Floor Screed: Types, Applications & Installation
What is Floor Screed?
Floor screed is a cement-based leveling layer applied over concrete substrates to create:
✔ A perfectly flat surface for final floor coverings
✔ Additional structural strength
✔ Thermal mass for underfloor heating systems
✔ Moisture protection
Typically installed at 25-75mm thickness, screed serves as the critical intermediary between structural concrete and finished flooring.
Types of Floor Screed Explained
1. Traditional Sand-Cement Screed
Composition: 1:3-1:4 cement/sand ratio
Thickness: 50-75mm
Curing Time: 28 days
Best For: Budget projects, industrial floors
Pros:
- Lowest material cost
- High compressive strength (25-30N/mm²)
Cons:
- Long drying times
- Prone to shrinkage cracks
2. Liquid Flowing Screed (Anhydrite)
Composition: Calcium sulfate binder + additives
Thickness: 35-50mm
Curing Time: 7 days (light foot traffic in 24h)
Best For: Underfloor heating, fast-track projects
Pros:
- Self-leveling properties
- Excellent thermal conductivity
- Minimal shrinkage
Cons:
- Requires moisture barrier
- Not suitable for wet areas
3. Polymer-Modified Screed
Composition: Cement + polymer additives
Thickness: 15-40mm
Curing Time: 3-7 days
Best For: Thin applications, heavy traffic areas
Pros:
- High flexural strength
- Bonded to existing substrates
- Crack-resistant
4. Lightweight Foam Screed
Composition: Cement + foam beads
Density: 300-900kg/m³
Best For: Weight-sensitive projects
Key Benefit: 50% lighter than traditional screed
Technical Specifications
| Parameter | Requirements | Test Standard |
|---|---|---|
| Compressive Strength | ≥20N/mm² | EN 13813 |
| Drying Time | 1 day/mm (sand-cement) | BS 8203 |
| Moisture Content | ≤75% RH (for adhesives) | ASTM F2170 |
| Surface Tolerance | ±3mm under 2m straightedge | BS 8204 |
Professional Screed Installation Process
1. Substrate Preparation
- Concrete must reach minimum 20N/mm² strength
- Apply bonding slurry (for bonded screeds)
- Install membrane (for unbonded screeds)
2. Mixing & Application
- Traditional: Mixed on-site, hand-applied
- Liquid: Pump-applied at 15-20m³/hour
- Polymer: Power-mixed for 3-5 minutes
3. Finishing Techniques
- Trowel finish for tile adhesives
- Steel float finish for direct coatings
- Broom finish for exterior applications
4. Critical Curing Process
- First 72 Hours: Prevent rapid drying
- 7-14 Days: Light foot traffic permitted
- 28 Days: Full structural capacity reached
Screed Drying Science
Moisture Testing Methods:
- CM Test (Calcium Carbide) – Instant results
- Hygrometer Testing – BS 8201 compliant
- Polyethylene Sheet Test – 24h assessment
Accelerated Drying Solutions:
- Dehumidification systems
- Underfloor heating activation
- Ventilation optimization
Common Applications
Residential
- Under tile/wood flooring
- Radiant heating systems
- Garage conversions
Commercial
- Retail spaces requiring flatness
- Warehouse mezzanine floors
- Office fit-outs
Industrial
- Food processing facilities
- Manufacturing plants
- Cold storage units
