Adhesive selection is often treated as a trade decision made on site. It is more accurately a specification decision made against three substrate variables: porosity, residual moisture and thermal regime.
Porosity determines open time and coverage rate. A dense, polished slab requires a longer open time and higher adhesive weight than an absorbent, primed screed. Residual moisture determines chemistry — MS-polymer or two-part epoxy systems above 4% CM, dispersion adhesives below.
Thermal regime
Underfloor heating imposes its own constraint. The adhesive must remain elastic through the thermal cycle without hardening at the peak or losing bond at the trough. Manufacturer data sheets state a heating suitability; the specification should reference it directly.