Frequently Asked Questions

What is the correct way to prepare and apply the Nitobond SBR bonding slurry before a repair mortar?

The Nitobond SBR bonding slurry is prepared by mixing Nitobond SBR latex with cement and water in the proportions specified in the product data sheet — typically approximately 1 part SBR to 1 part cement to 1 part water by volume, producing a creamy slurry consistency. The slurry is brush-applied to the mechanically prepared and pre-wetted (saturated surface-dry) substrate surface, covering all areas to be repaired. The critical application timing rule is: apply the repair mortar while the SBR bonding slurry is still tacky — not wet (which would dilute the mortar at the interface) and not dry (which would form a weak non-bonding film). The tacky window at 25 to 30 degrees Celsius ambient is typically 15 to 30 minutes. In hot summer conditions with higher evaporation rate, the window is shorter — the repair crew must be ready to place the mortar immediately the primer has reached the tacky state. Never allow the SBR bonding slurry to dry completely before the repair mortar is placed.

Can Nitobond SBR be used as a waterproofing admixture in a flat roof cementitious coating?

Yes. Nitobond SBR is widely used as a polymer admixture in cementitious waterproofing coatings applied on flat roofs, water tanks, and basement walls. The standard approach is to use Nitobond SBR as both the primer (applied as a bonding slurry to the cleaned concrete surface) and as the admixture in the cement-sand waterproofing render or coating applied over the primer. A typical waterproofing mortar using Nitobond SBR contains 1 part cement, 1.5 to 2 parts clean sand, and 0.30 to 0.40 litres of Nitobond SBR per kg of cement in place of part of the mixing water. This produces a mortar with significantly lower water absorption and permeability than a standard cement-sand mix. For the highest waterproofing performance, two coats of the SBR-modified mortar should be applied — the first coat to the prepared primed substrate and the second coat applied at right angles to the first after the first coat has cured. The resulting two-coat waterproof system is suitable for flat roofs, water tanks, and basement walls.

What is the difference between Nitobond SBR and Nitobond AR for bonding repair mortars to concrete?

Both Nitobond SBR and Nitobond AR are polymer bonding agents from Fosroc used to improve the bond between repair mortars and concrete substrates, but they use different polymer chemistries with different performance profiles. Nitobond SBR uses styrene-butadiene rubber (SBR) latex — a rubbery, flexible polymer that provides good adhesion improvement, flexibility in the bonding interface, and moderate water resistance. Nitobond AR uses acrylic polymer — typically a polyacrylate latex that provides good adhesion improvement with slightly better UV resistance and better compatibility with coloured renders and decorative coatings. For standard structural concrete repair with cementitious repair mortars, both products perform well as bonding agents. For decorative renders, coloured coatings, or external surfaces with UV exposure, Nitobond AR may be preferred for its better UV stability in the bonding interface. For applications requiring maximum waterproofing modification of the mortar, Nitobond SBR has a longer track record in waterproofing applications. Space Arc Engineering can advise on the most appropriate bonding agent for the specific project requirements.