Self-levelling underlayment. 22.7 kg. FLOW-MIX is a fast-curing self-levelling mortar, which requires only the addition of water for levelling and smoothing uneven floors in a simple, practical and durable way. Suitable for levelling all kinds of exterior concrete floors and plywood surfaces exterior grade). FLOW-MIX can be applied at thickness that may vary from 3 mm (1/8 in.) to 25 mm (1 in.) in a single application. FLOW-MIX is a Portland underlayment with high performance self-levelling underlayment for (outdoor type) grade plywood and for concrete.