Waterproofing on “Mother Slab vs Slope Screed”

Waterproofing(WP) can be done on mother slab or on slope screed. In this article we shall compare these two methods.

Waterproofing on mother slab

Waterproofing on slope screed

 Step by step procedure:

On mother slab:

1. Preparatory works – Ponding test, Haunching, Bore packing, Pressure grouting, V-Groove packing

2. Surface Preparation – Removal of unwanted materials, dead mortar & other loose particles; Surface should be undulation free and should have a suitable moisture condition of selected Waterproofing material

3. Waterproofing Application with final ponding test

4. Protection with SBR admix and gliding layer

On slope screed:

1. Preparatory works – Ponding test, Haunching, Bore packing, Pressure grouting, V-Groove packing

2. Slope screed – slope screed with concrete or mortar with SBR admix

3. Surface Preparation – Removal of unwanted materials, dead mortar & other loose particles; Surface should be undulation free and should have a suitable moisture condition of selected Waterproofing material

4. Waterproofing Application with final ponding test

5. Protection with SBR admix and gliding layer

Comparison

 The above table shows the comparison between these two methods.

Waterproofing on mother slab can be done with basic cement based brush applied materials and has lesser work steps than WP on slope screed. Since the mother slabs are concreted without any slopes and always have some undulations, water can get trapped in filling layers and will not drain away.

Waterproofing on slope screed has to be done only with the materials that are having high elongation & crack bridging properties – e.g: Bitumen sheet, Synthetic rubber based system, high polymer/acrylic based materials. The chances of screeds getting cracked is higher than mother slab; so the screed should be allowed to cure and get cracked before doing waterproofing.

Though the waterproofing on mother slab seems to be having some advantage, waterproofing on slope screed has higher protection.