Frequently Asked Questions

When should Nitobond AR be specified instead of Nitobond SBR as the bonding agent for a repair mortar?

The choice between Nitobond AR (acrylic) and Nitobond SBR (styrene-butadiene rubber) for a repair mortar bonding agent is primarily driven by the exposure conditions of the repair and the type of finish system applied over the repair. For external concrete repairs and renders that are directly exposed to sunlight and weathering without a further coating over the repaired area — or where the repair is part of an external decorative render system — Nitobond AR is preferred because the acrylic polymer has better UV resistance and better compatibility with coloured pigmented render systems. For structural concrete repairs under protective coatings (anti-carbonation paint, waterproofing membrane), for water tank repairs, and for internal repairs, Nitobond SBR is equally suitable and has a longer track record in waterproofing modification. Both products improve adhesion, reduce permeability, and improve mortar flexibility — the UV stability and coloured render compatibility of acrylic is the main practical differentiator for external exposed applications.

Can Nitobond AR be used in a sand-cement screed over an existing concrete floor?

Yes. Nitobond AR can be used in both the bonding slurry and the screed mortar for a bonded sand-cement screed applied over an existing concrete floor. The existing concrete floor must first be mechanically prepared by shot blasting, scabbling, or grinding to remove laitance and expose clean aggregate. The Nitobond AR bonding slurry is then brush-applied to the dampened prepared surface and the screed mortar — incorporating Nitobond AR as a polymer admixture — is placed while the slurry is still tacky. The polymer modification of the screed mortar with Nitobond AR reduces plastic and drying shrinkage (one of the main causes of screed delamination), improves adhesion to the concrete base, and increases the tensile strength of the screed — all of which improve the long-term performance of the bonded screed under foot traffic, wheeled traffic, and thermal movement.

What surface preparation is required before applying the Nitobond AR bonding slurry on a concrete wall for render?

The concrete wall surface must be clean, sound, and free of any material that would reduce the bond between the bonding slurry and the substrate. The preparation requirements are: remove any existing paint, coating, or contamination (oil, grease, curing compound) by mechanical means (grinding, wire brushing, grit blasting, or high-pressure water jetting as appropriate to the contamination type); remove any loose, soft, or carbonated surface concrete to expose clean aggregate; repair any cracks or defects in the wall before rendering; and pre-wet the prepared surface to a saturated surface-dry condition before applying the bonding slurry (the pre-wetting prevents the dry concrete from absorbing water from the fresh bonding slurry too rapidly). On concrete surfaces that are very smooth (cast against steel or phenolic shuttering), the smooth surface should be mechanically roughened to provide a better mechanical key before the bonding slurry is applied. The slurry should be applied by stiff brush (not roller) to ensure good penetration into the surface texture.