Frequently Asked Questions

How does Renderoc RG achieve such rapid early strength compared to ordinary repair mortars?

Renderoc RG uses rapid-hardening cement technology based on calcium sulphoaluminate (CSA) cement or similar rapid-gain cement chemistry, which hydrates much faster than ordinary Portland cement. In CSA-based systems, the primary hydration reaction produces ettringite (a calcium sulphoaluminate hydrate) within minutes of water addition, causing very rapid early stiffening and strength development. Ettringite is a benign expansive product in controlled CSA cement systems and contributes to the low-shrinkage behaviour of rapid-gain mortars. The rapid hydration releases heat quickly, which further accelerates the strength gain rate. The result is a mortar that achieves in 2 to 4 hours what ordinary Portland cement mortar achieves in 24 to 48 hours.

Does Renderoc RG require a bonding primer like other Renderoc repair mortars?

Yes. Even though Renderoc RG is a rapid-gaining mortar, good bond to the existing concrete substrate is still required for the repair to be structurally effective and durable. Nitobond EP (epoxy bonding agent) or Nitobond SBR (polymer slurry) should be applied to the prepared concrete substrate before placing Renderoc RG. The substrate must be mechanically prepared (scabbling, grinding, or shot blasting to remove weak concrete and provide aggregate exposure) and must be at the saturated surface dry condition. In very fast-track repairs, a fast-cure bonding agent or a compatible slurry of the same rapid-gain cement can be used as a primer. The working time after mixing Renderoc RG is short (typically 5 to 10 minutes at 20 deg C), so all preparation and priming must be complete before mixing the mortar.

Does ambient temperature affect the early strength development of Renderoc RG?

Yes, significantly. At higher temperatures (above 25 degrees C), the hydration reaction of Renderoc RG is accelerated — early strength development is faster and the return-to-service time is shorter. This is advantageous in Indian summer conditions. At lower temperatures (below 15 degrees C), the rate of hydration slows and the early strength development is delayed — at 5 degrees C, the 2-hour strength may be significantly lower than at 20 degrees C, and the return-to-traffic time must be extended accordingly. In cold weather repair work, warming the mixing water and the aggregate, and protecting the fresh repair from cold ambient air with insulated blankets, can help maintain adequate reaction temperature for fast strength gain. Do not attempt rapid-gain concrete repair at temperatures below 5 degrees C without specific cold-weather precautions.