It’s fairly common to come across a chipped key or two in fieldwork, especially where there are multiple children playing around the piano. Yamaha and Kawai sell complete keytop sets that are great to keep on hand as an additional service to offer your clients. When possible, always use a new keytop from the manufacturer to ensure the best match possible. This article is limited to the replacement of one or two keytops; Replacing a complete set of keytops requires different skills and tools.
Knife or razor blade
Large and small files
Remove the offending key from the piano and heat the keytop with a heat gun. Be sure to keep the heatgun moving to heat the keytop evenly and avoid a flame. Heat for 30 seconds and test the keytop often by inserting a razor blade or knife at the back and watching for the keytop to peel up.
Using a knife or razor blade between the top of the keystick, begin working the keytop off starting at the back of the key. If you’ve heated the keytop correctly, it should almost peel off. Do not use a chisel for this! Chisels cause damage to the keytop by digging into the surface of the wood.
Coat the underside of the new keytop and the keystick top in an even, thin layer of contact cement. Contact cement is made of polymers that seek the same polymers to form a bond. Applying contact cement to only one surface will yield a weak bond. Do not use rubber cement! Rubber cement is made to be easily removed and is spongy when “dry.” Using this glue on a keytop is asking for a callback the first time a heavy player lands a bit too hard.
Allow the glue to dry slightly (follow the contact cement instructions; dry time is usually less than 15 minutes) before applying the keytop to the key. Once the glue is tacky (should be a similar consistency of a yellow sticky note, return the keystick to the piano before you apply the keytop to the tacky surface of the key. Align the keytop with the front edge of its neighbors so the overhang, sides, and sharp cut out all line up.
Remove the key from the piano and press the now-bonded keytop firmly in your hands to further cement the bond. Allow the bond another minute to cure. Using a file, file the sides of the keytop flush with the edges of the key, looking to create a uniform keytop with the rest of the piano. Be sure to install the key back in the piano and file the edge adjoining the black key for clearance and consistency with its neighbors.
When you are finished, the key should look original and consistent with the rest of the keys.
Watch a video demonstration: