Cosmetic internal wall cracks are typically thin, stable, and limited to the plaster, paint, or plasterboard joints. These are commonly caused by normal settling, seasonal movement, temperature changes, or minor shrinkage in building materials over time.
Hairline cracks that do not continue to widen and are not accompanied by movement are usually not considered structural concerns. Cosmetic cracking can often be repaired by scraping away any loose material, patching the crack with a suitable filler or joint compound, sanding smooth, and repainting.
Structural cracks, however, tend to be wider, continue to grow over time, or appear alongside other warning signs such as doors or windows sticking, uneven floors, bowing walls, sagging ceilings, or gaps reopening after repairs.
In older double brick homes, it is common for structural cracking to transfer from the external brickwork through to the internal walls. Cracks wider than a few millimetres, diagonal cracking around doors and windows, or recurring movement can indicate movement within the building structure or foundation.
If you are unsure, monitor the cracks over several weeks or months to see whether they change in size or shape. You can also mark the ends of the crack with pencil and date them to track movement.
If there is noticeable progression or any signs of structural movement, it would be advisable to have the area assessed by a qualified builder or structural engineer before carrying out cosmetic repairs. – MitchellMc
Unfortunately, it is often impossible to know the extent of repairs required without removing the render or plaster to inspect what lies beneath. Cracks can indicate movement of some kind, but it is difficult to determine how significant that movement is from the surface alone.
Hairline cracks that are thin, stable, and limited to the surface coating are usually cosmetic and commonly caused by normal settlement or minor movement around doors and windows. These can often be repaired by V-grooving the crack, applying mesh tape if required, and patching or re-rendering the area.
More significant cracks may require the render or plaster to be removed so the underlying structure can be inspected. If the masonry beneath appears sound with no stepped cracking through the mortar joints, repairs may only involve repointing and re-rendering.
However, if there are signs of structural movement, the underlying issue should be addressed before cosmetic repairs are carried out. If unsure, it is best to have the area assessed by a qualified builder or structural engineer. – JacobZ
