RENO C920 ST
BENEFITS
- For filling holes an cavities
- Thin-film extendable to ZERO
- Adding of sand possible
CHARACTERISTICS
- Color: grey
- Working time: 25min
- Walk on time: after 30min
- Curing time: after 10h
- Coverage: 1,6 kg/ mm/ m²
- Application thickness: 1-100mm
APPLICATION
Measure 5,5-7 liters of clean, cold water into a clean mixing bucket. Gradually add the bag of Bostik SL C920 RENO ST to the water, whilst continually mixing with an electric drill and mixing paddle until a smooth lump-free mixture is obtained. This will normally be achieved after 2 minutes.
The mixture will retain its self-smoothing capability for approximately 25 minutes under normal conditions.
Pour the mixed material onto the prepared substrate to a thickness between 1mm and 100mm.
Concrete floor repair with minimal downtime
Designed for efficient concrete floor repair, this fast-setting compound allows rapid return to service. The surface can accept foot traffic in approximately 30 minutes, while floor coverings can be installed shortly after, depending on thickness and material type.
This makes it well suited to commercial and residential environments where downtime must be kept to a minimum.
Compatible with a wide range of substrates. Including concrete, screeds, timber boards and existing tiles. RENO C920 ST offers excellent adhesion and moisture tolerance. It provides a dependable solution for both new build and renovation projects.
Repair product for multiple substrates
As part of a dependable range of concrete floor repair products, RENO C920 ST is compatible with:
- Cementitious screeds and concrete
- Existing tiles and levelling compounds
- Wooden boards (up to 3 mm application)
- Mastic asphalt screeds
- Old adhesive residues and painted surfaces (with primer where required)
Its versatility supports use across varied construction and refurbishment projects.
Concrete repair and smoothing in a single product
While not supplied as a traditional concrete repair kit, RENO C715 EASY FLASH delivers the performance expected from professional concrete repair products:
- Fast setting and curing
- Smooth, high-quality finish
- Easy mixing and application
- Strong adhesion across multiple substrates
- Minimal or no priming on most surfaces
This positions it as a versatile all-in-one solution for many repair tasks.
Application process: SL C920 RENO ST
Quick Application Steps (On-Site Guide)
- Prepare: Confirm substrate is solid, clean, dry and correctly primed
- Mix: Use 5.5–7 L of water per 25 kg bag and blend to a uniform consistency
- Apply: Place and level between 1–50 mm (up to 100 mm with aggregate)
- Wait: Allow light foot traffic after ~30 minutes
- Cover: Install floor finishes from 1 hour up to 24 hours depending on type and depth
1. Subfloor preparation
Correct preparation is critical to ensure performance:
- The base must be structurally sound, dry and free from contaminants such as oil, grease or dust
- Mechanically remove laitance, weak layers, old adhesives and surface coatings
- Thoroughly vacuum all loose debris before application
- Ensure existing tiles are secure; re-fix or remove where necessary
- Smooth or dense surfaces must be abraded and degreased prior to use
- Cracks and joints should be repaired using suitable systems before levelling
- Always apply an appropriate primer based on substrate type
All substrates should meet local regulations and site standards prior to installation.
2. Mixing
- Pour 5.5 to 7 litres of clean, cold water into a mixing vessel
- Slowly introduce the 25 kg powder while mixing with a drill and paddle
- Continue mixing for around 2 minutes until a smooth, lump-free mortar is achieved
- No resting (slake) time is required due to rapid-setting formulation
- Pot life: approximately 10 minutes
Important: Excess water will weaken the mix and negatively impact strength and durability.
3. Application
- Apply in a single layer from 1–50 mm; extendable up to 100 mm when bulked with sand
- Pour or place the material directly onto the prepared area
- Compact firmly and spread evenly using a trowel to the required profile
- Finish and trim within ~10 minutes before initial set occurs
- For deeper repairs, bulk with suitable aggregate (e.g. quartz sand)
- Allow curing before applying additional layers, re-priming where required
Designed for heavy-duty repairs, including filling voids, reshaping steps and forming falls.
4. Drying & curing
- Working time: ~10 minutes
- Walk-on time: ~30 minutes
Avoid rapid drying by protecting from draughts and direct sunlight.
