If a screed layer isn’t level, it can lead to several problems once the final flooring is installed. Screed, whether sand and cement or liquid screed, is applied over a concrete slab to create a flat base for floor finishes. In the UK, floor flatness is measured using Surface Regularity (SR) with a 2-metre straightedge:
- SR1: maximum 3mm deviation
- SR2: maximum 5mm deviation
- SR3: maximum 10mm deviation
Modern liquid screeds often achieve SR2 or better, while traditional hand-laid screeds may fall closer to SR3 if not installed carefully. If a screed exceeds the required tolerance, it is considered an SR failure.
Why flatness matters
Uneven screed can cause several issues.
Damage to flooring materials
Tiles may crack, adhesives may fail, and vinyl flooring can crease. Timber or laminate floors may lift, squeak, or develop gaps.
Uneven wear
High spots take greater pressure and wear more quickly, while low areas may collect dirt or moisture.
Safety concerns
Raised edges or dips can become trip hazards, especially in busy areas or near door thresholds.
Reduced underfloor heating performance
Uneven screed depth can lead to inconsistent heat transfer and cold spots.
Compliance and warranty issues
Many flooring manufacturers require SR2 tolerance. If this isn’t achieved, it may result in failed inspections or void warranties.
Common causes
Poor preparation, dust or debris on the base, incorrect water ratios, staged pours that create ridges, lack of spiked rolling, and poor site conditions such as draughts or strong sunlight can all lead to uneven screed.
Fixing an uneven screed
Minor issues may be corrected by grinding high spots or applying a thin levelling layer. Larger deviations may require removal and replacement of the screed.
Why choose Floor Screeding London?
With over 15 years of experience, Floor Screeding London installs screed floors across London to tight tolerances, ensuring smooth and reliable results.