The substrate is the material carrying the coating: plaster, plasterboard, timber, masonry or something else. Its condition matters as much as its name. A new bare surface, a factory-primed panel and an unknown old painted wall need different decisions.

Before disturbance, establish the coating and material history. Unknown old paint or textured material may need competent assessment for lead or asbestos. A smooth surface or a negative casual test does not clear every underlying layer.

For a first project, choose a small, known modern surface within easy reach, with permission and a compatible system. If its material, dryness or safety remains uncertain, postpone the work and resolve that uncertainty before disturbing it.