According to Bob Flexner, in his book Understanding Wood Finishing, sanding sealer is merely a finish with mineral soap added to make sanding easier - the soap keeps the sandpaper from clogging up. It also tends to cure faster, so that you don't have to wait as long before recoating. It does no better at sealing the wood than a finish without the soap, and actually keeps the second coat from adhering as well. It's used in factory settings where they are willing to sacrifice some quality for speed. The name is unfortunate, as it leads people to believe that this is the best product to use for sealing. But the fact is: all finishes are sealers. CB.