About Fosroc Nitobond HAR

Fosroc Nitobond HAR is a ready-to-use, single-component bonding agent built around a modified acrylic emulsion that resists hydrolysis, meaning it does not break down in the presence of moisture. This single property is what separates it from cheaper PVA-based bonding agents, which re-emulsify when wet and lose their grip in external or perpetually damp conditions. Within the Fosroc system, Nitobond HAR is positioned as the recommended primer for the Renderoc range of cementitious repair mortars, where it provides the critical adhesive link between hand-applied repair material and the prepared concrete substrate. For Indian contractors, consultants and structural-repair specialists, it is one of the most widely specified bonding aids on patch-repair, spalling-concrete and re-plastering jobs because it is forgiving to use, water-cleanable, non-flammable and economical in coverage. Nitobond HAR adheres strongly to concrete, masonry, stonework, plaster and block board, and it is compatible with all common hydraulic cements, so it slots into both proprietary Fosroc repair systems and conventional site-batched cement-sand mortars. Beyond priming, it can be gauged into a cement-sand slurry or mortar to improve the tensile and flexural behaviour of thin-section repairs and screeds. It is supplied in 1 litre, 5 litre and 20 litre packs (Fosroc codes FC322070-1L, -5L and -20L), making it practical for everything from small snag-list repairs to large rehabilitation contracts. As an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, Space Arc Engineering supplies genuine, batch-traceable Nitobond HAR along with the matching Renderoc mortars and Nitoprime/Nitobond accessories needed to complete a specification correctly.

The technical insight

The performance of Nitobond HAR comes from its acrylic (rather than vinyl-acetate/PVA) polymer chemistry. When the emulsion is brushed onto a saturated surface-dry substrate it forms a tacky polymer film that the fresh mortar keys into; as the mortar cures, the polymer co-films with the cement matrix and stitches the new mortar to the old concrete. Because the acrylic backbone is hydrolysis-resistant, the bond line survives wetting and re-wetting cycles, which is why Fosroc clears it for external use whereas PVA agents are restricted to permanently dry interiors. The single most important on-site discipline is timing: the Renderoc or cement mortar must be placed while the primer is still tacky. If the film is allowed to dry fully before mortaring, the area must be re-primed; if it is applied too wet, vertical and overhead build-up of mortar becomes difficult and may slump. Where the substrate is wet, likely to remain permanently damp, or where a moisture barrier between substrate and repair is required, Fosroc’s own guidance is to switch to the epoxy-based Nitobond EP rather than Nitobond HAR. It must also be understood that Nitobond HAR is a bonding aid, not a curing membrane, and it is generally not used as a primer when Renderoc mortars are spray-applied.

Where it is used

• Priming prepared concrete before hand-applied Renderoc repair mortars on spalled, cracked or carbonated concrete
• Bonding new cement-sand plaster, render and screeds to existing concrete and masonry substrates
• Gauging liquid mixed into cement-sand slurry to make a bonding bridge for thin-section repairs
• Repair of beams, columns, soffits, chajjas and other RCC members where overhead and vertical adhesion is needed
• Re-plastering of external facades, parapets and boundary walls exposed to rain and damp
• Patch repairs on masonry, stonework, block board and plaster within building rehabilitation contracts
• Bonding feather-edge and thin topping repairs that would otherwise debond from a smooth substrate

Key advantages

• Single component and ready to use straight from the container, with no site mixing or pre-batching required
• Hydrolysis-resistant acrylic chemistry, so it remains effective in external and intermittently damp locations unlike PVA bonding agents
• Develops high bond strength between repair mortars and concrete, masonry, plaster and stonework
• Improves the tensile and flexural properties of the mortar it is gauged into
• Good vertical and overhead grab, supporting build-up of repair mortar on soffits and columns
• Economical coverage of roughly 4-6 m2 per litre as a primer
• Non-flammable and water-based, with simple clean-up using clean water
• Compatible with all common hydraulic cements, so it suits both proprietary and site-batched mortars

Limitations & considerations

• Not a curing membrane and must not be relied on to retain mix water in fresh concrete or mortar
• Must not be applied when the ambient temperature is below 5 degrees C and falling
• Repair mortar must be placed while the primer is still tacky; if the film dries the surface has to be re-primed
• If applied too wet, vertical and overhead build-up of mortar can be difficult and may slump
• Not the correct choice where the substrate is wet, permanently damp, or needs a moisture barrier; Nitobond EP epoxy bonding aid should be used instead
• Generally not used as a primer when Renderoc mortars are applied by spray
• Being water-based, it must be protected from frost in storage and on site

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitobond HAR

Within the Fosroc repair ecosystem, Nitobond HAR sits as the standard acrylic bonding primer for the Renderoc mortar family and is the natural partner to products such as Renderoc HB, Renderoc Plug and Nitoprime Zincrich (the anti-corrosion reinforcement primer used alongside it in a full repair sequence). It steps up from the basic Nitobond AR grade through its hydrolysis resistance, and it hands over to the two-part epoxy Nitobond EP whenever conditions are wet, permanently damp, or demand a moisture barrier. Against the wider Indian market it competes directly with Sika’s SikaLatex / Sika Latex Power and Sikadur-32 epoxy bonding agent, MBS (MYK Arment) and Pidilite Dr. Fixit Pidicrete URP and Bondaid for acrylic/SBR bonding agents, and STP (Shalimar) bonding aids. For most external concrete-repair priming where a genuine Fosroc-system match is wanted, Nitobond HAR is the specified choice; where budgets are tight an SBR latex like Pidicrete URP may be considered, and where a fully waterproof, structural old-to-new concrete bond is the priority an epoxy bonding agent such as Nitobond EP or Sikadur-32 is the more appropriate technical solution. Space Arc Engineering can advise on the correct selection and supply the genuine Fosroc product with the matching repair mortars.

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