Polyurethane Waterproofing of Roof Slab
Polyurethane waterproofing of roof slab consists of two pack clear/pigmented Aliphatic Polyurethane using Polyether Polyols with Iso-cynorate for rendering flame resistant characteristic. The two pack system consisting of pigment and the solvent (Xylene/Toulene, no filter) is mixed in definite ratio by weight strictly as per manufacturers specification for preparing the coating for application. The coating will have physical features like high resistance to impact, abrasion and cracking, superior tensile strength (80 Kg/cm2 after 4 weeks at ambient temperature) and perfectly smooth, dust free glossy finish retained at least upto 3 years. It should also be resistant to acid, alkalies and have a very low water absorption rate (0.5% maximum at ambient temperature after 7 days).
1. Preparation of Surface
The roof surface is thoroughly cleaned with a wire brush and all foreign matter etc. is removed. Well defined cracks on the surface is cut to "V section, cleaned and filled up with a paste of 2 component Polyurethane based crack filling compound and white cement in a ratio of 1:2.
2. Primer Coat
It consists of two pack Polyurethane. Primer coat is mixed in the ratio as per Manufacturers’ specification. A single coat of this primer is applied by brush over the prepared bed as an adhesion coat.
The primer is then allowed to dry for a minimum of 8 hours time before the successive finishing coats of PU are applied.
3. Finishing Coat:
- The finishing coats consists of three successive pigmented sealing coats each of two pack Polyurethane mixed in the ratio as per manufacturer’s specification.
- Application of finishing coat is done with brush to a smooth and even finish. The overall dry film thickness should be 450 microns or minimum covering capacity should be 160 gms/m2 per coat.
- Each coat is allowed to dry for minimum 12 hours before applying next coat. Care is taken for quick application after mixing the two pack primer in view of short pot life of the mix and should be fully consumed within the stipulated period as per manufacturer’s specification (maximum 60 minutes at 30 deg. C).
- The PUS coating should be continued up the parapets/walls for a minimum of 150 mm over the finished roof surface. It should be continued into rain water pipes by at least 100 mm.
- The final coat of PU when tacky is sprinkled with 300 micron layer of clean sand.
- Plain cement concrete (1:2:4) of 25 mm minimum thickness with 24 SWG chicken wire mesh is laid to slope in panels of maximum 1.2 M x 1.2 M size over this. The joints between panels should be raked out neatly (after stipulated curing period) to a minimum 6 mm x 6 mm V-groove and filled up with an approved quality elastomeric compound sealant.
- Drain outlet is provided for all spouts/rain eater pipes by suitable rounding, filling and sloping of PCC as per drawing.
- At the junction of the roof and parapet or any other vertical surfaces, a fillet of 75 mm radius should be formed in cement concrete (1:2:4).