Waterproofing Works at the Flat Roof Top by admin | Jul 13, 2015 | Liquid Applied Waterproofing, waterproofing system | 0 comments Problems: Cement screed and slab cracks, water leak to the below. Solutions: Koster 21 Waterproofing Systems 1. To expose the cracks 2. Clean the surface 3. Patch all the cracks and leveled the ponded area 4.Prepare the waterproofing material 5.Work Done!