Plaster cracking generally occurs for two reasons: movement within the substrate or improper application technique. Identifying the type of crack helps determine whether it is purely cosmetic or indicates a substrate issue.
Cracks from Substrate or Structural Movement
These are the most common type of cracks found in plaster finishes. They usually appear after the plaster has cured, as a result of normal building movement or settling.
How to recognize them:
Fine, hairline cracks that often run in straight lines
Common near doors, windows, corners, and structural junctions
May follow framing or areas of concentrated stress
Why they happen: All buildings experience slight expansion, contraction, and settling over time. Lime plaster, being rigid and mineral-based, may reflect this movement as fine surface cracks.
What they mean:
Typically cosmetic only — not a sign of failure
Cracks may reappear after repair if movement continues
They do not generally affect the durability or breathability of the finish
Cracks from Improper Plaster Application
These cracks form as the plaster dries and result from errors during the application process.
How to recognize them:
Short, Y-shaped or irregular patterns
Appear soon after the surface begins to dry
Commonly occur when plaster is applied too thickly or dries unevenly
Why they happen: If plaster is applied beyond the recommended thickness or dries too quickly, internal stress develops as moisture leaves the material. This causes surface tension cracks known as shrinkage cracks.
What they mean:
Can affect surface appearance and, in severe cases, lead to delamination of the plaster coat
A signal that application conditions may not have been optimal
When to Take a Closer Look
Minor surface cracking is normal in lime plasters where there is structural movement.
Cracks wider than 1/16 inch (1.5 mm) may suggest excessive substrate movement and should be evaluated before refinishing.
Cracking does not typically affect the plaster's performance when the substrate remains stable.
Questions?
Email [email protected] or text 1-800-917-2414 — our team is happy to help.