The mineral substrate must be even, solid, load-bearing, clean, crack-free and free of substances that may impair adhesion. The surface must have a rough, open pored structure with good grip. All edges must be cut off or chamfered. Cove all corners with a hollow moulding of at least 4 cm radius. Repair any defects, screed over rock pockets and fill mortar joints, e. g. with CT 23 Repair Mortar or CN 91 Wall & Floor Repair Mortar. Enlarge the cracks and fill them with cement mortar alternatively, pressure-grout the crack with CK 740 Epoxy Resin. If the brickwork is uneven with numerous projections and defects, produce a levelling render made of cement mortar. Make sure to thoroughly prewet the prepared substrate. When waterproofing wall and foundation areas indoors or outdoors, e. g. in the case of rear penetration of moisture, pre-treat the areas with CO 81 Silicifying Fluid. When waterproofing from negative side, the substrate must have sufficient mechanical strength.