Concrete Repair Mortars

Renderoc HB40

High performance medium-weight concrete reinstatement mortar.


For the reinstatement of reinforced concrete where low permeability characteristics are required and where higher compressive strength is a consideration. Renderoc HB40 has been engineered for the repair of columns and beams but, because of its relatively low fresh wet density, is also suitable for soffit repairs. Where compatibility with lower strength concrete is required, Renderoc HB25 should be used.


  • Maximum compatibility with concrete of compressive strength greater than 30 N/mm²
  • High-build applications possible while maintaining higher compressive strengths — fewer cold joints
  • Frequently obviates the need for formwork
  • Polymer-modification provides extremely low permeability to water, carbon dioxide and chlorides
  • Exceptional system of shrinkage compensation provides long-term dimensional stability
  • Can be applied quickly and efficiently by wet spraying
  • One component, pre-bagged to overcome site batched variations
  • Contains no chloride admixtures
  • Renderoc Galvashield XP compatible


Renderoc HB40 concrete reinstatement mortar is supplied as a ready to use blend of dry powders which requires only the site addition of clean water to produce a highly consistent, medium-weight repair mortar. It gives good handling characteristics while minimising water demand.

The low water requirement ensures good strength gain and long-term durability. Renderoc HB40 is designed to achieve maximum compatibility with concrete with a compressive strength greater than 30 N/mm². Where strengths below 30 N/mm² and/or higher builds are required, Renderoc HB25 should be used.

Standards compliance:

Renderoc HB40 has been approved by the British Board of Agrément, Certificate No. 98/3461. Renderoc HB40 has been tested and approved in accordance with the Hong Kong Housing Authority Specification TM1 to TM8 (1990).


The following results were obtained at a water: powder ratio of 0.15 and a temperature of 20°C unless otherwise stated.

Test method Typical result:

Compressive strength 16 N/mm2 @ 1 day
(BS 6319 Pt 2: 1983 — 30 N/mm2 @ 3 days
dry cure): 40 N/mm2 @ 7 days
44 N/mm2 @ 28 days
Flexural strength 6.9 N/mm2 @ 28 days (BS 6319 Pt 3: 1990):
Tensile strength 2.9 N/mm2 @ 28 days (BS 6319 Pt 7: 1985):
Modulus of elasticity in 18.4 kN/mm2 @ 28 days compression (BS 6319 Pt 6: 1984):
Water absorption
ISAT (BS 1881 Pt 5: 1970) — 10 minutes: 0.006 ml/m2/sec -2 hours: 0.002 ml/m2/sec
Drying shrinkage < 300 microstrain 27°C/RH55%: @ 7 days
Carbon dioxide barrier 600 mm equivalent thickness of concrete to Renderoc HB40 @ 10 mm (Taywood method):
Chloride diffusion - < 5 x 10–13 m2 s–1 Taywood bulk diffusion (low permeability concrete test (accelerated): concrete defined as < 1 x 10–12 m2 s–1 by non accelerated testing) Coefficient of thermal 11.3 x 10–6/°C expansion:
Setting time (BS 4551 Pt 14: 1980) —
Initial set: 3 hours
Final set: 5 hours
Fire rating Non combustible
(BS 476 Pt 4: 1970): (Class 0 surface)
Fresh wet density: Approximately 1840 kg/m3 dependent on actual consistency used
Chemical resistance: The low permeability of Renderoc HB40 severely retards chemical attack in aggressive environments. The cured mortar is highly impermeable to acid gases, water-borne chloride ions, and oxygen

Application instructions:


Saw cut the edge of the repair to a depth of at least 10 mm. Break out the complete repair area to a minimum depth of 10 mm up to the sawn edge. Clean the surface and remove any contamination. Where breaking out is not required, roughen the surface and remove any laitance by light scabbling or abrasive blasting.

Oil and grease deposits should be removed by steam cleaning, detergent scrubbing or the use of a proprietary degreaser. The effectiveness of decontamination should then be assessed by a pull-off test.

Expose fully any corroded steel in the repair area and remove all loose scale and corrosion deposits. Steel should be cleaned to a bright condition paying particular attention to the back of exposed steel bars. Abrasive blasting is recommended for this process.

Where corrosion has occurred due to the presence of chlorides, the steel should be high-pressure washed with clean water immediately after abrasive-blasting to remove corrosion products from pits and imperfections within its surface.

Reinforcing steel priming:

Apply one full coat of Nitoprime Zincrich Plus and allow to dry before continuing. If any doubt exists about having achieved an unbroken coating, a second application should be made and, again, allowed to dry before continuing.

Substrate priming:

The substrate should be saturated surface dry immediately before the application of the primer i.e. it should be thoroughly saturated with clean water and any residual surface water removed prior to applying one coat of Nitobond HAR primer and scrubbing it well into the surface. Under severe drying conditions repeated soaking may be necessary to ensure the substrate is still saturated at the time of application of the primer.

Renderoc HB40 can be applied as soon as the primer becomes tacky. If the Nitobond HAR is too wet, overhead and vertical build up of the Renderoc HB40 mortar may be difficult.

In exceptional circumstances, e.g. where a substrate/ repair barrier is required or where the substrate is wet or likely to remain permanently damp, Nitobond EP should be used. Contact the local Fosroc office for further information.


Care should be taken to ensure that Renderoc HB40 is thoroughly mixed. A forced-action mixer is essential.

Mixing in a suitably sized drum using an approved Renderoc Spiral Paddle in a slow speed (400/500 rpm) heavy-duty drill is acceptable for the occasional one-bag mix. Free-fall mixers must not be used. Mixing of part bags should never be attempted. For normal applications, place 3.75 to 4.0 litres of drinking quality water into the mixer and, with the machine in operation, add one full 25 kg bag of Renderoc HB40 and mix for a minimum of 3 minutes to a maximum of 5 minutes until fully homogeneous. Note that the powder must always be added to the water.

