Fosroc Renderoc BF2
Two-component polymer-modified cementitious blow hole filler and fairing coat for reprofiling concrete imperfections from 0 to 10 mm prior to protective coating.
What is it?
A two-component, polymer-modified cementitious blow hole filler supplied as a pre-blended dry powder with a matched gauging liquid, mixed on site to a smooth fairing-coat mortar.
Where is it used?
Applied to vertical and overhead concrete and masonry surfaces to fill blow holes, surface pinholes and shrinkage cracks, and to reprofile large areas — typically as a final fairing coat before applying a Dekguard or other protective/anti-carbonation coating.
Why use it?
It blocks the blow holes and surface voids that would otherwise cause pinholing and poor film build in a protective coating, giving a dense, closed surface with excellent bond and thermal compatibility, without needing a separate primer or curing agent.
How is it applied?
Saturate the prepared, pre-soaked substrate, mix powder into liquid at a 1:0.3 by weight (3:1 by volume) ratio, apply 0–10 mm thick by steel trowel, let it partly set, then trowel to a smooth finish; overcoat after 48 hours.
About Fosroc Renderoc BF2
Fosroc Renderoc BF2 is a two-component, polymer-modified cementitious blow hole filler that sits within Fosroc’s wider Renderoc concrete-repair family. Unlike the structural repair mortars in that range, BF2 is purpose-built for the cosmetic-but-critical final stage of a repair or refurbishment: closing the blow holes, bug holes, pinholes and shallow surface defects that are inherent to formed concrete. Left unfilled, these voids trap air and cause pinholing, poor adhesion and uneven film build when a protective or decorative coating is later applied. BF2 is supplied as a ready-to-use blend of dry powders that requires only the site addition of its matched gauging liquid to produce a consistent, easily worked mortar — a deliberate design choice that removes batching guesswork and makes the product practical for remote sites where measuring water accurately is difficult. It is intended for application in the 0 to 10 mm thickness band on vertical and overhead surfaces, and is fully compatible with other Renderoc mortars and with Dekguard protective coatings, so it integrates cleanly into a complete Fosroc repair-and-protect specification. For Indian contractors and consultants, BF2 occupies the niche between deep-section repair (handled by the heavier Renderoc mortars) and the protective coating itself, acting as the fairing coat that determines how good the finished, coated surface ultimately looks and performs.
The technical insight
The defining technical feature of Renderoc BF2 is its low average linear coefficient of thermal expansion — approximately 4.7 x 10⁻⁶ per °C over the 23–100°C range — which is close to that of host concrete. This thermal compatibility is what allows a thin 0–10 mm fairing layer to remain bonded under the daily and seasonal temperature swings typical of Indian facades and structures, rather than debonding or crazing the way a thermally mismatched filler would. The powder-to-liquid ratio is fixed at 1:0.3 by weight (3:1 by volume), and Fosroc explicitly supports part-mixing at this volumetric ratio so a crew can mix only what they will use within the working life — useful because that working life is temperature-sensitive: about 45 minutes at 20°C but only around 20 minutes at 35°C, with setting time (to BS 5075) of roughly 60 minutes at 20°C falling to 45 minutes at 35°C. Fresh wet density is about 1750 kg/m³, reflecting a deliberately light, easily troweled mortar rather than a high-density structural repair material. Because it is polymer-modified, BF2 develops its bond and thermal stability without an independent bonding primer; the polymer also gives the closed, low-permeability surface needed for a sound coating substrate. Note that BF2 is a finishing and reprofiling material — it is not a load-bearing structural repair mortar and should be specified as the fairing/blow-hole stage, not as a substitute for full-depth patch repair.
Where it is used
- Filling blow holes, bug holes and surface pinholes in formed concrete prior to overcoating with a protective or anti-carbonation system
- Filling fine shrinkage cracks and shallow surface imperfections in concrete
- General reprofiling and fairing of large concrete areas to achieve a uniform, coatable surface
- Reprofiling used in association with deeper Renderoc repair mortars as the final smoothing/finishing coat
- Surface preparation of vertical and overhead concrete elements ahead of Dekguard and similar decorative/protective coatings
- Cosmetic finishing of refurbished facades, soffits, columns and structural elements during repair and rehabilitation projects
Key advantages
- No independent primer or curing agent normally required, saving time and cost on site
- Supplied with a matched gauging liquid, eliminating water-batching errors and making it suitable for remote locations
- Excellent bond to the concrete substrate
- Low thermal expansion (~4.7 x 10⁻⁶ /°C) giving good thermal compatibility with host concrete
- Part-mixing permitted at the fixed 3:1 volume ratio, so crews mix only what they can use within the working life
- Fully compatible with other Renderoc mortars and Dekguard protective coatings for a single-source specification
- Light, easily troweled mortar suitable for vertical and overhead application
- Non-flammable product
Limitations & considerations
- Limited to a 0 to 10 mm thickness band — not a deep-section or structural repair mortar
- Should not be used when the temperature is below 5°C and falling
- Working life shortens sharply with heat — roughly 45 min at 20°C but only about 20 min at 35°C — demanding faster placement in Indian summer conditions
- Above 35°C ambient, components must be kept in air-conditioned storage below 25°C and special procedures followed
- Do not apply when rainfall is imminent unless in a sheltered or protected situation
- If subject to water immersion, requires a minimum 7-day cure at 25°C; permanent immersion may cause a colour change (barrier properties unaffected)
- Overcoating only after 48 hours and at up to 75% relative humidity, depending on coating type
- Contains cement powders that release harmful alkalis when damp — PPE required
Selection & best practice
Always treat Renderoc BF2 as the final fairing stage, not the structural one: complete any deep patch repairs with the appropriate Renderoc mortar first, then prepare the surface by removing laitance, dust, oil and unsound material and thoroughly soaking the substrate with clean water, removing residual surface water before application. Add powder to liquid (never the reverse) and mix 3–5 minutes with a slow-speed (400–500 rpm) heavy-duty drill and Fosroc mortar paddle to a fully homogeneous paste; in hot Indian conditions, batch only what can be placed within the shortened working life and consider pre-chilling components. Apply 0–10 mm by steel trowel with minimum working, let it partly set, then trowel smooth — flicking a little water on with a brush before final trowelling if a very smooth finish is needed. Curing is normally unnecessary, but under high temperatures and drying winds protect the surface with Nitobond AR or taped-down polythene. Overcoat only after 48 hours, and run a small site trial over a representative area to confirm coverage before ordering in bulk.
