Floor Levelling Compound & Self-Levelling Screed Calculator
Calculate the number of bags of self-levelling floor compound needed for any room area and depth, including feather-edge repairs.
Floor Levelling Guide
Coverage Rates
Self-levelling compound coverage at 1mm depth: standard SLC (Ardex F6, Mapei Ultraplan): approximately 1.7-1.8 kg/m²/mm. Feather-edge compound: approximately 1.5-1.6 kg/m²/mm. Heavy-duty screed: approximately 1.6 kg/m²/mm. A 25kg bag at 3mm depth: 25/(1.7×3) = approximately 4.9 m². For 20m² at 3mm depth: 20 × 1.7 × 3 = 102 kg = 4.1 bags → buy 5 bags. Add 10% waste: 4.5 bags → buy 5 bags. Always check the manufacturer datasheet — coverage rates vary significantly between products.
Preparation is Critical
Self-levelling compound requires meticulous preparation — failures are almost always caused by poor prep. Steps: remove all dust, grease, and contamination. Repair cracks and holes in the substrate (use floor repair compound, not filler). Vacuum thoroughly. Apply primer: SLC primer is essential for porous substrates (concrete, sand/cement screed, plywood) — prevents the substrate absorbing water from the SLC before it can set properly. Allow primer to dry completely (usually 1-3 hours). Prime lo
Mixing and Pouring
Mix to a fluid, self-smoothing consistency: add powder to water (not water to powder) to minimise lumps. Use a drill with paddle attachment — not a trowel. Mix for 3-4 minutes until completely smooth. Typical water ratio: 5.5-6 litres per 25kg bag. Pour immediately — most SLC has only 20-30 minutes working time. Pour along one wall and allow to flow. Assist flow with a spiked roller or smoother on thicker pours. Do not walk on it until it has set (typically 3-6 hours for foot traffic, 24 hours f
When to Use Levelling Compound
SLC is appropriate for: creating a smooth, level surface for vinyl, LVT, or carpet. Covering old tile adhesive or minor undulations (up to 20mm in most cases). Re-levelling after removing old floor coverings. Feathering out slight humps or hollows. SLC is not appropriate for: structural repairs (use concrete repair mortar). Wet areas without waterproofing membrane (SLC is not waterproof). Areas with rising damp (treat damp first, then level). Depths over 50mm in one pour (apply in layers). If th
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