Method Statement for Repair of Concrete with Fosrocs Rendroc Materials

This concrete repairing method statement details the procedure for repairing the concrete works according to type of defects observed, in accordance with the manufacturer’s requirements.

The works shall be performed as mentioned in this procedure and the quality assurance requirements shall be consistent with the relevant sections of Quality Management System Manual of the contractor including the compliance with the Project Quality Plan (PQP).

This method statement describes in detail for rectifying the defect type for different types of repair as follows:

Type ID Type of Repair Proposed material Dimensions Strength of Material ( 28 days)
Type-1 Blowhole on the surface of concrete Rendroc FC   NA
Type-2 At Cracks on surface Rendroc FC Up to 3 mm 20 N/mm2
Type-3 At Bulging area after chipping Rendroc FC Up to 3 mm 70 N/mm2
Type-4 Chamfer / Edges broken Rendroc HS 10-50mm for each layer up to 150 mm thk. 70 N/mm2
Type-5 Insufficient Cover Rendroc HS 10-50mm 70 N/mm2
Type-6 Exposed Rebar Rendroc HS with Bonding agent Nitobond EP 10-50mm 70 N/mm2
Type-7 Slight Honeycomb Rendroc HS 10-50mm for each layer up to 150 mm thk. 70 N/mm2
Type-8 Honeycomb to rear of rebar Rendroc HS 10-50mm for each layer up to 150 mm thk. 70 N/mm2
Type-9 Small  voids Rendroc HS 10-50mm for each layer up to 150 mm thk. 70 N/mm2
Type-10 Void through structure Rendroc LA 20-200 mm for each layer. (Shutter required) 60 N/mm2

The filler for minor surface imperfections (up to 3 mm depth) shall be Renderoc FC – a single component, polymer modified, cementitious mortar. The material shall be capable of use without the need for an independent primer or curing system.

Overcoating with protective/decorative finishes

Renderoc FC may be overcoated with a protective /decorative coating after about 48 hours, dependent on ambient conditions. 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 parts of the structure which have not been repaired and might otherwise be at risk from the environment.

High temperature working

It is suggested that, for temperatures above 350C, the following guidelines are adopted as good working practice:

(i) Store unmixed materials in a cool (preferably temperature controlled) environment, avoiding exposure to direct sunlight.

(ii) Keep equipment cool, arranging shade protection if necessary. It is especially important to keep cool those surfaces of the equipment which will come into direct contact with the material itself.

(iii) Try to avoid application during the hottest times of the day, and in direct sunlight.

(iv) Make sufficient material, plant and labor available to ensure that application is a continuous process.

Health and Safety Requirements

Renderoc product contains cement powders which, when mixed or become damp, release alkalis which can be harmful to the skin. Nitobond AR and Nitobond SBR are slightly alkaline.

During use, avoid inhalation of dust and contact with skin and eyes. Wear suitable protective clothing, gloves, eye protection and respiratory protective equipment.

The use of barrier creams can provide additional skin protection. In case of contact with skin, rinse with plenty of clean water, then cleanse with soap and water. In case of contact with eyes, rinse immediately with plenty of clean water and seek medical advice. If swallowed, seek medical attention immediately – do not induce vomiting.

For further information, refer to the appropriate Product Material Safety Data Sheet.

Concrete Repair Method – Rendroc FC

Clean the surface and remove any dust, unsound material, plaster, oil, paint, grease, corrosion deposits or algae. Roughen the surface to remove any laitence and expose the fine aggregate by light scabbling or grit-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.

Renderoc repair mortars require no additional preparation prior to the application of Renderoc FC.

The cleaned areas should be blown clean with oil-free compressed air before continuing. All prepared areas should be thoroughly soaked with clean water immediately prior to the application of Renderoc FC. Any residual surface water should be removed prior to commencement.

Mixing – small quantities

Care should be taken to ensure that Renderoc FC is thoroughly mixed. Small quantities (up to 5 kg) can be mixed using a suitable mixing drum or bucket. Greater quantities should be mixed using a forced-action mixer. Mixing in a suitably sized drum using an approved spiral paddle attached to an approved slow speed (400/500 rpm) heavy-duty drill is an acceptable alternative.

If mixing small quantities by hand, Renderoc FC should be volume-batched. Add 3 volumes of the Renderoc FC powder (loose-filled to excess and struck off level with the top of the measuring container) to one volume of potable water. This should be mixed vigorously until fully homogeneous.

Mixing – large volumes

For larger volumes, place 3.0 litres of cool, potable water into the mixer and, with the machine in operation, add one full 10 kg bag of Renderoc FC and mix continuously for 3 to 5 minutes until fully homogeneous.

Water addition may vary slightly according to both the ambient temperature and the desired consistency of the mix, but it should not exceed 3.0 litres For additional anti-dusting, or enhanced performance properties, add 0.6 litres of Nitobond SBR to the gauging water until the desired consistency is achieved.

Note: In all cases Renderoc FC powder must be added to the water.

Application of Concrete Repairing Compound

Apply the mixed Renderoc FC to the prepared substrate, up to 3 mm thickness, by steel trowel. It should be applied with the minimum of working and be allowed to partly set before finally trowelling to a smooth finish.

If a very smooth finish is required, a small amount of water may be flicked on to the surface of the Renderoc FC with a paint brush prior to final trowelling.

Do not proceed with the application when rainfall is imminent unless in a sheltered or protected situation.


