Traditional sanding sealers were made with nitrocellulose lacquer, silica, sometimes diatomaceous earth and talc. New/current formulas have changed considerably, so one needs to read the can carefully. In So Cal, you can no longer buy sanding sealer for brushing because of air quality regs, and I have not yet figured out how to doctor the spray formulas to get good brushing characteristics. Current formulas have probably reduced or eliminated the silica content because silica is carcinogenic when airborn. That's why we in So Cal don't have much to choose from in flat paint finishes, because silica is the traditional flatting agent in paints. Good NOS sanding sealer is going for big money in the local secondary market.
