Screed Requirements for Resilient Flooring: Why Sand–Cement Isn’t Enough

Resilient floor coverings – such as vinyl sheets, vinyl planks and similar products – are far less forgiving of substrate imperfections than ceramic or porcelain tiles. Small defects or weaknesses in the screed can telegraph through as visible indentations and tracks in the finished floor.

ARDEX Technical Services Advisor Chris Brady explains why traditional sand–cement screeds are generally unsuitable beneath resilient flooring, and why engineered screeds are now the standard recommended solution.

Why traditional sand–cement screeds fall short

Site-mixed sand–cement screeds can vary significantly in quality from batch to batch. Common issues include:

– Inconsistent sand-to-cement ratios (too rich or too lean)
– Poor compaction during placement
– Variations in water content and curing conditions

These factors combine to produce screeds with variable and often inadequate compressive strength. While tiles can bridge over many minor flaws without visible issues, resilient floor coverings are a different story.

Because resilient finishes are thin and flexible, they transfer concentrated loads more directly into the substrate. Any weakness or softness in the screed is more likely to show up as:

– Localised indentations
– Wheel tracks from trolleys or hospital beds
– Surface damage under heavy point loads

In heavily trafficked commercial environments such as hospitals, aged care facilities and schools, these defects not only look poor but can eventually compromise hygiene and cleanability.

What the standards say

Australian Standard AS 1884 (Floor coverings – Resilient sheet and tiles – Installation practices) addresses these issues directly. It no longer accepts traditional sand–cement screeds as suitable substrates beneath resilient flooring systems.

Instead, the standard points to engineered screeds – systems with proven, controlled strength and performance characteristics – as the appropriate way to build up falls and levels before resilient finishes are installed.

Engineered screeds: the preferred solution

Engineered screeds are specially designed mortars that:
– Are pre‑bagged and factory-proportioned
– Use carefully graded aggregates and cements
– Incorporate additives to enhance workability, strength and durability

Because all components are measured and blended under controlled conditions, engineered screeds deliver predictable performance every time, removing the variability inherent in hand-mixed sand–cement.

ARDEX offers solutions such as ARDEX A 38 and ARDEX A 48, which are designed to provide high compressive strength and fast-setting characteristics suitable for modern resilient flooring systems (always refer to the latest product datasheets for specific details).

Why strength and indentation resistance matter

Consider a typical healthcare setting: a patient on a bed or trolley can easily weigh well over 200 kg combined. The wheels that carry this load are relatively small, creating a very high point load as they roll across the floor.

With a tile finish, that load is spread across the footprint of the rigid tile, and the tile itself absorbs much of the stress. With resilient flooring, however, the flexible surface conforms to the wheel and transmits the load much more directly into the screed below.

If the screed lacks sufficient strength, those repeated point loads can:

– Crush or deform the screed locally
– Create visible wheel tracks or shallow “valleys” over time
– Lead to premature failure of the floor finish

Engineered screeds are specifically developed to resist these effects, maintaining a stable, even surface under demanding service conditions.

Screeds over membranes: bonded vs floating

One important detail when using engineered screeds is how they interact with waterproofing membranes. Fast-setting engineered screeds can generate significant internal stresses as they cure. If they are bonded directly to a soft or flexible membrane, two things can happen:

– The screed may pull away and de-bond, or
– It may grab strongly enough to distort or damage the membrane itself

For this reason, when engineered screeds are used over membranes, they are typically installed as unbonded or floating screeds, separated from the membrane by a suitable slip layer. This allows the screed to cure and move slightly without imposing damaging stresses on the waterproofing.

Key takeaways for resilient flooring projects

When planning a resilient flooring installation:

– Avoid traditional sand–cement screeds beneath resilient finishes.
– Specify engineered screeds that meet the requirements of AS 1884.
– Pay close attention to substrate strength and indentation resistance, especially in high-load environments like hospitals and commercial buildings.
– Detail engineered screeds as floating systems when installed over membranes.
– Always follow the manufacturer’s recommendations for curing times before applying primers, levelling compounds and resilient floor coverings.

Getting the screed right at the start avoids costly failures and disruptions later. If you’re unsure whether an existing or proposed substrate is suitable for resilient flooring, contact ARDEX Technical Services for project-specific guidance.

ARDEX Technical Hotline: 1800 224 070

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