Frequently Asked Questions

What is the complete Nafuflex 2K application procedure for waterproofing the inner face of a new reinforced concrete basement, and how does it differ from positive-side external waterproofing in terms of performance and application sequence?

Inner-face (negative-side) waterproofing of a basement using MC-Bauchemie Nafuflex 2K is the approach used when the external face of the basement wall has not been waterproofed during construction (either because the wall was constructed against existing building foundations without excavation access, or because the external waterproofing has already failed and excavation is impractical for remediation). The complete Nafuflex 2K inner-face application procedure is as follows. Step 1 — Surface preparation. The inner concrete surface must be sound, clean, and free of laitance, form-release agent, oil, paint, existing waterproofing coatings, and all contamination that would impair adhesion. Remove laitance by wire brushing, grinding, or grit blasting. Repair all honeycombed areas with MC-Bauchemie MC-RocTec R (rapid-setting repair mortar) or equivalent repair mortar, allowed to cure for 24 hours. Step 2 — Stop active water leaks. Any active water leaks through cracks or construction joints must be stopped before Nafuflex 2K application, as the cementitious slurry cannot set correctly under flowing water. Inject active leaks with MC-Injekt 2700 HV (PU foam injection) and allow to cure for 24 hours. For minor seepage points, plug with a rapid-setting hydraulic cement such as MC-Bauchemie MC-Stop or equivalent, allow to cure for 1 hour. Step 3 — Pre-wet the substrate. Saturate the concrete substrate with clean water by flooding or repeated sponging until the surface is dark (saturated surface dry condition). This prevents the dry concrete from absorbing water from the freshly applied Nafuflex 2K slurry before the cementitious binder can hydrate. Step 4 — Mix Nafuflex 2K. Pour the full contents of Component A (liquid) into a clean mixing bucket. Add Component B (powder) gradually while mixing with a low-speed electric paddle mixer. Mix for 3 to 5 minutes until a smooth, lump-free slurry is obtained. Allow a 2-minute slake period, then briefly re-mix. Mix only the quantity that can be applied within 20 to 30 minutes (reduce batch size in Indian summer above 35 degrees C). Step 5 — First coat application. Apply the first coat of Nafuflex 2K slurry using a stiff-bristle masonry brush, scrubbing the material firmly into the concrete surface to ensure full penetration of the surface pores. Coverage: 0.8 to 1.0 kg per square metre of mixed material. At all floor-wall junctions and construction joints, embed a reinforcement mesh (fibre mesh tape or Nafuflex reinforcing fleece) into the wet first coat at this stage and brush additional slurry over the mesh to fully encapsulate it. Step 6 — Second and third coat. Allow each coat to firm (surface becomes touch-dry, typically 4 to 6 hours) before applying the next coat perpendicular to the previous. Third coat is essential for maximum hydrostatic resistance. Total consumption: 2.0 to 2.5 kg per square metre. Step 7 — Curing. Protect the applied membrane from direct sun, wind, and rain for a minimum of 72 hours. Mist with water twice daily for 7 days in hot, dry Indian conditions to prevent premature drying and surface cracking of the cementitious matrix. Regarding the comparison with positive-side external waterproofing: positive-side external waterproofing (applied to the external face of the basement wall, in contact with the soil and ground water) is the preferred and most structurally correct approach, as the water pressure acts to press the membrane against the concrete wall rather than to peel it off. Nafuflex 2K applied on the positive (external) side has the hydrostatic water pressure working in its favour, pressing it into the concrete and enhancing bond. On the negative (inner) side, hydrostatic pressure acts against the membrane — trying to push it off the wall surface — and the membrane relies entirely on its adhesion to the concrete substrate to remain in place. This is why inner-face (negative-side) waterproofing is technically inferior to outer-face (positive-side) waterproofing. However, Nafuflex 2K is specifically tested and rated for negative-side hydrostatic resistance at 7 bar, meaning it can be reliably used on inner faces where positive-side application is impossible, provided surface preparation is thorough and the application is correctly supervised.