Fibre-Reinforced Liquid Screed: What the Fibres Do

As screed cures, it loses moisture and shrinks slightly; if this happens unevenly or too quickly, fine cracks can form at the surface. Fibres bridge these micro-cracks as they start to form, limiting their width and spread rather than eliminating shrinkage altogether.

Because fibres are mixed through the entire batch, they're present at every point in the pour without needing site labour to position them — useful in flowing screed installations where the pumped, fluid nature of the material makes laying a mesh sheet impractical.

Steel mesh is designed to resist tensile bending stresses at a specific plane in a slab, which matters for structural or heavily loaded floors. Fibres address a different failure mode — shrinkage cracking and micro-crack propagation — so the two aren't functionally interchangeable even though both are described loosely as 'reinforcement'.

For most residential floating and unbonded liquid screeds, fibre dosing is the manufacturer-recommended approach and mesh isn't typically needed; heavier commercial or structural applications may call for a different specification, which should be confirmed with the screed manufacturer and structural designer.

Polypropylene fibres are the most common choice in domestic and light commercial screeds, chosen for ease of mixing, corrosion resistance and a good contribution to controlling plastic shrinkage without affecting the finish or sanding process for calcium sulphate screeds.

Steel fibres can offer greater contribution to impact and abrasion resistance in heavier-duty applications, but need compatible mix design and finishing methods, and are less commonly specified for standard domestic floors where polypropylene fibre already meets the performance requirement.

Fibre dosing addresses shrinkage-related micro-cracking, but it won't compensate for an under-thickness pour, a poorly prepared substrate, missing movement joints or incorrect drying — these remain the responsibility of correct design and site practice regardless of fibre content.

Where a floor has cracked despite fibre reinforcement, the cause is generally traced to one of these other factors rather than a failure of the fibres themselves, which is why diagnosing cracking properly matters more than simply increasing fibre dosage.