Concrete overlay
A cementitious layer applied over existing concrete to restore a worn surface or provide a new decorative finish, ranging from thin skim coats to structural toppings.
What does concrete overlay mean?
Overlay success is almost entirely a bond question, which means the existing surface must be sound, clean, profiled, and free of sealers, curing compounds, and laitance. Overlays cannot fix a structurally failing slab; cracks in the substrate telegraph through unless specifically detailed. Polymer-modified products dominate the thin decorative market because they bond and flex better than plain cement mixes.
In practice
Resurfacing a spalled patio is realistic if the slab is stable, and a waste of money if the slab is still moving.