The problem it solves
Cracks in a concrete floor almost never come from the load. They come from the first hours, when the material is still plastic, loses water to evaporation and shrinks. Because it is restrained — bonded to the substrate, the edges, the formwork — that shrinkage cannot accommodate itself freely and resolves by opening fissures.
In Mexicali and Tijuana the phenomenon accelerates. Temperatures above 40 °C, low humidity and dry wind cut the working window to minutes. Once the crack appears it is too late: it can be patched, but the plane of weakness is there and over time it opens again.
What microfibre actually does
Distributed uniformly through the mix, the microfibres work as three-dimensional reinforcement spread across the whole mass. When the plastic concrete starts to shrink, the fibres stitch those microcracks before they become visible cracks. It is control of plastic and drying shrinkage cracking.
The side effect is just as valuable: they reduce bleeding and segregation in the fresh state. Less water migrating to the surface means a more homogeneous top layer, and that translates into tighter, more uniform surfaces with better appearance at finishing.
What it improves and what it does not
It does improve: flexural, impact and abrasion resistance. A floor with microfibre takes forklift traffic, a dropped pallet and the wear of a manoeuvring area better. And of course it reduces and controls shrinkage cracking.
It does not replace: reinforcing steel. Microfibre controls a phenomenon of the first hours; rebar and mesh work for structural strength against service loads. They are two different functions and in most floors they coexist. Anyone selling microfibre as a substitute for reinforcement is selling it wrong.
When to order it
Whenever you pour in hot weather, wind or low humidity. And on any large exposed surface, because that is where plastic shrinkage does the most damage: industrial floors, manufacturing plants, sidewalks, walkways, manoeuvring yards and pavements.
Also on elements where a crack is not merely cosmetic: cisterns, elements that must stay watertight and surfaces that will receive an expensive finish on top. In those cases the extra cost of fibre is less than the cost of repairing a crack later.
What does not change
Placement is the same: it is placed, vibrated and finished the same way. With correct finishing the surface closes and the fibre is not noticeable; loose fibre only shows if the surface is overworked or poorly cured.
And most important: microfibre does not replace curing. It helps, but immediate curing and protection from sun and wind remain mandatory. A poorly cured floor with microfibre cracks just the same, only a little later.
