Discontinuities in the substrate e.g. protuberances, hollows, corners, cracks, etc., lead to localised increases in the stresses imposed on fully-adhered membranes. Over time, this leads to accelerated fatigue and shortened service life of the membrane. Therefore, substrate preparation measures must be aimed at either removing these discontinuities (e.g. grinding to remove protrusions, filling hollow spots, and removing and patching broken parts) or mitigating their effects (such as rounding all corners to eliminate sharp angles).

With regard to cracks, waterproofing materials with elastic behaviour - measured in terms of dynamic crack-bridging capability as tested to recognised standards - perform better than non-elastics.

Nevertheless, good practice dictates that substrate preparations for installation of waterproofing membranes must include crack repairs. Since cracks are common, especially in large roof slabs, the question may be asked: must all cracks be repaired? 

To answer this, if we use the Eurocode 2 Standard - EN 1992-3 - as a guide, Section 7.3.1. states that, for Water Tightness Class 1*, any crack which can be expected to pass through the full thickness of the section should be limited to 0.2 mm where the hydraulic head is minimal. Therefore, all cracks of 0.2 mm width and bigger should be sealed.

(* - Leakage to be limited to a small amount. Some surface staining or damp patches acceptable.)

In the same section of EN 1992-3, for Tightness Class 3 where no leakage is permitted, liners (e.g. waterproofing membranes) are recommended to ensure watertightness.