COVERAGE A 12kg bucket of STOPGAP 500 mixed with 6.75 litres of clean water will cover approximately 13.5m2 at a thickness of 1mm. STOPGAP 500 is a rapid drying floor finishing compound providing a smooth surface to plywood, existing floor smoothing underlayments, sand / cement screeds and other rigid dry absorbent surfaces, prior to the installation of floorcoverings.