With the amount of tension pulling on an acoustic guitar bridge, it is not uncommon for them to begin to lift off of the top.
We repair this by heating the bridge to loosen the glue and then work the bridge off the top. From there, the bridge and the top are cleaned of the old glue once done the bridge is reattached. While relatively straight forward, this is still not a good idea for the amateur repairman to attempt. There is plenty of opportunity to damage the guitar by over heating the bridge or surrounding area, tearing up the top by try to remove the bridge before the glue is softened or by being to aggressive. Bridge removal comes down to feel. Once the glue is soft, the luthier uses something like a putty knife to work under the bridge.
After the bridge is successfully removed, the area can also be more thoroughly examined. There are times the top may need a repair before the bridge is reinstalled.
From here the glue cleanup begins, and it there is any damage to the top, it will be addressed. How well the bridge repair holds is directly related to how well the surfaces are cleaned up.
Glue choice is also critical to this stage, and there are only two good choices. Number one is hide glue. When possible, hide glue is our first choice for most wood to wood repairs. A top quality wood glue is acceptable and more than likely what most repairmen would use. Hide glue is more difficult to work with, even though it does produce better results.
Aside from bridges coming loose, we see acoustic guitar bridges crack across the bridge pin holes or the ends of the saddle slot. With so many holes in a row, if the bridge is going to crack, this is the weakest area. If the crack is forming around the saddle slot, this is an indication that the saddle in place may be to loose in the saddle slot putting tension on another weak area of the bridge. When a bridge cracks, there is more opportunity for damage to the top, where a lifting bridge is usually just that. Depending on the severity of the crack, we may be able to save your stock bridge. If a crack is fresh and goes together cleanly, it can be repaired. We would want to know why it cracked though to avoid this problem from occurring again down the road.
If a bridge cannot be saved and a replacement is necessary, this can become a much more costly repair. Some pre-made generic bridges are available but often will not match a guitars original bridge. If you need (or want) a custom bridge to replicate the original, these are typically made to fit your particular guitar. Be prepared for price shock sorry but this the reality of the situation.
One other thing that comes up is bridges that need to be moved to correct intonation. Some of the world’s top makers have documented cases of bridges being installed in the wrong spot resulting in incorrect intonation (when working in a factory mistakes happen). This actually comes up a lot on certain vintages of acoustic guitars. Since the bridge pin holes need to be relocated as well and there is the finish to deal with, this is another pricey bridge repair. For higher dollar instruments it is a good investment. For lower dollar instruments, it may be a good idea to attempt to minimize the issue by relocating the saddle in the bridge. This would be done by filling the saddle slot with a piece of wood that matches the bridge and then recutting the saddle slot in the bridge. Not all guitars will be a candidate for this it will depend on the particular bridge and location of the pin holes as well.