Mixing warning:

As with other ‘one pack’ repair mortars, Renderoc HB40 may exhibit satisfactory handling characteristics even though inadequately mixed. This will result in a significantly lower level of performance or possible failure.

Mixing instructions must be strictly adhered to with particular emphasis on the quantity of water used and the time of the mixing operation.


Exposed steel reinforcing bars should be firmly secured to avoid movement during the application process as this will affect mortar compaction, build and bond. Apply the mixed Renderoc HB40 to the prepared substrate by gloved hand or trowel. Thoroughly compact the mortar on to the primed substrate and around the exposed reinforcement. Renderoc HB40 can be applied in sections up to 40 mm thickness in vertical locations and up to 30 mm thickness in overhead locations in a single application and without the use of formwork. Thicker sections should be built-up in layers but are sometimes possible in a single application dependent on the actual configuration of the repair area and the volume of exposed reinforcing steel.

If sagging occurs during application, the Renderoc HB40 should be completely removed and reapplied at a reduced thickness on to the correctly reprimed substrate.

Note: the minimum applied thickness of Renderoc HB40 is 10 mm.


Additional build-up can be achieved by application of multiple layers. The final thickness is dependent on the material consistency and substrate profile.

The surface of the intermediate layers should be comb scratch-keyed and cured with Nitobond AR. Repriming with Nitobond HAR and a further application of Renderoc HB40 may proceed as soon as this layer has set.

Spray application:

Renderoc HB40 can be quickly and efficiently applied by the wet spray technique. Where large areas of repair are required, the rapid placement and higher build attainable offer economic advantages. Typical achievable thicknesses are 70 - 110 mm vertically and 60 - 85 mm overhead. The resultant repair is more dense with enhanced mortar/substrate bond characteristics. For further details on wet spray techniques contact the local Fosroc office.


Renderoc HB40 is finished by striking off with a straight edge and closing with a steel float. Wooden or plastic floats, or damp sponges may be used to achieve the desired surface texture.

The completed surface should not be overworked. After spray application, the mortar may need to be ‘cut back’ to the required profile using a steel float and then finished with damp sponges as described above.

Low temperature working :

In cold conditions down to 5°C, the use of warm mixing water (up to 30°C) is advisable to accelerate strength development. Normal precautions for winter working with cementitious materials should then be adopted. The material should not be applied when the substrate and/or air temperature is 5°C and falling. At 5°C static temperature or at 5°C and rising, the application may proceed.

High temperature working:

At ambient temperatures above 35°C, the material should be stored in the shade and cool water used for mixing.


Renderoc HB40 is a cement-based repair mortar. In common with all cementitious materials, it must be cured.

Immediately after finishing, Nitobond AR should be sprayed on to the surface of the finished mortar in a continuous film.

Large areas should be cured as trowelling progresses (0.5 m² at a time) without waiting for completion of the entire area.

In fast drying conditions, supplementary curing with polythene sheeting taped down at the edges must be used. In cold conditions, the finished repair must be protected from freezing.

Overcoating with protective decorative finishes:

To limit the advance of chlorides and carbon dioxide, Fosroc recommend the use of the Dekguard* range of protective, anti-carbonation coatings. These products provide a decorative and uniform appearance as well as protecting areas of the structure which might otherwise be at risk from the environment. Dekguard products may be applied over the repair area without prior removal of the Nitobond AR curing membrane. Other curing membranes must be removed prior to the application of Dekguard products.


Nitobond HAR, Nitobond AR and Renderoc HB40 should be removed from tools, equipment and mixers with clean water immediately after use. Cured material can only be removed mechanically. Equipment used with Nitoprime Zincrich Plus and Nitobond EP should be cleaned with Fosroc Solvent 102*.


Renderoc HB40: 25 kg bags
Nitoprime Zincrich Plus: 1.9 litre and 800 ml cans
Nitobond HAR: 5 and 25 litre drums
Nitobond AR: 5 and 25 litre drums
Fosroc Solvent 102: 5 and 25 litre tins

Coverage and yield:
Renderoc HB40: Approximately 15.75 litres /
25 kg bag (approximately
1.5 m² at 10 mm thickness)
Nitoprime Zincrich Plus: 8 m2/litre
Nitobond AR: 6 - 8 m2/ litre
Nitobond HAR: 3 - 4 m2/ litre
Notes: the actual yield per bag of Renderoc HB40 will depend on the consistency used. The yield will be reduced if the material is applied by a spray technique.

Renderoc HB40 should not be used when the temperature is below 5°C and falling. Do not mix part bags. Due to the relatively lightweight nature of Renderoc HB40, the product should not be used in areas subjected to traffic (in these circumstances, Renderoc S should be considered).
It should not be exposed to moving water during application. Exposure to heavy rainfall prior to the final set may result in surface scour. If any doubts arise concerning temperature or substrate conditions, consult the local Fosroc office.

The product has a shelf life of 12 months from the date of manufacture if kept in dry storage in the original, unopened bags. If stored at high temperatures and/or high humidity conditions the shelf life may be reduced to less than 6 months. Nitobond HAR and Nitobond AR should be protected from frost.


Health and safety:
Please refer to appropriate Product Safety Data Sheet for further information.

Renderoc HB40 is non-flammable.
For further information, refer to Product Safety Data Sheet.
Nitoprime Zincrich Plus and Fosroc Solvent 102: are flammable. Keep away from sources of ignition. No Smoking. In the event of fire, extinguish with CO2 or foam.
Do not use a water jet.

Flash points:
Nitoprime Zincrich Plus: 41°C
Fosroc Solvent 102: 33°C

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