SIKA SURFACE RETARDER Sika Rugasol-S is a green, water-soluble, water-thin, non-flammable liquid used on freshly placed concrete. It retards the set of surface mortar to expose aggregate. Rugasol provides a rough bonding surface for construction joints or mortar toppings or for exposing aggregate on slabs for a decorative architectural effect. Sprayed on as soon as concrete is screeded.