Extrernal wall & windows cracks repair and waterproofing works by admin | Jul 13, 2015 | Liquid Applied Waterproofing, waterproofing system | 0 comments 1. Problems: External wall and window cracks causing water leak into the building at the round building area 2. Solutions: Koster 21 Waterproofing System 1. Surface Preparation 2. Repair all the joints 3.Clean all the debris and dirt 4.Applying the Koster 21 Waterproofing System 5. Work Done!