Abstract: An improved, water based, undercoating composition, primarily designed for undercoating of vehicles to prevent corrosion. It is a butadiene-styrene based polymer latex composition which contains from about 5% to about 20% by weight of mica as a filler and flattener which provides an effective moisture barrier and also functions to prevent premature gelling of the composition in combination with a sufficient amount of ammonium hydroxide to provide a composition pH within the range of 7.5 to 10.0 and, in addition, to provide enhancement of anti-foaming properties of the composition. The balance comprises small but effective amounts of minors such as a wetting agent, a defoaming agent, a dispersing agent, pigment, viscosity modifiers, and water. Also, disclosed is a solvent based, stryene butadiene coating.