Published
Faced with an industrial floor that dusts and is covered in fine crazing, the first thought is usually that the concrete class was too low. Usually it was not. The problem is what happened at the surface on the first day after pouring.
Why curing is needed
Concrete gains strength from the reaction between cement and water — hydration. That reaction takes days and needs water. If surface water evaporates early, hydration near the surface is left unfinished.
The result is visible: the surface is weaker than the section beneath it, it dusts as soon as traffic starts, and plastic shrinkage cracks appear. That weak layer cannot be strengthened afterwards — only ground off.
A curing compound forms a thin film that slows evaporation and lets hydration complete.
The three most common mistakes
First, timing: the compound must go on as soon as the bleed water has gone. Applied too early it mixes into the water and no film forms; too late and the water it was meant to protect has already left.
Second, coverage: the film has to be continuous. A gap in a thin layer you cannot inspect by eye means uncured concrete in that area.
Third, compatibility: if a coating, epoxy or surface hardener is to follow, the curing compound has to be compatible with it. Otherwise the next layer will not bond and removing the cure film becomes a work item of its own.
Its relationship with hardeners
Sodium- and lithium-based surface hardeners bind the free lime at the surface and raise abrasion resistance. They do not replace curing, though; they work in addition to it.
The order matters: applying a hardener to a weak, uncured surface achieves little beyond hardening the weak layer.