Frequently Asked Questions

On a Noida parking structure rehabilitation project involving 4,500 square metres of spalled and delaminated slab soffit concrete across 6 floors of a 10-year-old multi-storey car park, how should the contractor plan the machine spray repair operation with MC-Nafuplan HD to maximise productivity while ensuring structural quality and minimising disruption to the building during the repair programme?

Rehabilitating 4,500 square metres of delaminated parking structure slab soffit across 6 floors — a typical scenario for multi-storey car parks in Noida and the Delhi NCR urban belt where reinforcement corrosion from vehicle-tracked chloride and carbonation progresses aggressively in the first 10 to 15 years after construction — is a project that rewards careful pre-construction planning for the spray mortar repair operation. At this scale, machine spray application with MC-Nafuplan HD is the only practical approach: hand application at this area would require 3 to 4 times the labour and 2 to 3 times the programme duration. The planning methodology is as follows. Phase 1 — Floor-by-floor condition survey: before starting repair work, complete a systematic delamination survey of every floor soffit using the chain drag or hammer tap test (IS 13311 Part 1) to map all delaminated areas on scaled floor plans. Use phenolphthalein indicator solution applied to freshly drilled cores or exposed concrete faces to determine the carbonation depth profile — in a 10-year-old Delhi NCR parking structure with indoor-but-ventilated environment, carbonation depths of 15 to 25 mm are typical, and where the carbonation front has reached the reinforcement (typically 25 to 30 mm cover in older construction), corrosion will be active. Measure chloride content from powder samples at 10 and 20 mm depth — vehicle-tracked chloride in uncovered parking structures can produce chloride concentrations at 20 mm depth of 0.2 to 0.4 percent by mass of concrete, approaching or exceeding the corrosion threshold. Mark all delaminated areas and all areas with active corrosion (orange or brown staining indicating corrosion bleed-through) for priority repair. Calculate the total area of full section repair (delaminated, steel exposed), shallow surface repair (carbonated but not delaminated), and protective overlay (currently sound but at risk). Phase 2 — Zoning and programme: divide the 4,500 square metres across 6 floors into repair zones matched to the floor plate area per floor (average 750 square metres per floor). Plan to repair one floor at a time — close each floor to vehicle traffic during the repair phase and cure period (minimum 10 to 14 days per floor) to avoid vibration damage to fresh mortar and to provide a safe working platform for the spray team below. Plan the programme to start on the highest floor and work downward so that spray rebound and material drip does not contaminate freshly repaired lower floors. Alternatively, if the building management requires at least partial operation during the repair programme, plan a 50 percent zone-per-floor approach — repair the east half of each floor first, reopen to traffic, then repair the west half. A typical programme for 4,500 square metres with a two-crew spray operation is 8 to 12 weeks depending on extent of delamination and rebar work. Phase 3 — Equipment and crew: the spray mortar operation requires: one rotor-stator mortar pump (capacity 20 to 30 litres per minute, suitable for MC-Nafuplan HD particle size up to 8 mm) or a purpose-designed concrete spray unit; one 25 mm internal diameter delivery hose (25 to 50 metres length to reach from ground-level pump to upper floors, or locate pump on each floor with separate material supply); a water addition unit on the pump for consistent water-to-powder ratio; one spray nozzle operator (the nozzle person is the skill centre of the operation — their distance, angle, and speed of nozzle movement controls layer thickness, density, and surface finish); one mortar mixer operator feeding the pump; and one QC person monitoring spray layer thickness with a pin-type wet film gauge and collecting fresh mortar samples for cube specimens. Plan for one bag of MC-Nafuplan HD (25 kg) to cover approximately 0.5 to 0.8 square metres at 25 to 30 mm thickness — so for 4,500 square metres at an average 25 mm thickness, plan for approximately 5,600 to 9,000 bags (140 to 225 tonnes of product). Phase 4 — Spray operation procedure: prepare each area by: removing all loose and delaminated concrete by hydrodemolition or jack-hammer (jack-hammer acceptable for slab soffit where vibration risk to the floor above is managed by limiting frequency), cleaning rebar to St 2 cleanliness and applying Compliform 12 rebar primer, and pre-wetting the prepared concrete substrate with water (saturated surface dry condition) 30 to 60 minutes before spray. Mark the required spray thickness on the substrate using depth pins (cut rod sections) at 1.0 metre grid spacing and attached to the substrate with tape — the nozzle operator uses these as visual guides to build the correct thickness. Spray at 0.3 to 0.6 metre nozzle-to-surface distance, holding the nozzle perpendicular to the surface, and build the layer in two or three passes (avoiding a single thick pass which causes sagging) at a movement rate calibrated by trial to the required thickness. Collect two 150 mm cube samples from the fresh mortar per 50 square metres sprayed per day, and mark the pour reference and date for 7-day and 28-day compressive strength testing. Phase 5 — Curing: spray MC-Cure acrylic curing compound over the entire repaired surface area immediately after the spray mortar achieves the tack-free surface condition (typically 2 to 4 hours after spray in Noida indoor-garage conditions at 28 to 38 degrees Celsius). Apply curing compound at the specified rate (approximately 0.2 litres per square metre) using a hand-pump garden sprayer. Prevent direct vehicle access to repaired soffits for a minimum 14 days (vibration from vehicles on the floor above the repaired slab soffit is acceptable after 3 days). Space Arc Engineering supplies MC-Nafuplan HD, Compliform 12 rebar primer, and MC-Cure curing compound in bulk pallet quantities for parking structure and infrastructure rehabilitation projects across Noida, Ghaziabad, Delhi NCR, and Uttar Pradesh, and can provide technical support for spray mortar trial panels and machine calibration prior to full repair programme start.