Area of use
CM 780 Fast Fibre is a pumpable, self-levelling underlayment. The product is fibre reinforced, quick setting, self-drying and has a good flow rate. The CM 780 is suitable for new construction, renovation and heated floor systems. The product is intended for indoor use on substrates of concrete, lightweight concrete, stone, ceramic tiles, wood and gypsum underlay.
The substrate should be clean and free of dust, cement skin, grease and other impurities that can prevent adhesion. Adhesion and surface resistance of the substrate should be no less than 0.5 MPa. Always prime the underlying substrate with PP 600 and allow to dry before pouring. In terms of the primer forming a film, the temperature of the substrate must not fall below 10 °C. For best results, the ambient temperature in the work area should be between 10 and 25 °C. At higher or lower temperatures, the time for curing will shorten or extend. With the risk for cracks due to shrinkage or settings in the subfloor, a concrete surface should not be leveled within the first 28 days after casting. As a recommendation the RH in the concrete should have reached RH 90 % as the upper limit for pouring the CM 780. Use the Combimix form foam for edging. In order to avoid drainage pipes from getting clogged, always make sure the drains are properly sealed before pouring.
Mix the dry powder with max 3.6 liters of water (max 18 %) per 20 kg bag. Mix with a drilling machine and a whisk, or a mixing pump intended for this purpose. The correct water mixture can be tested using a slump test with a cylinder with Ø 30 mm and a height of 50 mm on 300 x 300 mm plexiglas plate. With the correct water mixture, the spread should be max 135 mm. The slump test also checks that the material is well blended and that there is no separation.