Renderoc FC is finished by striking off with a straight edge and closing with a steel or plastic float. Note that water can be drawn to the surface if ‘overworking’ with the float occurs, and an unsightly finish may result.

Damp sponges or plastic floats may be used to achieve a desired surface texture, but care should again be taken not to overwork the surface.Method Statement for Repair of Concrete with Fosrocs Rendroc Materials


Curing is not generally required. However, under extreme conditions – high temperatures and drying winds – it may be prudent to use Nitobond AR*† as a curing agent.

Nitobond AR does not require mechanical removal prior to overcoating.


Renderoc FC should be removed from tools, equipment and mixers with clean water immediately after use. Cured material can only be removed by mechanical means.

Concrete Repair Method – Rendroc HS

Shrinkage compensated, polymer modified, fiber reinforced, thixotropic repair mortar system

Renderoc HS is suitable for sprayed or troweled applications, with high build characteristics. Typical applications would include, but not be limited to, the following:

  • All types of structural repair which can be applied by trowel or wet spray.
  • Repair of structural members subjected to repetitive loading including application in trafficked areas.
  • Repairs to reinforced or pre-stressed beams or columns.
  • Repairs in industrial area, especially those containing mineral oils, lubricants etc.
  • Repairs in marine environments.

Instructions for use – Preparation

It is essential that the substrate to be repaired is sound, clean and free of all contamination. The damaged areas of concrete to be removed must be clearly identified. The Perimeter of the area should be saw cut to a depth of 10mm and the edges cut as neatly as possible keeping the sides square. Feather-edging is not permitted and a minimum thickness of 10mm must be maintained over the whole area.

The substrate should be prepared to provide a rough surface having at least a 5mm amplitude at 20mm frequency. If unsound or oil contaminated concrete is found to extend beyond the pre-marked area, consult the engineer in charge.

Subject to approval cut back to clean sound concrete. If reinforcement is corroded ensure that the back of the steel has been exposed. reinforcement should have all rust removed by the use of power tools, abrasive basting (wet or dry) or wire brushing. Reinforcing steel should be exposed and cleaned around it’s whole circumference. Steel should be prepared to Swedish Standard SIS 05-900:1967-SA2½ or BS4232 Ref. 24 second quality.

Extra protection to the reinforcement can be provided by Nitoprime Zincrich*† dependent on the circumstances of use and requirement of the client.

Severely corroded reinforcement may require replacement and the engineer must be consulted.

Water Saturation

Thoroughly saturate the surface of the concrete to provide a saturated surface dry condition. Poor quality concrete may require soaking for a significant length of time. Any surface water should be removed using an oil free compressed airjet.


Renderoc HS should be mixed mechanically with a Heavy Duty, slow speed drill or a forced action mixer fitted with Fosroc MR3 mortar mixing paddle.

Add 3 litres of water into a suitably sized mixing vessel for full bag mixing. Do not use part-bags. It is suggested that the temperature of the water should not exceed 20°C, so that the temperature of the final mixed material is not greater than 30°C. With the mixer in action, add one full bag of Renderoc HS and mix for 3-5 minutes, until the mix becomes fully homogeneous. (water levels may be adjusted to allow good spray techniques between 3 & 3.5ltrs per bag)


After mixing, Renderoc HS can be sprayed or trowel applied. Suitable spraying units are Putzmeister P11, Turbosol T20 or Meyco Deguna 20.When applying by hand, Renderoc HS, must be forced tightly into the substrate to ensure intimate contact with the pre-wetted substrate.Levelling and initial finishing should be carried using a wooden or plastic float. Final finishing should be carried out using a steel float. When the material has stiffened to the point where finger pressure lightly marks the surface, a final firm trowelling should be given using a steel float.


Renderoc HS demands good curing. Particular care is required in hot/windy conditions. Curing is to be commenced immediately either by applying a single coat Nitocote PE135, or by covering the work with plastic sheet fixed over wet hessian and taped at all edges.

Nitobond AR can be used as a curing compound but not recommended in situations where overcoating with epoxy coatings is required. However it is suitable when overcoated with the Dekguard range of protective coatings.

Repairing Concrete Method – Rendroc LA Single component free flowing low alkali micro concrete

The high fluid nature of Renderoc LA obviates the need for compaction and vibration and are most suitable for:

  • Repair zones with restricted access or congested reinforcement.
  • Reinstatement of large, strctural sections of concrete.
  • Repairs to concrete effected by alkali-silica reaction.
  • Areas where excellent chloride and carbon-di-oxide resistance is required

Renderoc LA is supplied as a ready to use blend of dry powders which requires only the site addition of clean water to produce a free-flowing, shrinkage compensated micro-concrete suitable for large volume concrete repairs at nominal thicknesses in excess of 50mm.

Renderoc LA is designed for large volume repairs typically in excess of 50mm deep. The product can be applied at sections generally upto 150 mm thick although greater thicknesses may be achievable dependent on the repair geometry. Attention to the basic design criteria given below should ensure that the full benefits of this technology are gained in use :

Water addition = 2.7 litres per 20 kg bag

Under no circumstances should part bags be used or additional water be employed. Either of these two actions will adversely affect material performance, automatically invalidating Fosroc’s standard product guarantee.

Refer attached technical guides from manufacturer.

Renderoc FC (Fairing coat)[1 component polymer modifyied cementitious

Renderoc HS (High strenght)[Shrinkage compensated, polymer modified, fibre

Renderoc LA (Low Alkali)[1 component low Alkali micro Concrete]

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