Identify the type of crack
A fine surface crack, a crack at a material junction and ongoing structural movement are not the same problem. The position, width, pattern and history help determine the appropriate response.
Check the surrounding render
The affected area should be checked for hollow, loose or moisture-damaged material. Patching only the visible line can leave failed material in place around it.
Prepare and reinforce correctly
A suitable repair may involve removing unsound render, cleaning and priming the substrate, rebuilding the base, reinforcing vulnerable areas and matching the existing finish as closely as practical.
Know when further advice is needed
If cracking is active, widespread or connected to building movement, the underlying issue may require assessment by an appropriately qualified building professional before cosmetic repair.
This guide provides general information. The correct system and scope depend on the condition of the individual property.