Specifications
| Product type | Two-component polymer-modified cementitious blow hole filler / fairing coat |
| Application thickness | 0 to 10 mm |
| Powder : liquid mix ratio | 1:0.3 by weight (3:1 by volume) |
| Working life (approx.) | ~45 min @ 20°C; ~20 min @ 35°C |
| Setting time (BS 5075) | ~60 min @ 20°C; ~45 min @ 35°C |
| Fresh wet density | 1750 kg/m³ |
| Coefficient of thermal expansion (23–100°C) | 4.7 x 10⁻⁶ per °C |
| Pack supply | 16.66 kg powder + 5 litre liquid (21.66 kg pack) |
| Yield | 12.4 litres per 21.66 kg pack |
| Overcoating time | After 48 hours, up to 75% relative humidity (coating dependent) |
| Minimum application temperature | 5°C and rising (do not use below 5°C and falling) |
| Water-immersion cure | Minimum 7 days @ 25°C if immersed |
| Shelf life | 12 months in dry store, unopened @ 25°C (4–6 months in hot/humid conditions) |
| Fire rating | Non-flammable |
Industry use cases
Bridge & infrastructure rehabilitation
Fairing coat over repaired concrete piers, soffits and parapets to close blow holes before applying an anti-carbonation Dekguard coating, ensuring a pinhole-free protective film.
Water-retaining & marine structures
Reprofiling and blow-hole filling on tanks, reservoirs and coastal RCC, with a minimum 7-day cure where water immersion is expected; note permanent immersion may cause a cosmetic colour change only.
Commercial & residential facade refurbishment
Smoothing and reprofiling spalled or honeycombed concrete columns, beams and slabs on building exteriors prior to decorative protective coatings.
Industrial plants & precast
Finishing formed concrete elements and precast units where bug holes and surface voids must be filled before coating or before achieving an architectural fair-faced appearance.
Car parks & multi-storey decks
Used with other Renderoc mortars as the final fairing layer on overhead and vertical surfaces ahead of protective deck and soffit coating systems.
Frequently asked questions
Is Fosroc Renderoc BF2 a structural repair mortar?
What is the mixing ratio and how is it batched on site?
How much area does one pack cover?
Does Renderoc BF2 need a separate primer or curing agent?
How soon can it be overcoated, and is it compatible with Fosroc coatings?
What precautions apply in hot Indian site conditions?
How we position Fosroc Renderoc BF2
Within the Fosroc system, Renderoc BF2 is the dedicated blow-hole-filling and fairing stage that completes a repair before protection. It pairs naturally with the structural Renderoc repair mortars (which handle full-depth patch repair) and with Dekguard anti-carbonation and decorative coatings (which it is formulated to receive), and Nitobond AR is its recommended curing aid under harsh drying conditions. It is closely related to Fosroc’s single-component Renderoc BF, with BF2 being the two-component version that ships with a matched gauging liquid for consistent on-site mixing in remote locations. For specifiers comparing brands in India, credible equivalents in the blow-hole-filler / fairing-coat niche include Sika’s MonoTop and Sika fairing-coat products, MBS (MYK)/MYK Schomburg cementitious fairing mortars, Dr. Fixit’s repair-and-reprofiling range, and STP/Sika-style surface levelling mortars. BF2’s particular strengths in this comparison are its supplied gauging liquid that removes water-batching error, its part-mixing allowance, and its tight integration with the rest of the Renderoc-plus-Dekguard repair-and-protect specification — making it the logical choice when the surrounding system is already Fosroc. As an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, Space Arc Engineering can supply BF2 alongside the matching primers, structural mortars and protective coatings for a single-source repair specification.
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