The use of Dust & Dirt Hardener is an efficient method of preparing footprints and tire tracks found in loose or sandy soil. The 638CA features a quickdrying, clear acrylic formula that adds superior strength to impressions ” lessening the chance of detail damage due to the weight of the casting material. Use it with Plaster-of-Paris, HARDCORE, or Shake-N-Cast materials. One 15 oz. (425g) aerosol can is enough to make up to 30 full-size adult shoe impression applications.