55-50 Eco-Mastic is a water based mastic for weatherproofing and protecting thermal insulations on equipment, vessels, piping and fittings. It dries to a tough flexible, fire and chemical resistive finish that is easily cleaned. 55-50 Eco-Mastic can be used with fiberglass, mineral wool, polyurethane, polystyrene, cellular glass, calcium silicate, and foam glass insulation.