RonaBond HB40 mortar is used for repairing concrete on vertical and overhead surfaces where ease of application is as important as strength. RonaBond HB40 can be applied in relatively thick section to walls and soffits and, depending on the nature of the repair, in layers up to 75mm depending on size and orientation.

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• Features & Benefits
• Case Studies
• Preparation of Concrete and Steel
• Wetting and Priming
• Mixing
• Application
• Curing
• Test Data

Features & Benefits

• High build repair mortar
• Repairs up to 75mm in single application
• Use for structural repairs
• High strength
• Easy to use
• Pre-packed for control and convenience
• Waterproof
• Frost proof
• Install from 6mm

Case Studies

Addenbrooke’s Hospital

Concrete repairs to the nurses' accomodation high-rise block at Grantchester House, restoring facades.

Preparation of Concrete and Steel

All concrete identified for removal must be broken out to ensure that repair materials are applied to a sound and stable substrate and that the minimum mortar thickness can be applied throughout. Repair edges must be saw cut at an angle of 90 degrees to the plane of the concrete, to avoid feather edging.

Reinforcing steel in the repair area must be exposed to its full circumference, until uncorroded steel is visible, to a sufficient depth for adequate cleaning of the bar, Loose rust and scale must be removed.

Cover to reinforcement must be ≥15mm to ensure adequate protection of steel and prevent reflective cracking.

Corroded steel must be replaced where necessary.

All removal of concrete and steel must be carried out in accordance with the specification.

When repairing chloride contaminated concrete the method used to prepare and prime surfaces may differ - consult Rawlins Technical on 0113 2455450 (option 2) or send a message to [email protected].

All surfaces must be cleaned to remove loose dust, debris and surface contamination which may prevent adhesion of the repair mortar to concrete and steel. Concrete must be clean and prepared with a scabbler or needle gun.

Wetting and Priming

Following preparation of concrete and steel, thoroughly wet all concrete surfaces to be repaired with clean water to satisfy concrete porosity. Remove free water immediately before priming.

Brush apply Ronacrete Standard Primer to the steel and allow to become tacky, not dry.

When the priming coat on steel is tacky, brush a single coat of the same primer on to the damp concrete and a second coat on to the steel. Ensure that the first priming coat applied to the steel is not removed during the application of the second coat, or scatter kiln-dried sand into the wet first coat and apply the second coat to the dry and keyed first coat.

Mixing

RonaBond HB40 Rapid must be mixed mechanically in a forced action mixer (e.g. Creteangle pan mixer) or using a high power slow speed drill (typically 500 rpm) with a paddle attachment, MR 4 or similar (do not use a free fall mixer).

Pour the dry powder into a mixing vessel containing ≥ 3 litres (but not more than 3.2 litres) of clean water. Mix for approximately 3 minutes to produce an even consistency. Note that the mix will stiffen during transit to the repair position.

Use complete packs to ensure consistency, uniform dispersion of pack contents and accuracy of powder:water ratio. To avoid a false set in warm working conditions store materials in the shade and use cool water.

Application

The mortar must be applied to the wet or tacky primer before the primer dries. If the primer dries it must be thoroughly scarified and reapplied.

Apply the mortar to reform the original profile of the concrete and cover reinforcing steel. Ensure that the mortar is fully compacted, paying particular attention to avoidance of voids around reinforcement. Layer thickness will vary according to the shape and size of the repair, the texture of the substrate and application technique. Application techniques include hand packing the mortar on to the surface.

When multiple layer application is required, each intermediate layer must be combed and allowed to harden before application of Ronacrete Standard Primer and a further layer of mortar. The repair must be finished with a steel or wood float, and may be dry sponge finished if required. If applying a protective or decorative coating such as RonaBond Crack Bridging Anti Carbonation Coating WB, RonaBond Anti-Carbonation Coating WB or RonaBond Masonry Paint WB, leaving the final layer with a sponge finish will aid adhesion.

Curing

Cure with Ronacrete Curing Membrane or tight fitting polythene as soon as possible and as quickly as is practical to prevent rapid early moisture loss from the mortar surface and minimise the risk of resultant plastic cracking. Curing is more important when working in direct sunlight and/ or in a drying breeze or wind.

Note that maximum application depth per layer is reduced and typical maximum layer thickness in larger repairs is 50mm vertically and 30mm overhead.

Test Data

• Compressive strength
• 1 hour - N/A
• 24 hours - 23N/mm²
• 7 days - 33N/mm²
• 28 days - 35N/mm²
• Tensile strength @ 28 days - 2.9N/mm²
• Flexural strength @ 28 days - 7.1N/mm²
• ISAT (ml/m²/sec) - 0.003