How To Repair Cracks

Cracks must be repaired immediately when observed otherwise the life of structure will reduce causing structural failure. They not only weaken the building but spoil the beauty of walls also. This write up tells you about repair of cracks in plaster, RCC member, Brick walls, Floor and Fine Cracks.  
The cracks can be prevented at the time of construction. To know more about prevention of cracks during construction, click at the link below.

How to Prevent Cracks in Building

Repair Cracks in Plaster

Two types of cracks are found on surface of plaster i.e. A. Crack with hollow sound in plaster.  B. Crack with no hollow sound in plaster. Hollow sound can be checked by striking the plaster. 

A. Repair cracks giving hollow sound

Remove plaster applying proper cut

Defective plaster should be removed and the edges should be slightly cut in square or rectangular shape to provide a neat joint.

Prepare the surface thoroughly

Clean the surface with wire brushes and wash it. Wet the surface 24 hours before application of cement mortar.

Apply fresh cement mortar and finish the surface

Defective portion should be filled in with cement mortar. Keep the surface wet at least for 3 days. When surface is dry, finish it according to adjoining area on the wall.

B. Repair cracks if it is solid without hollow sound

Clean cracked portion of all loose materials and fill crack seal sealants in cracked portion. Finally finish the surface according to adjoining area. 

Cracks in plastered surface


Cracks in plaster

Prepare surface for Crack Repair


Repair Cracks in plastred Surface

NOTE: Plastering is done after cleaning. To know the process of ‘Plastering’ click on the link
Process of Cement Plastering 

Repair Cracks on RCC Surface

Clean cracked portion and apply guniting

The cracked portion should be widen gently and be cleaned of all loose materials.  Fill the cracked portion by pressure grouting or ‘guniting’. The material for such grouting can be epoxy or cement (with suitable admixture).

Apply epoxy and finish the surface

Epoxy has more strength and adhesion than cement and can go into very thin cracks as fine as 0.1 mm. The surface should be finished according to adjacent area on the wall.
Note: The cracks in RCC members/ structural members should be repaired immediately with consultation form structural engineer/professional.

Repair Cracks on face of plaster

When two components having different elastic properties such as RCC slab and brick work abating each other, the crack on face of plaster is formed between these components due to their thermal expansion. 

Remove plaster and old material

The plaster should be removed from cracked portion. The joints should be widened at least 20 mm to 25 mm in thickness. Clean old material by washing and brushing.

Apply cut and prepare the surface

Apply slight cut on edges in straight line to provide neat joint. Make the surface damp 24 hours before application of new plaster.

Apply cement mortar

Cement mortar should be applied on defective portion. Make 20 mm wide and 25 mm thick groove at the junction of two materials/components.

Do curing and finishing

Keep the surface wet at least for 3 days. When surface is dry, finish it according to adjacent area on wall. 

Cracks in RCC surface

Repair cracks in RCC surface

Repair Cracks in Masonry Walls

Two types of cracks are seen in masonry walls i.e.  A. Crack in mortar joints of walls.  B. Crack in bricks/Diagonal Cracks  

A. Repair cracks in mortar joints of walls

Remove mortar

The mortar should be removed from cracked joint with the help of iron tools at least up to 25 mm depth. All loose material should be cleaned from cracked portion.

Wet the surface and apply cement mortar

Cracked portion must be kept moist at least for 24 hours before doing repair. Fill in the joints with cement mortar of coarse sand in 1:4.

Do curing and finishing

After filling the joints with cement mortar, keep the repaired surface wet at least for 3 days. After drying the surface, finish the repaired area according to the adjoining area.

Crack in Wall


B. Repair cracks in bricks/diagonal cracks 

Remove broken bricks

Before doing any repair of cracks, make sure that the cracks are stabilized and are not widening further. Remove broken bricks by scratching cement mortar from the joints gently.

Prepare the surface

All loose material should be cleaned from the portion by brushing and washing. Wet the surface 24 hours before application of new plaster.

Fix new bricks thoroughly

Lay fresh cement mortar with coarse sand in 1:4 and fix new bricks. Fill all joints around bricks with mortar tightly with the help of iron tools. 

Do curing and finishing

The repaired surface should be kept moist up to 7 days.  When surface is dry, it should be finished according to adjoining area. 


Repair Cracks in Floor  

Remove loose material and apply mortar

Create V shape groove in cracked portion and remove all loose material by washing and brushing. Fill in the groove with polymer modified mortar (for wide cracks) or with polymer modified cement grout (for thin cracks).

Remove cracked panel or material

If there are many cracks in the floor, remove cracked panels and old materials.

Prepare the surface and lay new panel

Clean the panel by washing and brushing. Prepare floor material according to the existing floor and lay new panel.
Note: To know more on ‘How to Lay Floor’ in detail, you can click at the link given below on our website. 

Floor Construction 

Repair Hair Cracks in plaster

Broaden the crack gently

Widen the crack about ¼ inches with chisel and remove all loose plaster from the cracked portion.  

Apply vinyl spackle compound

Use vinyl spackle compound to fill the cracked portion. Press the vinyl spackle into the crack and let it dry. Sand or sponge the surface smooth.

Seal the patch and finish the surface

Seal the patch with proper priming coat and finish it with proper shade according to the adjoining area.

Repair Fine cracks

  • Apply surface water proof coating on the entire area having very fine cracks (especially on roof) where filling /sealing of each individual crack is not possible. 
  • Do proper curing of repaired area at least for 3 days.
Cracks in building are a common occurrence and it is important to understand the causes and the measures to be taken for their prevention.Materials such as bricks,mortar and concrete, which contain considerable quantity of water at the time of construction, dry out subsequently and under go major contraction.
Cracks can happen due to foundation movements and settlements of building, thermal movements, chemical reactions, elastic deformations and shrinkage etc. in buildings. They can damage plaster of walls, ceilings and destroy the beauty of the structure also. Let’s know their reasons in detail and get preventive measures.
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