Thin overlays (under 20mm thick) are vulnerable to cracking, shrinkage, and movement stress — especially on large spans or exterior surfaces. Reinforcing your overlay properly with mesh or fibres dramatically improves strength, flexibility, and long-term durability. In this guide, we’ll explain when reinforcement is necessary and exactly how to install it for reliable, professional results.
Reinforcement is recommended if your overlay is thinner than 20mm, installed over cracked or moving substrates, exposed to temperature swings, subject to mechanical traffic, or installed outdoors. Very stable, indoor overlays may sometimes omit reinforcement, but for critical surfaces, it’s a must. Always check overlay product datasheets — many manufacturers require mesh or fibre use above certain span or thickness limits.
For very thin polymer overlays (5–15mm), alkali-resistant (AR) fibreglass mesh is often ideal. For thicker overlays or heavier-duty work (10–30mm), galvanized welded steel mesh is better. Fibres (polypropylene, glass, or steel) can be mixed directly into some overlay mortars at specific dosages. Mesh provides macro reinforcement against major cracking; fibres help control microcracking across the matrix. Sometimes both are used together for maximum performance.
Surface preparation must be completed before laying mesh or applying fibre-reinforced overlays. Grind, shot blast, vacuum, repair cracks and voids, and prime or apply a slurry bond coat if needed. Reinforcement improves the overlay, but cannot make up for poor substrate prep. A clean, roughened surface is critical to lock everything together mechanically and chemically for full-system strength.
Mesh must sit fully embedded within the overlay thickness — typically ⅓ from the bottom. Lay fibreglass mesh or welded steel mesh onto the primed substrate. Overlap mesh sections by at least 50mm to prevent crack planes forming at seams. Pin or weigh down mesh temporarily if needed. When placing overlay material, carefully work the mortar through and over the mesh to eliminate air pockets and fully surround it. Avoid leaving mesh floating dry above the substrate.
On irregular floors, vertical surfaces, small patches, or thin skim coats, installing mesh may not be practical. In these cases, microfibres or hybrid fibre systems can be mixed into the overlay mortar. Follow manufacturer dosage instructions — typically 0.9–2kg per cubic metre. Properly dispersed fibres help reduce shrinkage cracking, increase toughness, and improve overall matrix cohesion without the hassle of manually installing mesh sheets.
Reinforcement helps — but good curing is still essential. Protect overlays from rapid drying, direct sun, or wind exposure. Use curing membranes, damp coverings, or misting systems where required. Proper curing reduces surface shrinkage stresses that can overwhelm even reinforced overlays. Only after full curing should overlays be subjected to grinding, sealing, or traffic loading according to the product's technical guide.
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