Facade Cracks: Types and Repair Approaches

How to read facade cracks by shape and location, tell active cracks from stable ones, and choose between cosmetic repair and structural work.

Not every crack on a facade is equally serious. Some are merely cosmetic defects left as the render dried; others are signals that the foundations are settling or the structure is moving. Misreading a crack leads either to expensive unnecessary work or to a serious problem being hidden under paint. So before any repair, look closely at the crack and work out what it is telling you.

Types of crack and what they may mean

The shape, direction and position of a crack say a lot about its cause:

• Fine map cracking (crazing). Thin lines resembling a spider’s web usually come from render or paint shrinking as it dries. Causes include coats that are too thick, rapid drying, working in hot or windy weather and not evening out substrate absorption with primer.
• Straight cracks along a joint line. These appear where different materials meet, such as a concrete frame and block infill. The materials react differently to temperature and moisture, and without reinforcing mesh the render splits along that line.
• Diagonal cracks from window and door corners. Stress concentrates at the corners of openings. A small crack may simply mean mesh was not laid diagonally at the corners, but a wide, growing crack can indicate deformation of the lintel or wall.
• Stepped cracks along mortar joints. In brick and block walls, a crack stepping along the joints is often a sign of uneven foundation settlement.
• Horizontal cracks. These may appear at floor level or below a parapet; causes include thermal movement, expansion of a roof slab or corrosion of embedded metal.

Telling active cracks from stable ones

Before choosing a repair, the key question is whether the crack is still moving. A stable crack formed once and stopped; an active crack widens, lengthens or opens and closes with the seasons.

There are simple ways to check. Mark the ends of the crack in pencil with the date, and measure and record its width. Fix a small plaster or glass tell-tale across the crack; if it breaks, movement is continuing. Monitor for several months, ideally long enough to cover both warm and cold seasons. Note other signs too, such as doors and windows starting to stick or new slopes in floors.

Repairing cosmetic cracks

For crazing and thin, stable cracks, the aim is to stop water getting in and restore the surface. The usual sequence is: clean the surface, remove weak render and flaking paint, prime, apply a thin reinforced coat or a flexible filler, then finish with facade paint. Elastic crack-bridging facade coatings, which stay closed under small movements, work well here.

Simply packing a crack with rigid cement mortar often fails: the mortar shrinks as it dries, and the crack reopens along its edge. Painting over with ordinary paint only hides it for a season.

Joint-line and corner cracks

For cracks at junctions between materials, the render is cut back to a certain width either side, reinforcing mesh is embedded across the line and the render is reapplied. Where movement is unavoidable, it is better to create a controlled joint — a decorative groove filled with flexible sealant — than to try to hide the crack. For small cracks at window corners, diagonal mesh strips are added at the corners.

Structural cracks: cause first, then repair

Stepped, wide or widening cracks, or ones visible on both faces of a wall, should be assessed by a specialist. Here facade repair is the final step. First the cause is investigated: water collecting around the foundations, soil wetting and drying, tree roots, nearby excavation, extra load on the structure. Closing the crack without removing the cause is pointless, because it will open again.

Once the cause is established, strengthening methods are applied according to a design: inserting special reinforcement into mortar joints, injecting the crack, replacing a lintel or underpinning the foundation. Which one is chosen depends on the type of structure and the nature of the movement.

Quick checklist

• Have the crack’s shape and location been recorded and photographed?
• Has it been monitored for movement over several months?
• Is the crack also visible on the inside of the wall?
• Is water collecting around the foundations, or has the ground changed?
• Does the chosen repair method match the cause of the crack?

Zaferoğlu İnşaat carries out the full range of interior and exterior renovation work for apartments, offices and private houses. Mark the crack ends with a date and photograph them monthly; a few months of records tell our specialists much more than a single visit.