Opening the soundbox for major repairs

  This project is good illustration of why it is sometimes just better to pull the back off an instrument to make repairs rather than work through the soundhole. Our project is a late 80’s Guild D-30 with a Maple body and laminated Maple neck. The guys who play these older Guilds are very dedicated to them and often will do what it takes to keep them playing.

  So here is our current situation. This guitar was crushed pretty badly at one point. It looks as if it was stepped on. Someone has already made some repairs some time ago and actually did a really good job of getting the top back together. The problem is the repairs were never really finished. The guitar came in strung and strumming with a saddle that was way too high for comfort, over ¼” above the bridge! Not the usual situation for an old acoustic where the neck needs re-set. It was obvious that the top was still caved in.

  A quick look around showed the bridge was lifting, both sides of the X-brace were broken, some finger braces were missing & none of the crack repairs had been cleated. If this old guitar was going to keep playing it needed some real work. I very quickly decided it was best to simply open up the soundbox so all the damage could be clearly seen and easily repaired. So the first step was to remove the bridge. I used my heat shields made of cardboard and foil, heat gun and spatula. As always I like to work from side to side with my spatula completely under the bridge as it makes for cleaner removal. I can see once it is off it was re-glued before.

Next I need to remove the back binding. This is done carefully with my heat gun and a small spatula. Heating a section and working it loose and then holding the section in position with some blue tape behind me as I go. If you do not keep the binding close to the body as you remove it the soft, warm plastic will cool in a shape other than what it should be to fit back on nicely when I put it back together. Once the binding is loose and has cooled so it retains shape it can be put aside.

Now I can remove the back. The joint is still warm from pulling the binding so it doesn’t take a lot more from the heat gun to get it going. I start at the waist from inside the box with my thin spatula. This helps prevent splitting the lining and pulling large parts of it off with the back. I use a piece of wooden dowel to keep the joint open as I work and to help pop the joint loose as I work around now with my spatula outside.  As you get closer to completing the removal you must start to exercise greater care. It is really easy to split the last 6-8” of lining instead of separating the glue joint.

  Now I can start to look around and really see what there is to repair. Some of this would have been almost impossible to find with mirrors and feelers and even tougher to repair properly while the box was closed. Here we see the damage to the X-bracing and soundhole reinforcement. Also notice the broken and missing lining and loose bridgeplate.

Some of the finger braces are MIA and the tone bars were not glued back on very tightly. You can also see how broken and crushed the top was in these photos as well.

Next I will remove the bridge plate. It is in good shape but as I already noted is loose. I can also see from outside when I pulled the bridge that the top was crushed and fractured in between the bridge and the plate which will require some attention as well. So with my heat gun and spatula again I remove the bridge plate. This does not come off as clean as the bridge because the spruce it is attached to is very fractured.

Now I can start to actually make some repairs. First I must prep them so I get good solid glue joints, otherwise all this work will be for nothing a few months after the instrument is back in service. Any old glue must be cleaned out of the failed joints and oxidation cleared away so the glue can get a good purchase on the wood. In order to do this I put some 150 sticky back sandpaper on my spatula and sand the joints like so one side at a time

Now using my spatula I can start to work glue into the cracks and joints. Making sure to get the entire surfaces inside coated.

My go-bar deck is very large. I can easily fit complete instruments on it and this will make clamping everything back as it should be very easy. I use my arched cauls that I use for building my tops and start with the main breaks and loose places on the X-bracing.

Next I glue back together the shattered wood fibers under the bridge plate using a thin Plexiglas caul. And take care of the last break in the X. I also make and install replacement finger braces and take care of the rest of the loose braces in like fashion. I also place a few wood cleats on some of the longer cracks, replace the pieces of broken lining and reinstall the bridge plate.

After all that is done I reinforce a few areas with some muslin cloth soaked in glue. This is a technique I picked up from a violin repairman and it works well in certain situations adding strength but not weight. This is what the box looks like all repaired and ready to have its back put on.

Unfortunately the back will not just drop back on. The sides have sprung out of shape a bit and must be pushed back into alignment. If this is not done carefully and precisely the binding will not fit on properly and the job will look and feel very bad. This is the reason I think most shops do not go this route and opt to try and find and make these repairs through the soundhole. Here is what it looks like with the back just laying on the box.

I have a jig set up to make this job fairly quick and easy. It is comprised of a plywood base and clamps made from 5” aluminum angle. I wish I could take credit for this rig but I saw the idea on Frank Ford’s page, Thanks Frank! I have wooden cauls made with the proper offset for the binding channel. Here is a view of one of the clamps.

I also use a collapsible spreader as needed to push outward on the rims as necessary. Using the back as my guide I install clamps as needed and adjust them until I have a perfect fit. I also use a tapered wedge under the neck where it joins the body to get the neck back at the proper angle. Here is the body all jigged up and ready to have the back reinstalled.

The back is installed in my go bar deck.

Now the binding can be reapplied. First I just hold it in position with some strips of masking tape. Starting at the end graft I carefully work Ducco cement into the joint about 6” at a time with a toothpick. I want to get all the wood of the binding channel coated to get a good bond but do not want a lot of squeeze out or mess as it will be difficult to get off the lacquer I then use some packing tape to cinch the binding tight and hold it until the glue sets.

Celluloid shrinks with age. That is why bindings pop loose or crumble after many years. This is how much the back bindings have shrunken in 25 years. I fit a small piece of new binding to close it up.

Here is our back after it is all back together. All I did is a bit of buffing do clean up the work, there were no finish repairs done here. This could be made to look truly as if it was never off with a bit of time with the airbrush and buffer but this client is happy with the repair as it is.

Now I can re-set the bridge. But before I can do that I need to make some repairs to the top under it. There are two sections where the wood is either missing or to splintered for my liking so I will replace those sections. First I cut some repair plates from some scrap spruce and outline them over the areas I wish to replace. I then rout them out with my inlay router to a depth just deep enough to give a good true glue surface. The plugs are then glued in place using some magnets to clamp them.

Once these are dry they are leveled with a crane neck chisel and all the old glue scraped off to provide a good clean surface to glue the bridge to. I can then floss the bridge to fit the top using a piece of 180 sandpaper lined with tape on the back to prevent scratching. Once I am happy with the fit the bridge is glued back on and the pin holes reamed.

Here it is all fixed up. The saddle height is very good and will allow for a fair bit of adjustment as the guitar ages from here helping to put of any additional work like a neck set for quite a while. Thanks for following along and if I can ever help you with anything please feel free to contact me, Thanks.

www.brianhowardguiatrs.com