500 Limestone Prewash is an alkaline-based, liquid cleaning solution used to remove carbon, dirt and other atmospheric stains from soiled and dirty limestone surfaces. 500 Limestone Prewash is designed to work in conjunction with 500 Limestone Afterwash. 500 Limestone Afterwash is a concentrated acidic cleaner formulated for use with 500 Limestone Prewash. 500 Limestone Afterwash will neutralize and remove any traces of 500 Limestone Prewash left behind after rinsing and brighten the surface. 500 Limestone Prewash and Afterwash do not contain abrasives or harmful ingredients. The limestone is cleaned without damage or alteration to the natural appearance.