I got a amish made kitchen table a couple years ago. The finish is resistovar varnish ( a valspar product?). Over time white areas have developed on the surface of the table. Is this due to moisture or heat? These white areas sand out with very fine sandpaper. I would like to lightly sand the entire table surface and put another coat of varnish on it. There is nothing called resistovar varnish on the shelves of the home improvement stores. Could I use another type of varnish, spar varnish or perhaps polyurethane?

Thanks

Missy