Frequently Asked Questions

What is the correct mixing ratio and application procedure for using Nitobond SBR as a bonding agent under a new floor screed and what happens if the slurry is allowed to dry before the screed is placed?

Applying Nitobond SBR as a bonding agent for a new floor screed over an existing concrete slab is one of the most common applications in India — it is the standard procedure before laying any bonded floor screed to prevent the screed from debonding and curling up at edges and joints, which is the most frequent defect in floor screed construction in India. The correct application procedure is: surface preparation — the existing concrete substrate must be prepared by shot blasting, scarifying, or at minimum wire brushing to remove all laitance, dust, curing compound, contamination, and any weak or friable surface layer; water the substrate thoroughly before applying the bonding slurry to prevent the dry concrete from absorbing the SBR latex from the slurry too rapidly; bonding slurry preparation — mix Nitobond SBR with cement and water in the ratio 1 part SBR : 1 part ordinary Portland cement : 1 part water (by volume) to form a thick, creamy slurry without lumps or undissolved cement; slurry application — pour the slurry onto the substrate and scrub it vigorously into the surface with a stiff brush or broom, working the slurry into all surface pores and aggregate voids; cover the entire area to be screeded with a uniform coat of slurry without missed areas; screed placement timing — this is the critical timing requirement: the screed mix must be placed onto the SBR slurry while the slurry is still wet and tacky (feels slightly sticky when touched with the back of the hand) — this is the wet-on-wet application window and it is typically 20 to 40 minutes after slurry application (shorter in hot Indian summer conditions when the slurry dries faster). If the SBR slurry is allowed to dry completely before the screed is placed (the surface becomes dry, powdery, and no longer tacky), the bonding function is lost — the dried SBR film becomes a separation layer rather than a bonding agent, and the screed placed over a dried SBR slurry will delaminate. If the slurry dries before the screed is placed, the dried slurry must be removed (by brushing or blowing with compressed air) and fresh slurry applied immediately before the screed pour.

Can Nitobond SBR (SBR latex) replace Nitobond EP (epoxy bonding agent) in a Fosroc concrete repair system and what are the key differences between SBR and epoxy bonding agents?

Nitobond SBR (SBR latex bonding agent) and Nitobond EP (two-component epoxy bonding agent) both serve as bonding agents between old and new concrete or mortar, but they have significantly different performance levels and cost profiles — the selection depends on the required performance of the repair, the nature of the substrate, and the severity of the exposure. The key differences are: bond strength — Nitobond EP (epoxy) provides a much higher bond strength than Nitobond SBR (SBR latex); the epoxy bond strength of Nitobond EP is typically 2 to 3 MPa or higher in pull-off tests on well-prepared concrete, while Nitobond SBR bonding slurry provides bond strengths in the range of 0.8 to 1.2 MPa; for structural repairs where the repair mortar must achieve the code-required minimum 1.5 to 2.0 MPa pull-off bond strength (ICRI, BS EN 1504 requirements), Nitobond EP is mandatory and SBR cannot substitute; chemical and water resistance — epoxy (Nitobond EP) is completely waterproof and highly chemical resistant when cured; SBR (Nitobond SBR) is water-resistant but not waterproof — in permanently wet or submerged conditions, the SBR slurry can gradually re-emulsify and the bond degrades; cost — Nitobond SBR is substantially less expensive than Nitobond EP, making it the preferred choice for large-area, lower-risk applications like floor screeds, renders, and non-structural patching where epoxy performance is not required; temperature sensitivity — SBR is more temperature-sensitive than epoxy; below 10 degrees ambient, SBR latex can freeze and be permanently damaged, while Nitobond EP has a lower cure threshold with appropriate hardener selection. The correct guidance for Indian construction: use Nitobond SBR for floor screeds, waterproof renders, non-structural patches, tile beds, and swimming pool renders; use Nitobond EP for structural concrete repairs, overhead and vertical repairs on bridges and structures, and repairs in permanently wet or chemically exposed zones.

What is the recommended SBR addition rate when using Nitobond SBR as a polymer admixture in a waterproof basement render and how much does SBR modification reduce the water permeability of cement render?

When using Nitobond SBR as a polymer admixture in a waterproof cement render for basement or podium waterproofing, the recommended addition rate is typically 1 part Nitobond SBR latex to 3 parts water in the gauging water (i.e., for every 3 litres of water used to mix the render, replace 1 litre with Nitobond SBR latex and use only 2 litres of water) — giving an SBR:water ratio of 1:3 in the gauging solution. At this addition rate, the polymer content of the cured render dry film is sufficient to bridge micro-cracks, reduce inter-particle porosity, and create a partially hydrophobic matrix that significantly reduces water vapour transmission and liquid water penetration. For a more intensively modified waterproof render (higher SBR polymer content), the ratio can be increased to 1 part SBR to 2 parts water (1:2 SBR:water), which provides higher polymer content and correspondingly better waterproofing and flexibility, but at higher cost. The permeability reduction from SBR modification of cement render is significant: unmodified OPC cement render (mixed with water only) has a water permeability of approximately 1 x 10-11 to 1 x 10-12 m/s under standard test conditions; SBR-modified cement render (1:3 SBR:water addition) reduces permeability by approximately one to two orders of magnitude, to approximately 1 x 10-13 m/s. This permeability reduction is sufficient for exposed external wall renders where the render must resist wind-driven rain, and for internal basement renders where water vapour transmission and minor seepage must be controlled. For actively leaking basements with significant hydrostatic water pressure (greater than 0.3 bar positive or negative pressure), SBR-modified render alone is not sufficient — a fully waterproof membrane system (Proofex 30, Nitoproof 400, or Cemseal crystalline system) is required in addition to or instead of the polymer-modified render.