Golden Acrylic Medium : SANDABLE HARD GESSO 236ml can only be used on rigid surfaces such as wood. Golden Sandable Hard Gesso is formulated with 100% acrylic polymer emulsion. It contains high levels of titanium dioxide, calcium carbonate and talc to produce a sandable surface which is smoother and more even than one created using regular gesso. NOTE: This product is designed for rigid substrates only (such as hardboard, wood or metal panels) and is NOT to be used on flexible materials, as cracking may occur.Only apply to surfaces prepared with one or more coats of regular gesso. Apply in multiple thin layers, gradually building up to the desired thickness. A single thick layer tends to crack upon drying. Allow to dry completely before sanding. Cured acrylic films are easier to sand. Start with coarser grit sandpapers, followed by subsequently finer grits until desired smoothness is achieved.