Frequently Asked Questions

What is the difference between SikaTop 66 and SikaTop 107 Seal and when should the flexible coating be specified instead of the crystalline product for a terrace waterproofing project?

SikaTop 66 and SikaTop 107 Seal are both two-component polymer-modified cementitious waterproof coatings from Sika but have fundamentally different waterproofing mechanisms and performance characteristics. SikaTop 107 Seal is a crystalline (semi-rigid) waterproofing system — it has a lower polymer content and relies primarily on crystalline pore blocking and a reduction in concrete permeability for its waterproofing action. It is designed for applications under sustained hydrostatic water pressure (basement walls, water tanks, underground water storage), where the substrate is stable and crack movement is minimal. Its crack-bridging capability is limited — it can accommodate hairline (less than 0.1 mm) static cracks only. SikaTop 66 is a flexible elastomeric system — it has a much higher polymer content and cures to a rubbery, elastic membrane with elongation above 80 per cent. It is designed for positive (wet) side or exposed applications where the substrate will undergo thermal movement, concrete creep, or live-load deflection causing micro-cracking in the range of 0.1 to 0.5 mm width. The cured SikaTop 66 membrane stretches with the crack rather than fracturing. Specify SikaTop 107 Seal for: basements, water tanks, underground sumps, and below-grade negative-side waterproofing where hydrostatic pressure is the primary concern and substrate is stable. Specify SikaTop 66 for: exposed roof terraces, podium decks, balconies, bathrooms, and any positive-face application on substrates subject to thermal movement, live loads, or vibration that will cause substrate micro-cracking.

How should SikaTop 66 be applied on an existing concrete roof terrace with an old cement screed and multiple cracks before re-tiling?

For an existing concrete roof terrace with old cement screed and cracks, the preparation and application sequence is: Step 1 — Remove loose, hollow, and cracked screed: tap the screed surface with a hammer to locate hollow-sounding delaminated areas; remove all delaminated and cracked screed by chipping hammer to expose the structural concrete below. Retain sound, well-bonded screed. Step 2 — Surface preparation: clean the remaining screed and exposed concrete surface with high-pressure water at 80 to 100 bar to remove dust, algae, and surface contaminants. Allow to dry to SSD. Step 3 — Fill cracks and voids: fill all cracks wider than 1 mm with Sikaflex 221 polyurethane sealant applied by gun with a backing rod to control depth; fill small holes and voids with Sika repair mortar flush to the surface. Step 4 — Make good missing screed areas: replace removed screed areas with 1:3 OPC:sand mortar screeded flush to surrounding surface; allow to cure minimum 7 days before coating. Step 5 — Apply SikaTop 66: mix Component A (powder) and Component B (liquid) per manufacturer ratio until lump-free. Apply First coat by brush at 1.0 to 1.2 kg per m2, working into the surface and upstands. Allow to firm up (4 to 6 hours at 30 degrees C). Apply Second coat by brush at 1.0 to 1.2 kg per m2 in the opposite direction. For three-coat applications in high-risk or heavily cracked areas, apply a Third coat at 0.5 to 0.8 kg per m2 after second coat has firmed up. Allow minimum 24 hours before tile adhesive application. Apply Sika tile adhesive for tile bed over the cured SikaTop 66 without additional primer.

What is the curing and protection requirement for SikaTop 66 during the Delhi NCR summer and monsoon seasons and what tiles can be laid over the coating?

SikaTop 66 curing and protection requirements in Delhi NCR summer and monsoon conditions. During application and curing: minimum ambient temperature for SikaTop 66 application is 5 degrees C (not relevant for Delhi NCR summer) and maximum ambient temperature is 40 degrees C. On rooftop terraces in May to June in Delhi, the concrete surface temperature in direct afternoon sunlight can reach 55 to 65 degrees C — at these temperatures, the SikaTop 66 coating dries too rapidly, producing a porous, low-strength film rather than a continuous, dense membrane. To avoid this: apply SikaTop 66 in the early morning (5:00 to 9:00 when surface temperature is below 40 degrees C) or shade the work area with temporary polythene sheeting during application and for the first 2 hours of curing. If the surface is visibly hot to the touch, dampen with water and allow to cool to below 40 degrees C before applying the next coat. During monsoon (July to September): protect freshly applied SikaTop 66 from rain for minimum 2 hours after each coat (until the surface is touch-dry and cannot be washed off by rain). If rain is forecast within 2 hours of intended application, postpone. After full cure (all coats applied and 24 hours elapsed), the cured SikaTop 66 is fully rain and water resistant. Tiles over SikaTop 66: any cement-based tile adhesive (Sika TileFix, standard OPC:sand tile adhesive) can be used over cured SikaTop 66. Do not use epoxy tile adhesive as the first bond layer over SikaTop 66 — the epoxy adhesive can debond from the flexible cementitious membrane if the membrane deflects under tile load.