Self Leveling Concrete: UK Guide
Quick summary
Self leveling concrete is a cement-based mix with fine aggregates designed for depths of 10-50mm. Used for structural floor repairs, garage floors, outdoor slabs, and industrial applications. Flows to self-level but sets harder and stronger than standard self leveling compound. Suitable for exterior use. Costs £10-18 per 25kg bag.
What is self leveling concrete?
Self leveling concrete (SLC) is a cementitious mix containing fine aggregates (sand or graded stone) and flow-enhancing polymers. It is designed for thicker applications (10-50mm) than standard self leveling compound. The mix flows to find its own level but cures to a strong, durable surface suitable for structural loads and outdoor use.
It differs from traditional concrete in two ways. First, it flows rather than needing spreading and trowelling. Second, it works at shallower depths (traditional concrete screeds need 50mm+ for strength). The polymer additives improve flow, adhesion, and crack resistance.
Common UK products include Sikagard Self Leveling Concrete, Ronacrete Flexcrete SLC, and Larsen Fast Floor. These are contractor-grade products sold through specialist merchants.
Self leveling concrete vs self leveling compound
| Aspect | Self Leveling Compound | Self Leveling Concrete |
|---|---|---|
| Typical depth | 3-10mm | 10-50mm |
| Aggregate | None or very fine filler | Fine sand or graded aggregate |
| Strength | 20-30 MPa compressive | 30-50 MPa compressive |
| Use location | Interior only | Interior and exterior |
| Surface finish | Smooth (suitable for vinyl, laminate) | Slightly textured (suitable for tiles, coating) |
| Cost | £6-12 per 20kg bag | £10-18 per 25kg bag |
Use self leveling compound for thin smoothing layers indoors before flooring. Use self leveling concrete for thicker structural repairs, outdoor areas, or industrial floors.
When to use self leveling concrete
Garage and workshop floors
Repair cracked, uneven, or damaged concrete floors. Pour at 15-30mm depth to level and strengthen the surface. Suitable for vehicle traffic once fully cured. Apply a resin coating or epoxy paint for durability and easy cleaning.
Outdoor patios and paths
Level sunken or uneven exterior slabs. Use exterior-grade self leveling concrete designed to resist freeze-thaw cycles. Apply at 10-25mm depth. Ensure adequate drainage and follow manufacturer's curing instructions for outdoor use.
Industrial and commercial floors
Warehouses, factories, and retail spaces need flat, strong floors for racking, machinery, or foot traffic. Self leveling concrete at 25-50mm depth provides a durable, level surface ready for resin coating or polished finish.
Ramps and access areas
Create shallow slopes or repair damaged ramp surfaces. Self leveling concrete flows to the correct profile and sets hard enough for wheelchair access or trolley traffic.
When not to use it
For depths over 50mm, use traditional concrete screed (more economical). For thin indoor smoothing (under 10mm), use standard self leveling compound (finer finish). For structural slabs from scratch, use ready-mix concrete.
Application depth and coverage
Self leveling concrete is designed for 10-50mm depth. Below 10mm it lacks strength and may delaminate. Above 50mm it becomes uneconomical (use traditional screed instead).
Coverage per 25kg bag:
- 1.5m² at 10mm depth
- 1m² at 15mm depth
- 0.6m² at 25mm depth
- 0.5m² at 50mm depth
For a 20m² garage floor at 20mm depth, you need approximately 20 bags (500kg total). Always add 10% for wastage and uneven substrate depth.
Mixing and application
Preparation
The substrate must be clean, sound, and primed. Remove oil, grease, paint, and loose material. Repair major cracks with epoxy or rapid-set mortar. Prime with a diluted bonding agent (PVA or acrylic primer) per the manufacturer's instructions. Let the primer dry to tacky.
Mixing
Use a forced-action mixer or heavy-duty paddle mixer. Add powder to clean water (typical ratio 4-5 litres per 25kg bag, check the datasheet). Mix for 3-5 minutes until lump-free and flowable. The mix should flow easily but not be watery. Working time is 20-40 minutes depending on temperature.
Pouring and spreading
Pour the mixed concrete onto the primed surface, starting at the furthest point. It will flow, but use a rake or plasterer's trowel to encourage it into corners. For depths over 20mm, use a spiked roller to release trapped air. Work quickly because setting begins within 30 minutes.
Curing
Protect from rapid drying, direct sunlight, and rain. Cover with polythene if outdoors. Foot traffic after 4-6 hours (check datasheet). Light loads after 24 hours. Full cure and maximum strength after 7-28 days depending on temperature and depth.
Exterior-grade vs interior products
Interior self leveling concrete
Standard products designed for dry, protected environments. Not resistant to freeze-thaw cycling or prolonged wet conditions. Use for garages, workshops, basements, and commercial interiors.
Exterior-grade self leveling concrete
Enhanced with additives to resist water penetration, freeze-thaw damage, and UV degradation. More expensive (£15-18 per bag vs £10-12). Essential for outdoor use in the UK climate. Check the product datasheet for frost resistance rating (usually to -15°C or better).
Fibre-reinforced options
Some products include polypropylene or glass fibres to improve crack resistance. Useful for large areas (over 20m²) or areas with slight movement. Adds £2-4 per bag to the cost.
Strength and load-bearing capacity
Self leveling concrete achieves compressive strength of 30-50 MPa (megapascals) after 28 days. This is suitable for:
- Pedestrian traffic: Foot traffic, trolleys, wheelchairs.
- Light vehicular: Cars, vans, forklifts (at 25mm+ depth).
- Racking and static loads: Warehouse racking, machinery, storage.
For heavy-duty applications (HGVs, constant forklift traffic), use 50mm depth or traditional structural concrete. Consult a structural engineer for loads over 5 tonnes/m².
Cost and budget
Material costs for self leveling concrete:
- Standard interior grade: £10-12 per 25kg bag
- Exterior grade: £15-18 per 25kg bag
- Fibre-reinforced: £14-20 per 25kg bag
- Primer: £15-25 per 5L (covers 20-30m²)
Example project: 20m² garage floor at 20mm depth
- Self leveling concrete: 20 bags x £12 = £240
- Primer: 1 x 5L = £20
- Total material cost: £260
Labour (if hiring a contractor): £200-400 for a 20m² area depending on access, complexity, and region. Total installed cost: £450-650.
Finishing options
Self leveling concrete cures to a smooth but slightly textured surface. Finish options:
- Epoxy or resin coating: Seals the surface, easy to clean, chemical-resistant. Common in garages and workshops. Costs £5-12/m² for materials.
- Floor paint: Cheaper than epoxy (£2-4/m²) but less durable. Use garage floor paint for best results.
- Tiles: Suitable substrate for ceramic or porcelain tiles. Prime before tiling.
- Polished finish: Grind and polish with diamond pads for a smooth, shiny surface. Industrial look. Requires specialist equipment.
Related guides
Sources
- Sika UK, "Sikagard Self Leveling Concrete Technical Datasheet" (2025)
- British Standard BS 8204-2:2022, "Screeds, bases and in-situ floorings. Concrete wearing surfaces"
- Ronacrete, "Flexcrete SLC Product Guide and Application Manual" (2024)
- The Concrete Society, "Technical Report 34: Concrete industrial ground floors" (4th edition, 2023)
- Larsen Building Products, "Fast Floor Self Leveling Concrete Specification" (2025)