Frequently Asked Questions

What is the correct procedure for dry-packing a 100 mm diameter, 200 mm deep core hole in a structural concrete column in Ghaziabad using MC-Nafufill KD, and how should the bond between the dry-pack mortar and the existing concrete be ensured to prevent the repair from falling out or losing contact with the hole walls?

Repairing a 100 mm diameter, 200 mm deep core test hole in a structural concrete column using MC-Nafufill KD dry-pack mortar requires careful attention to surface preparation, consistency control, placement technique, and curing to achieve the dense, fully bonded, high-strength repair needed in a structural element. The following procedure should be followed. Step one — substrate preparation: the core hole interior must be prepared to receive the dry-pack mortar. Using a wire brush or air-operated chipping tool, abrade the smooth saw-cut interior surface of the core hole to create a rough texture — the smooth, glassy surface left by diamond core drilling must be roughened to ICRI CSP 2 to CSP 3 (light roughening) to provide adequate mechanical interlock for the dry-pack mortar. Do not saw-cut or ream the hole to enlarge it — the circular cylindrical geometry is acceptable. Remove all dust, core drilling residue, and cooling water from the hole using a stiff brush and clean compressed air. The hole must be surface-dry or very slightly damp (saturated surface dry) before priming — do not place mortar into a wet or dripping hole. Step two — apply bonding primer: brush apply a full coat of an appropriate MC-Bauchemie bonding primer (neat cement slurry mixed with a polymer bonding agent, or MC-Pox 1K epoxy primer if maximum bond is required) to the entire interior surface of the hole using a narrow brush or swab applicator. Ensure all surfaces — the cylindrical wall and the bottom of the hole — are fully coated. Allow the primer to reach tack-free stage before applying the first mortar lift — do not allow the primer to fully dry and lose tack. Step three — mix MC-Nafufill KD: weigh or measure the minimum water needed to produce the correct dry-pack consistency. Begin with 0.12 litres of water per kilogram of powder, add the powder to the water in a clean bucket, and mix with a stiff palette knife or by hand until a uniform paste is obtained. Test the consistency: the mortar should form a ball when squeezed in the palm that just holds its shape without crumbling (too dry) or slumping (too wet). If the ball crumbles and does not cohere, add water in very small increments (10 ml at a time) until the ball just coheres. Resist the temptation to add more water than necessary — each increment of excess water raises the water-cement ratio, reduces the compressive strength, and increases drying shrinkage of the cured mortar. Step four — dry-pack placement: place the first mortar lift into the bottom of the hole to approximately 30 to 40 mm depth. Using a hardwood or steel rod of 20 to 25 mm diameter (slightly smaller than the hole diameter), compact the mortar firmly from the centre outward and against the hole wall, using short, firm jabbing strokes at 10 to 15 mm centres across the mortar surface until the mortar is densely compacted and no further settling occurs under rod pressure. The mortar should be visibly dense and fully in contact with the hole walls after compaction — any voids or gaps at the mortar-wall interface must be eliminated by further rodding. Add the next 30 to 40 mm lift of mortar onto the compacted first lift and repeat the compaction procedure, ensuring good contact between successive lifts by roughening the previous lift surface with the rod tip before adding the next lift. Continue until the hole is filled to within 5 to 10 mm of the concrete surface. Step five — final surface preparation: for the final lift, bring the mortar slightly proud of the surrounding concrete surface, then strike off flush and finish smooth with a steel trowel to match the concrete surface texture. If the column surface has a bush-hammered or formed texture, replicate the texture in the repair surface while the mortar is still fresh. Step six — curing: immediately apply a curing compound (MC-Cure) over the repaired hole surface and, if possible, cover the repair with wet hessian taped in place for 24 hours. In hot Indian summer conditions, keeping the repair damp for 3 to 5 days significantly improves the mortar hydration and final strength. Ensure the repair is not subjected to vibration, impact, or mechanical loading for at least 24 hours (preferably 72 hours) until adequate strength is achieved. Space Arc Engineering supplies MC-Nafufill KD and provides technical guidance for structural concrete core hole and confined repair applications across Delhi NCR, Ghaziabad, Noida, and Uttar Pradesh.