Fibre dosage is specified per m³ of concrete, and it varies significantly depending on the fibre type and what it needs to achieve. This guide gives typical dosage ranges by fibre category, and explains why the exact figure always comes from the manufacturer's data sheet or a structural engineer, not a single universal number.
For the mixing process itself, see our guide on how to add fibres to concrete.
Polypropylene Micro-Fibre: Shrinkage Crack Control
Standard polypropylene micro-fibres, used for plastic-shrinkage crack control on driveways, patios, and domestic slabs, are typically dosed around 0.9kg per m³, commonly supplied in a single pre-measured bag sized for a standard mixer or truck load. This is a low dosage relative to the other categories, since micro-fibres are working against early-age shrinkage rather than carrying structural load.
Structural Macro-Synthetic Fibre
Macro-synthetic fibres, a coarser polypropylene product engineered for load-bearing performance, are dosed significantly higher than micro-fibres, typically in the range of several kilograms per m³ depending on the product and the structural requirement being replaced. This dosage is application-specific and comes from the manufacturer's engineered data for the required performance, not a fixed rule of thumb.
Steel Fibre
Steel fibres for structural applications, replacing mesh or contributing to load-bearing capacity in industrial floors, are typically dosed at the highest rates of the three categories, often in the tens of kilograms per m³. As with macro-synthetic fibre, the exact dosage is engineered for the specific slab, loading, and mesh specification it is replacing. See our reinforcement types guide for how commercial floor loading determines the specification.
Why There Is No Single Right Answer
Fibre dosage is not a single figure you can apply universally. It depends on the fibre product (different manufacturers' fibres perform differently at the same dose), the application (crack control versus structural load-bearing), and, for structural applications, the specific loading a structural engineer has calculated. Always follow the manufacturer's data sheet for the specific product, or an engineer's specification for structural applications, rather than a generic dosage figure from a different product or project.
Frequently Asked Questions
Is fibre dosage the same for every application?
No. Dosage depends on the fibre product, the fibre type (micro-synthetic, macro-synthetic, or steel), and the performance the application requires. Manufacturer data sheets specify dosage per m³ for their specific product, and structural applications need an engineered dosage, not a generic figure.
What happens if you use too little fibre?
Under-dosing reduces crack control effectiveness for shrinkage applications, and can mean a structural fibre specification fails to provide the load-bearing capacity it was designed to replace, such as steel mesh. Follow the manufacturer's or engineer's specified dosage rather than reducing it to save cost.
What happens if you use too much fibre?
Over-dosing increases the risk of fibre balling during mixing, can reduce workability significantly, and adds unnecessary cost without a proportional performance benefit past the specified rate. More fibre is not automatically better reinforcement.
Can Procon 24/7 confirm the right dosage for my project?
Yes. Our fibre-reinforced concrete service doses fibre correctly for your specified application when you order, removing the guesswork of calculating and adding dosage yourself on-site.
Order Fibre-Reinforced Concrete, Correctly Dosed
Skip the dosage calculation entirely. Procon 24/7 supplies fibre-reinforced concrete dosed correctly on-site for your application, across Yorkshire and the North West.
