If a screed isn’t level, it can cause everything from cracked tiles to unsafe trip hazards. Screed (sand/cement or liquid) is laid over the slab to create a flat base for the final floor finish. In the UK, flatness is measured as Surface Regularity (SR) using a 2m straightedge:
- SR1: max 3mm deviation
- SR2: max 5mm deviation
- SR3: max 10mm deviation
Many modern liquid/self-levelling screeds typically achieve SR2 or better, while hand-laid sand/cement can often fall closer to SR3 if not installed carefully. If the floor is outside the required SR level, it’s an SR tolerance failure.
Why flatness matters
An uneven screed can:
- Damage floor coverings: adhesives struggle on high/low spots; tiles can lose bond and crack, sheet vinyl can crease, and timber/laminate may squeak, lift, or show gaps.
- Increase wear: high spots take more load and wear faster; low spots trap dirt and moisture.
- Create safety risks: ridges and dips become trip points, especially at thresholds or in busy areas.
- Reduce UFH performance: uneven depth can create cold spots and inefficient heat spread.
- Cause compliance and warranty issues: many floor finishes (especially vinyl) require SR2; failing tolerance can lead to snags, disputes, failed inspections, or voided manufacturer warranties.
Common causes
Poor prep (dust/debris/missing primer), incorrect water ratio, pours that set in stages (ridges/cold joints), lack of spiked rolling (bumps/air), rushing, or poor site conditions (draughts/sun/temperature swings).
Fixing an out-of-tolerance screed
- Minor issues (a few mm): grind high spots or apply a thin self-levelling layer.
- Major deviations: removal and re-screed is often the only reliable fix (sometimes a second pumped layer can help, within limits).
Why LMA
LMA installs to tight tolerances with 15+ years’ experience, aiming for SR2 or better, with clear communication, tidy work, and the confidence that if something isn’t right, we’ll put it right.
Don’t let an unlevel screed ruin your floor. Contact LMA today for expert screeding in London and the South East. We’ll ensure your screed is within tolerance giving you a stable, flat base that protects your investment. Your floors deserve the best foundation, and our team is ready to deliver it.