Rebuilding a Mandolin Top
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   I have divided this section into two, working with wide cracks, which can not be pushed together under thumb pressure, and narrow cracks, that can be pushed together, or are very fine and show no visible gap.


Repairing Wide Splits in the Table
   Another common problem, caused by shrinkage of the braced top, is a split along the glue-line where the 2 halves of the book-matched front were glued together. Usually the top is still firmly attached to the struts beneath and cannot be forced together again.    The solution is to insert a thin sliver of spruce into the gap. Old wood is used where possible, and it is carefully pared down to the exact shape of the split, before being glued in.
I try to make the fillet wedge-shaped, difficult when thin, so that is gradually forced into the gap, which itself has slightly angled sides. It is often necessary to use a clamp to keep the pressure on while the glue sets. Once sanded, if done well, there is nothing to show that the insert is there other than a slight colour variation, which in time will even itself out as the 'new' wood darkens in the daylight.
   Here is another example, but in this one the crack is not down the centre-line, which is just visible to the right. A portion of the table has given way, in this case in 2 places, the piece in between having been lost. A similar operation, but using a much wider fillet.    Another photo of a centre-line glue-up. I often glue re-enforcers under the split, similar to the cauls visible in this shot, to try and strengthen the weakened area.


Repairing Narrow Splits in the Table
   When I have an instrument with a narrow split; one that can be pushed together easily with thumb pressure, or where the sides appear to touch; it is sufficient just to work some glue into the crack and re-enforce beneath. I have found the best glue for this, (i.e. that doesn't stain the wood and sands off fairly easily), is Cascamite. I find Titebond a bit too thick.... Smear a small amount along the line of the crack, and work into the crack by pressing each side of the crack in turn. I also run my finger along the crack whilst pressing one side to help push the glue right up against each face of the crack.

With a damp cloth, wipe off any excess glue, being careful to wet the area around the crack as little as possible. Then use a few pieces of masking tape, pulled tight across the crack to hold it together whilst the glue dries. If at all possible, fit clamps to pull the sides in and force the crack together. Finally, when the glue is dry, put a couple of small cleats across the crack underneath to re-enforce the repair.