Frequently Asked Questions

How is Dekguard PU different from a cementitious waterproofing coating such as Brushbond RF for a rooftop terrace?

Cementitious waterproofing coatings such as Brushbond RF are rigid or semi-flexible cement-based coatings that provide good waterproofing on rooftop terraces and concrete slabs when the substrate is stable and crack movement is limited. The key limitation of cementitious waterproofing is its limited flexibility — crack bridging ability is typically up to 0.3 to 0.5 mm for the best flexible cementitious coatings. When a rooftop slab experiences thermal movement between summer and winter (which is large in Indian conditions with ambient temperature swings from 5 degrees in winter to 48 degrees in summer), the slab moves significantly — new cracks form or existing cracks open beyond the bridging capability of a rigid coating. Dekguard PU, with elongation of 200 to 400 per cent, can bridge crack movements of 1 mm or more without rupturing, making it a more robust choice for exposed rooftops with significant seasonal thermal movement. Polyurethane is also more UV-resistant than cementitious coatings in direct sunlight exposure. The trade-off is cost — polyurethane waterproofing is more expensive per square metre than cementitious, and application requires careful surface preparation and experienced applicators.

Can Dekguard PU be applied directly to a concrete roof slab without primer?

A primer coat is recommended before applying Dekguard PU on concrete substrates to ensure maximum adhesion and eliminate pinholes caused by air escaping from the pores of the concrete through the wet polyurethane film as it cures. Unprimmed concrete surfaces have open pores that allow air to escape during coating application and early curing, producing pinholes and holidays in the finished membrane that represent waterproofing defects. Applying a primer (typically a penetrating polyurethane or epoxy primer recommended in the Dekguard PU data sheet) before the coating fills and seals the surface pores, preventing pinhole formation and providing a chemically receptive surface for the polyurethane topcoat. The primer must be applied at the recommended coverage rate to achieve full pore penetration, and the Dekguard PU coating must be applied while the primer is still within the overcoating window (before it has fully cured through).

How many coats of Dekguard PU are required and what is the typical coverage rate per coat?

A minimum of two coats of Dekguard PU are required to build up the specified waterproof membrane thickness, with the second coat applied at right angles to the first (cross-coat application) to ensure full coverage without holidays or thin spots from the roller texture. Three coats are recommended where the highest reliability is required or where the substrate has surface irregularities that increase pinhole risk. The typical coverage rate per coat is approximately 0.5 to 0.8 kg per square metre per coat depending on the surface texture and the specified film thickness — a total dry film thickness of 1.0 to 1.5 mm for rooftop waterproofing requires approximately 1.5 to 2.5 kg per square metre of Dekguard PU total across all coats. High points and ridges in the substrate consume less material and low points consume more, so the average coverage must ensure that no areas are below the minimum film thickness. Strip holiday testing using a low-voltage wet sponge holiday detector on the finished membrane is recommended for quality assurance on critical projects.