Floor screeding is the process of applying a blended mixture of cement and graded sand (or a specialized liquid compound) to a structural concrete subfloor. For...
Whether you are extending your home or levelling a bumpy garage floor, the quality of the screed determines the longevity of your final flooring. A poor job can lead to cracking, damp issues, or "hollow" spots that cause expensive floor tiles to snap under pressure.
What Does the Work Involve?
- Subfloor Preparation: Removing debris, dust, and grease from the base concrete to ensure a strong bond.
- Moisture Management: Testing the base for dampness and installing a Damp Proof Membrane (DPM) if required.
- Edge Expansion: Fitting perimeter expansion strips to allow the screed to expand and contract without cracking.
- Priming: Applying a bonding agent or primer to prevent the base from sucking moisture out of the new screed too quickly.
- Mixing and Application: Combining the screed (traditional or flow) and spreading it to the specified depth.
- Levelling: Using a straight edge or dapple bar to achieve a flat, "SR1" (Surface Regularity) grade finish.
- Curing: Protecting the floor from draughts and direct heat while it gains initial strength.
Typical Costs
| Item | Low £ | High £ | Notes |
|---|---|---|---|
| Sand & Cement (per m²) | £18 | £30 | Traditional semi-dry mix; labour and materials included. |
| Liquid / Flow Screed (per m²) | £22 | £40 | Anhydrite or cement-based; ideal for underfloor heating. |
| Minimum Call-out Charge | £500 | £850 | Required for small areas to cover pump hire and setup. |
| Latex Levelling Compound | £15 | £25 | Per m² for thin-set smoothing (3mm - 10mm). |
| DPM & Primer Prep | £6 | £12 | Per m² for moisture barriers and bonding agents. |
Prices vary significantly based on the depth of the screed and the total area. Liquid screeds often have a higher material cost but lower labour time, whereas traditional sand and cement is cheaper in materials but physically demanding and slower to install.
How Long Does It Take?
- Small Room (e.g., Utility or Kitchen): 4 to 6 hours for installation, depending on access.
- Average Ground Floor (50m²): 1 full day for preparation and pouring.
- Foot Traffic: Most screeds can be walked on (carefully) after 24 to 48 hours.
- Full Drying Time: Traditionally 1 day per 1mm of thickness (e.g., 50mm = 50 days) before laying sensitive floors like wood.
DIY or Professional?
While DIY screeding is possible for small patches or sheds, large-scale internal floors are best left to professionals. Achieving a perfectly level finish across a large room is technically difficult; a 5mm error can result in "lippage" on your tiles or bouncy floorboards.
Professional screeders use laser levels and specialized pumping equipment to ensure consistency. Furthermore, if you are installing underfloor heating, a professional ensures the screed is compacted around the pipes to eliminate air pockets, which is vital for heat transfer.
Choosing the Right Tradesperson
- Check Credentials: Look for NVQ Level 2 in Floor Screeding or CSCS cards for site-based workers.
- Equipment: Ask if they use a laser level for accuracy and if they provide their own mixing/pumping plant.
- Insurance: Ensure they have Public Liability insurance (minimum £1m-£2m).
- References: Ask for photos of "dappled" finishes or references from local builders.
Top Tip: Always ask your tradesperson if they will perform a moisture test (hygrometer test) before you lay your final floor covering. This is the only way to be sure the screed is dry enough for wood or LVT.
UK Regulations
- British Standard BS 8204: This code of practice dictates the standards for levelling and surface regularity.
- Part L (Building Regs): If you are screeding over a new floor, you must meet specific insulation (U-value) requirements beneath the screed.
- Testing: For commercial or high-spec residential builds, a "drop hammer" test may be required to check the screed's crushing resistance.
Common Problems
- Cracking/Shrinkage: Often caused by the screed drying too quickly or a lack of expansion joints.
- Laitance: A weak, dusty layer on top of liquid screeds that must be sanded off before tiling.
- Hollow Spots: Occurs when the screed fails to bond to the base concrete, usually due to poor priming.
- Slow Drying: If the room is not properly ventilated or is too cold, the screed may take months to dry, delaying your project.
Frequently Asked Questions
Can I put screed over an existing concrete floor?
Yes, but the thickness matters. If you only need a thin layer (under 10mm), a self-levelling compound is better. For traditional screeds, you usually need at least 35mm-40mm for a bonded finish.
Which is better: Liquid screed or Sand and Cement?
Liquid (flow) screed is superior for underfloor heating as it flows around pipes perfectly. Sand and cement is more cost-effective for smaller areas or floors with a fall (like a wet room).
Do I need a damp proof membrane (DPM)?
If your base concrete is old or shows signs of moisture, a DPM is essential. It prevents ground damp from rising through the screed and ruining your floor finishes.
How soon can I turn on my underfloor heating?
You must wait at least 21 days for cement-based screeds and 7 days for some liquid screeds. The heat must be introduced very gradually (5°C increments) to prevent thermal shock and cracking.
Why is my screed dusty on top?
This is usually "laitance" or a sign that the mix had too much water. It must be mechanically sanded and vacuumed before any adhesive or primer is applied.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
