Fosroc Renderoc CF
A single-part, non-shrink cementitious filler that seals cracks up to 20 mm wide in plaster, masonry and concrete, and stays put on vertical and overhead faces.
What is it?
A ready-to-use, single-component cementitious crack filler that you mix with clean water on site. It is non-shrink, non-sag and hydrophobic, so it seals static cracks without slumping or pulling away as it cures.
Where is it used?
Non-structural crack sealing on plaster, masonry and concrete surfaces, indoors and in exposed external conditions, across walls, columns, soffits and parapets.
Why use it?
It fills cracks up to 20 mm in a single, honest operation, resists water ingress, and takes common paints and coatings once cured, so patched areas disappear into the finish.
How is it applied?
Cut a shallow V-groove along the crack, clean and pre-wet it, then press the mixed mortar in with a trowel or putty blade and finish flush with a damp sponge.
About Fosroc Renderoc CF
Fosroc Renderoc CF is one of those quietly useful products every repair contractor ends up keeping on the shelf. It is a single-part, non-shrink cementitious crack filler that arrives as a dry powder and needs only clean water to become a workable mortar. Its job is narrow and it does it well: sealing cracks in plaster, masonry and concrete, up to 20 mm wide, without the shrinkage and re-cracking that plague ordinary cement-sand mixes and cheap fillers. Because it is formulated to be non-sag, it holds its shape on vertical walls and even overhead soffits, so you are not fighting gravity while you tool the surface flush.
What makes it easy to live with on site is that it behaves predictably. It sets quickly enough to keep a repair sequence moving, finishes cleanly with a putty blade or a damp sponge, and accepts the common decorative paints and protective coatings applied afterwards. The hydrophobic character of the cured filler helps keep water out of the sealed crack, which matters on external elevations and wet areas where a filled crack that later wicks moisture simply reopens the problem. Renderoc CF is a cosmetic-to-minor repair material, not a structural mortar, and used within that brief it gives a durable, paintable result that holds up in Indian weather.
The technical insight
The value of Renderoc CF lies in how a factory blend of cement, graded fillers and chemical additives is tuned to defeat the two failure modes of a filled crack: drying shrinkage and water re-entry. A naive cement-sand plug shrinks as it cures and debonds from the crack walls, leaving a hairline gap that reopens the crack path. Renderoc CF is engineered to be non-shrink, so the set mortar stays keyed against the substrate rather than pulling away. The thixotropic, non-sag rheology means the fresh mortar has enough internal structure to resist slumping out of an overhead or vertical crack yet still trowels smoothly under pressure. Layered on top of that is a hydrophobic modification that reduces capillary water uptake into the cured filler, so a sealed external crack does not quietly soak, freeze-thaw or carbonate its way back open. The result is a repair that bonds, stays dimensionally stable, sheds water and presents a sound, paintable face for the finishing system that follows.
Where it is used
- Sealing shrinkage and settlement cracks in internal and external plaster
- Filling cracks in brick, block and stone masonry before painting
- Repairing static (non-moving) cracks in concrete walls, columns and beams
- Overhead and vertical crack sealing on soffits, lintels and parapets
- Making good hairline-to-wide cracks up to 20 mm ahead of a decorative finish
- Sealing cracks on external elevations exposed to rain and weathering
- Preparing cracked substrates for waterproof coatings and texture paints
- Cosmetic crack rectification on facades, boundary walls and staircases
Key advantages
- Single-component powder that needs only clean water on site, removing mixing-ratio guesswork
- Non-shrink formulation that stays keyed to the crack walls instead of pulling away
- Non-sag consistency lets it be used on horizontal, vertical and overhead cracks
- Hydrophobic character resists water ingress into the sealed crack on external faces
- Handles a wide crack range in one product, up to 20 mm width
- Finishes smoothly with a putty blade or damp sponge for a paint-ready surface
- Sets quickly, keeping repair and painting sequences moving on schedule
- Over-coatable with common decorative paints and protective coatings once cured
Limitations & considerations
- It is a crack filler for cosmetic and minor repair only, not a structural repair mortar
- Suited to static cracks; it will not accommodate live, moving or thermally cycling joints
- The 20 mm width limit means very wide spalls or deep patches need a repair mortar instead
- Genuinely moving joints require a flexible sealant, not a rigid cementitious filler
- Performance depends on proper V-groove cutting, cleaning and pre-wetting of the crack
- Fast set gives limited working time, so mix only what can be placed and tooled promptly
Selection & best practice
Treat crack preparation as most of the job. Open the crack into a shallow V-groove, roughly 6 mm by 6 mm, using a saw cut or chisel, then clean out all loose material, laitance and dust so the filler bonds to sound substrate rather than debris. Dampen the groove with clean water to a saturated surface-dry condition just before filling; a dry, dusty crack draws water out of the mortar and weakens the bond. Mix only the quantity you can place before the material starts to stiffen, and press it firmly into the full depth of the groove to avoid trapping air pockets, working from the back of the crack outward. Tool the surface flush and finish with a putty blade or damp sponge for a clean, paintable face. On external elevations, allow the filler to cure fully before over-coating, and pair it with a suitable waterproof or protective coating so the sealed crack is defended against rain and weathering.
Specifications
| Product type | Single-part, non-shrink cementitious crack filler |
| Composition | Cement, graded fillers and chemical additives (powder) |
| Mixing | Site addition of clean water only |
| Suitable substrates | Plaster, masonry and concrete |
| Maximum crack width | Up to 20 mm |
| Application orientation | Horizontal, vertical and overhead (non-sag) |
| Water resistance | Hydrophobic, resists water ingress |
| Finish / over-coating | Over-coatable with common paints and coatings |
Industry use cases
Residential & Commercial Buildings
Sealing plaster and masonry cracks on internal and external walls before repainting, so hairline and settlement cracks do not telegraph back through the fresh finish.
Facade & Elevation Maintenance
Rectifying weathering cracks on external elevations, parapets and boundary walls where the hydrophobic, non-sag filler keeps rainwater out of vertical and overhead cracks.
Repainting & Refurbishment Contractors
A fast, paint-ready crack-filling step in maintenance repaint cycles, letting crews seal and finish cracks and move straight to the coating system.
Institutional & Public Infrastructure
Cosmetic crack sealing on schools, hospitals and public buildings, on staircases, soffits and lintels, ahead of protective decorative finishes.
Frequently asked questions
Is Renderoc CF a structural repair material?
What crack width can it handle?
Can it be used on ceilings and overhead surfaces?
Do I need a primer before filling?
Can it be painted over?
Does Space Arc supply Renderoc CF across India and provide technical support?
How we position Fosroc Renderoc CF
Renderoc CF sits at the light-repair end of Fosroc’s Renderoc concrete-repair range: it is a crack filler for cosmetic and minor cracks, not a structural mortar. When a crack turns out to be a spall, a wider defect or a section that needs rebuilding beyond the 20 mm limit, step up to a Fosroc repair mortar such as Renderoc CS for thick-layer restoration, or to Renderoc FC for fine cosmetic infilling of blowholes and honeycombing in formed concrete. Where the real problem is an active, fountaining water leak rather than a static crack, reach for the rapid-setting Fosroc Renderoc Plug. Genuinely moving joints, by contrast, are outside the remit of any rigid cementitious filler and call for a flexible sealant, we can specify an appropriate joint sealant from our Fosroc or other brand ranges. For the best long-term result on external elevations, we typically pair Renderoc CF with a Fosroc primer and a protective or waterproof coating so the sealed crack stays defended against rain and weathering.
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