Correct rendering of high-porosity substrates (aerated concrete and lime sandstones)
Simple & safe to the goal
1. Check the porosity of underlay render, eventually pre-wet; also check if load-bearing.
2. Apply a lightweight lime or lime-cement fiber-reinforced underlay render, for ex. weber.dur 137 in 2 layers. After the first stiffening, strike off the last third of the material quantity "wet-in-wet", so that a total layer thickness of 15 - 20 mm (depending on the type of overlay render) is reached. Roughen or comb horizontally the surface. In case of openings, the embedment of a diagonal meshcloth like weber.therm 310 (woven mesh) cut to size or weber.therm 315 (arrow-shaped glass-fiber meshcloth) for reinforcing the angles is recommended.