Frequently Asked Questions

How does Renderoc M differ from Renderoc HB2 and when should I choose one over the other?

Renderoc HB2 is specifically formulated as a high-build hand-applied mortar with coarser aggregate and a stiffer working consistency that allows application in thicker single coats (up to 50 mm or more per coat) on overhead and vertical surfaces without sagging. Renderoc M is a medium-aggregate product that is slightly less stiff and slightly easier to trowel and finish. In practice, Renderoc M is preferred for repairs where the surface quality and trowelling of the finish are more important, or where repair depths are moderate (15 to 50 mm), while Renderoc HB2 is preferred for deeper single-coat applications and for overhead soffits where the higher-build characteristic is critical. For most general concrete repair work on columns, beams, and bridge elements, both products are technically acceptable — the choice may be based on regional availability, contractor familiarity, or the specific finish requirement.

Is a bonding primer required before applying Renderoc M?

Yes. Renderoc M and all Renderoc repair mortars require a bonding primer applied to the prepared substrate. Nitobond EP (two-component epoxy bonding agent) or Nitobond SBR (single-component polymer slurry) are the appropriate Fosroc primers. The substrate must first be mechanically prepared (scabbling, grinding, hydrodemolition, or shot blasting) to remove carbonated, contaminated, or weak concrete and expose sound aggregate, then the prepared surface must be saturated to surface dry condition before priming. Applying any repair mortar without proper surface preparation and priming is the most common cause of repair failure — the repair debonds from the substrate, often visible as a hollow sound under tap testing within 6 to 12 months of the repair.

Can Renderoc M be used for waterproof concrete repair in a basement?

Renderoc M is a structural repair mortar, not a dedicated waterproof repair mortar. For below-grade repairs in basements where water pressure or high moisture is present, a polymer-modified mortar like Renderoc M provides improved water resistance compared to plain cementitious repair, but may not be adequate as a standalone waterproof system under significant hydrostatic head. For basement waterproofing repairs, the Renderoc mortar repair should be combined with a waterproof coating system applied over the repair after it has cured — such as Brushbond TGP, Nitoproof 100, or the Fosroc Proofex system — to provide the waterproof barrier. Consult Space Arc Engineering for a complete basement repair and waterproofing system specification appropriate to the water head and soil conditions at the specific site.