Refinishing pre-cat lacquer
In his reply to my last post, Tim Neun asked about repairing a table top finished with pre-catalyzed lacquer. This is right in keeping with my recent post subjects so here’s what I think.
If the table had been finished with conventional nitrocellulose lacquer, a fresh coat would “burn in” to the old finish. A good sanding to powder up the old finish and remove any scratches would be all that was needed to prep the surface.
Since the table was finished with catalyzed lacquer, this will not work in quite the same way. The bond between the old and new finish will be “mechanical” since the fresh material will not react in any way with the existing coating. It will be necessary to sand out any and all damage, including any chips in the finish. You are going to want to be careful here because, whatever the finish, the wood will have built up some patina and if you sand through into the wood, you will end up with blotches. At that point, the only option would be a completely strip down to raw wood and refinish.
Assuming that you are able to sand out the existing finish without cutting through it, I would sand the surface to 180 or 220 grit. I would not go finer because I would want to have some tooth to the surface for the new finish to bond to. I would be more comfortable using conventional lacquer for this because I think it would bond to the old finish better than catalyzed lacquer. But if your surface prep is good, catalyzed lacquer should bond well enough.