From RGP:
From: bogart
Subject: Re: Epoxy repairs to playfields

That certainly wouldn’t hurt, but I don’t think it’s really necessary. I
find the stuff hangs on like grim death if you prep the area properly.
Use a wood rasp or very coarse sandpaper to remove any loose, splintery
bits and make sure you’re down to solid wood. Then clean the area with
something that will remove all traces of grease, oil, and wax. I use
Naphtha, a highly refined type of paint thinner. Rub the area well with
a cloth damp with the paint thinner, soak some in. When this dries, go
for the putty. When done like this, I’ve sanded, chiseled, and drilled
the putty with no hint of any looseness.

bogart
www.pinrestore.com