Typical covering times (≤50 mm):
- Ceramic tiles: ~1–3 hours
- PVC / carpet: ~2–5 hours
- Wood, rubber, coatings: ~12–24 hours
- Thicknesses above 50 mm: allow ~24 hours
5. Underfloor heating
- Turn off heating systems 48 hours before, during, and at least 48 hours after installation
- Once cured, gradually reintroduce heat to operating temperature
Common mistakes to avoid
- Adding too much water, reducing mechanical strength
- Mixing excessive quantities despite short working time (~10 minutes)
- Applying onto poorly prepared or contaminated substrates
- Failing to prime appropriately for the substrate
- Not accounting for thickness limits or bulking requirements
- Exposure to extreme temperatures outside +15°C to +30°C
- Allowing rapid drying due to airflow or direct sunlight
Frequently Asked Questions
Damaged mortar, holes and surface imperfections can be repaired with different products depending on the repair depth and finish required. RENO C715 EASY FLASH is described as a rapid drying patching and smoothing compound for internal repairs on walls and floors. RENO G905 ALPHA ST is recommended for repair, patching and smoothing surface imperfections. RENO C950 QUICK and RENO C920 ST are recommended for deep or large repairs in a single layer.
Application thickness varies by product. RENO C715 EASY FLASH is suitable from feather edge, with the TDS describing the product as suitable up to 15 mm in the description and listing feather edge to 10 mm in the product characteristics table. RENO G905 ALPHA ST is 1 to 10 mm. RENO C950 QUICK is 1 to 50 mm in one layer. RENO C920 ST is 1 to 50 mm unextended and 50 to 100 mm extended. RENO C970 PLUS is 1 to 100 mm.
For repairing damaged areas or filling holes, use a repair mortar such as RENO C950 QUICK or RENO C920 ST. These products are suitable for applications from approximately 1 to 50 mm (or up to 100 mm depending on the product and extension), depending on substrate condition and preparation.
Repair mortar is applied onto a prepared surface using a trowel. Pour or place the mixed mortar into the damaged area, spread evenly to the desired thickness, and smooth the surface before the material starts to set. Products such as RENO C950 QUICK and RENO C920 ST allow shaping, filling and reprofiling of surfaces.
RENO C950 QUICK is a fast-setting repair mortar suitable for applications up to 50 mm and is walkable after about 45 minutes. RENO C920 ST can be applied up to 100 mm when extended and has a faster walk-on time of about 30 minutes. C920 ST is better suited for deeper or more demanding repairs.
Holes and damaged areas can be filled with repair mortars according to the required build. RENO C950 QUICK is recommended for deep or large repairs in a single layer with an application thickness of 1 to 50 mm. RENO C920 ST is recommended for deep or large repairs with an application thickness of 1 to 50 mm unextended and 50 to 100 mm extended. For minor internal repairs and smoothing, RENO C715 EASY FLASH is a rapid drying patching and smoothing compound suitable from feather edge.
Repair mortars are used to restore damaged concrete or masonry surfaces. The brochure states that they provide strength, durability and a smooth finish, and that they allow professionals to fill cracks, level surfaces and reinforce structures.
The brochure states that repair mortars can be used for stair repair, shaping slopes, chase filling, crack bridging and concrete repair. The TDS also support filling holes, reprofiling stairs, reshaping slopes and surface levelling, depending on product.
The brochure states that repair mortars provide strength, durability and a smooth finish. In renovation, they are positioned to restore damaged surfaces and support long-lasting performance.
Repair mortars must be mixed with clean water using the ratios specified per product. RENO C950 QUICK uses 5 to 6 litres of water per 25 kg bag, RENO C920 ST uses 5.5 to 7 litres per 25 kg bag, and RENO G905 ALPHA ST uses 8 litres per 20 kg bag. Mix using an electric drill and paddle until a smooth, lump-free consistency is achieved.
Drying time depends on the product and thickness. RENO C950 QUICK is walkable after 45 minutes, with floor coverings from 1 to 24 hours depending on type. RENO C920 ST is walkable after 30 minutes, with coverings from 1 to 24 hours. RENO G905 ALPHA ST is walkable after 2 to 3 hours, with full curing from 24 hours depending on thickness.
Consumption depends on the product and thickness. RENO G905 ALPHA ST uses approximately 1.1 kg per mm per square metre. RENO C950 QUICK and RENO C920 ST use approximately 1.6 kg per mm per square metre. RENO C970 PLUS uses approximately 1.5 kg per mm per square metre.
A damaged subfloor can be repaired using repair mortars and reinforcement systems. RENO G905 ALPHA ST is suitable for patching and levelling imperfections. RENO C950 QUICK or RENO C920 ST can be used to fill holes, reshape surfaces and restore the subfloor. For weak subfloors, RENO U550 REINFORCE helps stabilise and distribute loads.
Walk-on time depends on the product. RENO P520 EASY is walkable after about 30 minutes. RENO C920 ST is walkable after about 30 minutes. RENO C950 QUICK is walkable after about 45 minutes. RENO G905 ALPHA ST is walkable after about 2 to 3 hours.
