Why the calendar is not enough
Twenty-eight days is a guideline based on typical conditions. A slab poured in October in a cool, enclosed garage can still read well above coating thresholds at six weeks. An in-situ RH test costs almost nothing and answers the question definitively rather than by assumption.
Curing compounds have to come off
Most new slabs are sprayed with a curing compound to control moisture loss. That film is a bond breaker for any coating, and it does not simply wear away. Diamond grinding removes it as part of normal preparation, which is another reason a new slab still needs a full grind rather than just a clean.
Planning it into a build
On new construction, the practical sequence is to pour early, let the slab cure while other trades work, and coat near the end after drywall and paint but before fixtures and cabinets. Coating too early in a build means protecting a finished floor through months of trade traffic, which rarely goes well.
If you cannot wait
Moisture-tolerant primers exist and can bring a young slab into range earlier, at the cost of an extra product and step. It is a legitimate solution for a construction schedule that cannot move, and it should be a stated line on the quote rather than an assumption.
Want this answered for your slab?
Free site visit with a moisture reading, then a written fixed price. Across the BC Interior.