I recently sand blasted the underside of a 1960 Pontiac Bonneville and found no trace of red oxide primer which I thought to be the standard underbody floor color. The car did appear to have factory undercoating as the undercoating was thick on the body but not on the frame. The only color we could find under the undercoating appeared black with more white prevalent towards the outer area (car is white so this is likely overspray). Can anyone confirm if red oxide would be correct and if GM did something different on factory undercoated cars?