Self-levelling screed
Self-levelling screed is a fluid cement or gypsum topping that flows to level, used to correct slab tolerances before tile, timber, or vinyl flooring.
Ask Chalkline about this →A self-levelling screed (also called a self-levelling compound or SLC) is a fluid cement-polymer or gypsum-based topping that flows out under its own weight to a horizontal level, used to correct out-of-tolerance slabs before tile, timber, or vinyl flooring goes down. It differs from a traditional hand-laid screed in two ways: it is poured rather than trowelled, and it self-finishes to level instead of needing the tradesman to set the level.
When to use it
Self-levelling screeds suit situations where a hand-laid screed is either slower or impractical:
- Correcting slab tolerances: a slab finished outside the deflection or flatness tolerance the flooring system needs.
- Bringing multiple slab pours to one level (different rooms cast at slightly different heights).
- Setting falls on small or complex shapes where a hand-trowelled screed is fiddly.
- Embedding underfloor heating: many SLCs are designed to pour over heating pipes or cables.
For larger area corrections, structural toppings, or wet-area falls under tile, a hand-laid bedding screed by the tiler is often still the right call. SLCs sit alongside hand screed, not as a universal replacement.
How it goes down
- Substrate prep is critical. The substrate has to be clean, sound, and primed per the SLC manufacturer’s spec; bond failure is the leading defect with self-levellers.
- Application thickness: most SLC products work in the 3 to 50 mm range, depending on the product and whether reinforcement (mesh, dimpled mat) is required at the thicker end. Outside that band, the manufacturer’s spec dictates.
- Mix and pour: powder + water (or proprietary mix) in a forced-action mixer, poured and spread with a smoothing rake; the product does the levelling.
- Cure time: walkable in hours, ready for flooring in 1 to 3 days depending on product and thickness.
Common Australian products include Ardex K15, Mapei Ultraplan, and Sika Level ranges. Each has its own primer and thickness rules; specify by product name to avoid substitution surprises.
Why it matters
The flooring you fix to an uncorrected out-of-tolerance slab inherits the slab’s tolerance. Lippage in large-format tile, hollow-feel in vinyl plank, and bouncy timber floors over high spots all trace back to the substrate. A self-levelling screed at substrate stage is far cheaper than rectifying the finished floor.
Also known as: self-levelling compound, SLC, flowing screed, self-levelling underlayment.
Category: Materials / floor toppings
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Last updated: 2026-05-29. Verified: 2026-05-29. Quarterly review for currency.