Frequently Asked Questions

What spray equipment is used to apply Renderoc Spray HBL and can a standard plastering machine be used on site?

Renderoc Spray HBL is designed for application using a continuous mixer and pump system (wet spray) or a dry-mix shotcrete machine (dry spray) — these are specialised pieces of equipment used in concrete repair and shotcrete work, distinct from the small hand-held plastering machines (often called puff machines or texture coaters) sometimes used for finish coat plasters on walls. A standard small plastering machine as used by plastering subcontractors in building work in India is NOT suitable for applying Renderoc Spray HBL — the high density (even though lightweight for a repair mortar, Renderoc Spray HBL is still a high-density material compared to finish plaster), the aggregate size in the mortar, and the requirement for a consistent, controllable delivery pressure for overhead spray application all require specialised spray equipment. The most common spray method for Renderoc Spray HBL in India on infrastructure rehabilitation projects is the wet spray method: the dry Renderoc Spray HBL powder is pre-mixed with water in a continuous mixer to a fluid pumped consistency, then delivered under pressure through a flexible hose to a spray nozzle where it is applied to the prepared concrete surface. The spray operator controls the spray distance, angle, and material build-up to achieve the required thickness and compaction. For very large projects (bridge rehabilitation, tunnel lining repair), a dry-mix shotcrete system may be used, with the dry Renderoc Spray HBL powder fed through the dry-mix machine and water added at the nozzle. Space Arc Engineering can advise on spray equipment suppliers and specialist spray application contractors in Delhi NCR for Renderoc Spray HBL projects.

What surface preparation is needed before applying Renderoc Spray HBL and is the preparation requirement different from hand-applied Renderoc repair mortars?

The surface preparation requirements for Renderoc Spray HBL are the same in principle as for hand-applied Renderoc repair mortars — both systems require a sound, clean, roughened concrete substrate with a surface profile (roughness) adequate for mechanical bond between the repair mortar and the substrate. The specific preparation methods and the minimum required surface profile for spray application may be slightly different in practice because spray-applied mortar arrives at the surface with higher kinetic energy (the material is travelling at speed when it strikes the substrate) than hand-applied mortar, which means spray application can achieve adequate bond even on surfaces that are slightly less well-prepared than required for hand application. However, this should not be taken as a reason to reduce preparation quality — the preparation standard for Renderoc Spray HBL should be: remove all carbonated, contaminated, and delaminated concrete by abrasive blasting (hydro-blasting at high pressure is particularly effective for large areas) or by mechanical chipping and grinding; expose all corroded reinforcement by chipping back the concrete behind the bar to a minimum of 10 to 15 mm clear behind the full bar perimeter; clean and treat exposed reinforcement with Fosroc Nitoprime Zincrich (zinc-rich primer) to halt corrosion and provide a non-corrosive interface between rebar and repair mortar; apply Nitobond EP epoxy bonding agent (two-coat system: primer coat and adhesive coat applied wet-on-wet immediately before mortar application) to the prepared substrate to maximise adhesion and create a chemically bonded interface between the old concrete and the repair mortar; and form square-cut edges at the perimeter of the repair area (saw-cut to 10 mm depth) to prevent feather-edge repair mortar that cracks and debonds around the repair boundary.

How thick a layer can Renderoc Spray HBL be applied in a single pass and what is the maximum total thickness that can be built up on an overhead soffit?

The maximum thickness that can be applied in a single spray pass with Renderoc Spray HBL on an overhead soffit is a balance between the spray equipment settings, the material consistency, the ambient temperature, and the ability of the applied layer to support its own weight before the initial set provides sufficient stiffness. For a lightweight polymer-modified mortar in typical Indian site conditions (25 to 35 degrees Celsius), a single overhead spray pass of 15 to 25 mm is generally achievable without slump or fallout, compared to 10 to 15 mm for a standard-density repair mortar in the same conditions — the lightweight formulation is specifically advantageous in this respect. In very hot conditions (above 35 degrees Celsius at the substrate), the rapid surface drying and accelerated set can actually help hold a thicker single pass, but the risk of plastic shrinkage cracking increases in hot, dry, windy conditions. For total repair thickness greater than 25 to 30 mm on an overhead soffit, the repair is built up in multiple passes: the first pass of 15 to 20 mm is applied and allowed to reach initial set (typically 30 to 60 minutes in Indian conditions), and then the second pass is applied to bring the total thickness to the required level. Before applying the second pass, the surface of the first pass should be lightly scratched to provide a mechanical key for the second pass. For very deep repairs (50 to 100 mm or more of concrete loss) on overhead soffits — as found on severely deteriorated bridge deck undersides with extensive reinforcement corrosion — the repair system may require multiple thin spray passes with set times between passes, or the use of Conbextra grout-backed formwork with pumped Renderoc grout for the deepest areas, with Renderoc Spray HBL as the final reprofile coat.