Flatness spec
SR1 Flatness on a Poured Screed — What It Means
SR1 is the tightest flatness tolerance in BS 8204. Liquid screed delivers it as standard.
SR (Surface Regularity) is measured with a 2m straight edge. SR1 is ±3mm; SR2 is ±5mm; SR3 is ±10mm. In practice we pour to ±2mm and log it.
Large-format tile, welded vinyl, and thin resin coatings all require SR1. Sand-and-cement rarely gets there. Liquid screed does.
Flatness by finish type
| Finish | Minimum flatness |
|---|---|
| Carpet | SR2 |
| LVT | SR1 or SR2 |
| Ceramic tile under 600mm | SR2 |
| Large-format porcelain (600×1200+) | SR1 |
| Welded vinyl | SR1 |
| Thin resin coating | SR1 |