Does the substrate need to be prepared and smoothed?

For optimal bonding of Slate-Lite, the substrate should be smooth, clean, dust-free and dry.

With "stable" no special preparation is necessary.
Crumbling substrates such as old, crumbling plaster or wallpaper that is already peeling must be primed in advance to ensure a permanent bond between the adhesive and the wall, or a new stable substrate must be created.

Severe unevenness must also be levelled with primer, filled or sanded down.