Piano Finish Touch-up and Repair

Early piano finishes were varnish and shellac.  Next came lacquer, another relatively soft finish that can be affected by solvents such as lacquer thinner.  In the 1960’s polyester and polyurethane were introduced into the piano world.  These are very hard catalyzed finishes that are more durable than lacquer.  Polyester is finished to a high gloss shine.  Polyurethane is generally a satin finish.  The satin finish is achieved by wooling the surface with steel wool or 3M Scotchbrite pads.  The second way a satin finish is produced on polyurethane is what is called an “off-the-gun” method that is sprayed at the factory instead of wooled.  This is the most difficult finish to touch-up but can generally be accomplished by filling with polyester and top coating with special satin sprays.

The term “piano finish” refers to a smooth glassy surface where the grain has been filled.  Some oak piano finishes are left with an open grain finish.  

This is a mirror-like high-gloss finish that is hard and durable.  It is usually fairly thick compared to lacquer finishes.  The higher end pianos have a much thicker finish than lower end ones, making it easier for damage to be repaired.

Damage:  When polyester high gloss finishes are damaged, the repair process includes prepping the damage, filling a void if the damage is deep, adding color to the bottom of the repaired area, and pouring catalyzed liquid polyester onto the site.  If the area is on a vertical surface, a clear acetate pouch is created to hold the liquid in place while it cures (1 to 24 hours, depending on the type of polyester required).  Then the repair is sanded smooth in progressive steps from 220 through 2500 grit.  Next a buffing wheel with rouge starts returning the shine.  The finishing step uses a foam pad with polishing liquid to return it to a high gloss.

Sometimes it is not possible to get a good result pouring into a vertical pouch.  In these situations the piano must be repositioned by piano movers to allow the pouring to be done to a horizontal surface.  

Scratches:  When light to moderate scratches are the issue, they can be sanded out, buffed and polished back to a high gloss shine.  If they are deep enough for your fingernail to drop into it, they will probably have to be prepped and poured, then sanded, buffed and polished.  Years of general use can create a myriad of tiny scratches that create a dull appearance.  The piano can be buffed out to bring the original shiny luster back.