Dry Fit the Guitar Back
Finish Sanded Entire Interior Surfaces & Braces
Carefully Fit Back To Sides & Cut Brace Ends Into Kerning
Sanded The Edges of the Side & Kerning With Arch Sander To Receive Arched Back
The reason it is important that you have accomplished all of the above operations is once you install your guitar back it is too late to do any of the above tasks without removing the back plate.
Tools and Materials:
2-Part Epoxy Glue
1″ Wide Elastic Tape
Wood Cam Clamps
If you have exotic wood species, use 2-Part Epoxy Glue to glue the back to the sides/lining. If you are using a non-resinous wood, use Titebond.
GLS Tip #1: If you haven’t already, trim the Guitar Back Plate to exact form of the sides. Place the back in place and trace the side contour on the plate. Sand the back plate to the trim line. Do this in order to prevent any cracking of the back plate when applying pressure from the 1″ Elastic Tape.
Spread the Glue:
You will only need to spread a thin layer of glue on the lining/sides of the guitar and not on the back plate. Use a small piece of wood veneer that has one straight edge and use it to spread the glue thinly over the gluing surface. Also work some glue into the brace channels, so all surfaces of the braces will be adhered to the linings and guitar sides.
Be sure not to spread the glue too thickly as you will be unable to clean glue squeeze out from the interior of the guitar very easily (although it is possible through the access hole at the soundhole of the interior form.
Start to Secure the Back Plate:
Perhaps the easiest way to start is to place a couple of Wooden Cam Clamps to apply pressure at the Head Block and Tail Block areas.
Set the back plate into position – it should pop right into place. Start to wrap your 1″ Elastic Tape with a few wrappings at the waist of the guitar. You should stretch the tape a fair amount to place downward pressure on the back plate.
Now you can use a criss-cross method on the lower bout, then the upper bout to secure to top to the sides. When done, there should not be any of the guitar back showing – it should be completely covered with tape.
Alternative Clamping Methods:
There are about as many ways that luthiers attach their top and back plates as there are guitars made. It’s not that any are completely right or wrong, it’s what works for you. Here are a few alternatives to consider:
Rubber Bands: I used this method for years. I just purchased a big bag of wide rubber bands from the stationary store. I finally abandoned this methods after being snapped one too many times with a broken rubber band. They don’t last very long either, and it isn’t as fast as the elastic tape method. They still do come in handy for dry fitting the plates to the sides and can be used for the initial clamping to hold the plate solid while preparing to use the elastic tape.
Adhesive Tape: I do use this method for adhering the binding to the guitar, but not the plates. I does work well, but again is quite a bit slower as you have to cut dozens and dozens of pieces of tape and often when you apply too much pressure, you will break it, unless you use the filiment tape which you will cuss at when you try to remove it and it tends to leave residue on the wood.
Spool Clamps: As much as I love Spool Clamps for clamping portions of guitar sides for repair purposes, it is a very agonizing ordeal to get them all adjust properly and place them around the guitar perimeter – you shouldn’t need nearly this much pressure to adhere you plates anyway. If you do, your back plate is not fit properly.
Wooden Cam Clamps: Ahh the securement of the back plate by brute force. Again, you shouldn’t need nearly this much pressure and you introduce unnessary stress to your guitar. Plus, do you have all of these camps in your shop? I don’t.
Elastic Tape: I finally discovered that by using one continuous piece of 1″ elastic tape I could easily clamp a black in record time. You simply start at the butt end of the instrument and stretch the top to clamp the plate at the heel, wrap it around the studs, shift over one stud and continue to criss-cross across the plate until the entire surface is clamped by the tape. Be sure to tie off the end well enough or the entire piece will unravel and you will have to start over.
GLS Tip #2: At about the the 25%, 50% and 75% completion points of applying the elastic tape, tie off the tape with a couple of half-hitch knots. This will prevent a complete unraveling of your work if the tape slips out of your hands. I have had this happen to me several times and the result was to start right from the beginning. I now use the half-hitches all the time.