This is part three of a multipart series “A Guide to Wall Plastering“:
Contents: “Types of Plasters and Tools and Materials required for plastering a wall” is an overview of the series.
Part 1: “A Step-By-Step Guide To Mixing Plaster”, this step-by-step guide to Mixing plaster will help you understand the basics of mixing Plaster.
Part 2: “A Step-By-Step Guide to Plastering your wall”, this step-by-step guide to plastering will ease you through the job. Hopefully, the finished result will look as if a professional completed it.
Part 3: “Reasons for the cracks in plaster”, In this part, you will learn about the reasons for the cracks in plaster. (This Article)
Part 4: “A Step-By-Step Guide to Repair Cracks in Plaster Walls”, this step-by-step guide to Repair Cracks in Plaster Walls will help you understand how to fix the cracks in the plaster wall quickly.
This post will be updated as new sections are released.…
Types of Cracks in Plaster:
- Hairline Cracks
- Non-structural cracks
- Structural cracks
- Lack of hardness
Size of the cracks
- Hairline cracks:- less than 0.1 mm
- Fine cracks:- Cracks up to 1mm in width
- Easy Filled Cracks:- Cracks up to 5mm in width
- Windows and door frame damage:- Cracks up to 15 to 25 mm
- Structural damage:- The widths of the cracks is greater than 25 mm
Some reasons for cracks in Plaster are:
- Non-structural cracks as a result of over trowelling a rich mix.
- Cracks in Plaster due to the Effect of the Seasonal Change
- Structural cracks caused by differential movement of the foundations, moisture expansion or drying shrinkage of masonry units, or thermal movement of the roof.
- Crack in the plaster because of the Debonding
- Crack in the plaster because of the Shrinkage
- Cracks in Plaster due to Poor Construction Practice
- Crack in the plaster because of the hardness or strength of plaster.
- Cracks in Plaster due to the Chemical Reaction
- Cracks in Wall/Structural Elements
- Crack in the plaster because of the thickness.
- Damage due to damp.
- Crushed or decayed internal structural timber.
- Tree root growth.
- Unstable adjacent walls.
- Lack of foundation.
- Fractured masonry.
- Lowering of groundwater.
- Road traffic vibration.
1) Plastic shrinkage cracking
The cracking that is present when an excessive amount of water is lost from the Plaster in the first hours after the application is known as plastic shrinkage cracking.
2) Dry shrinkage cracks
Dry shrinkage cracks are due to moisture loss after the plaster has hardened and the plaster will always shrink and Crack. It is always due to very high cement content and those cement mortar which are made of poor quality of sand having high water requirement and this type of cracks are normally stable and can be filled with property filler and painted over.
3) Structural cracks
Structural cracks are visible in plaster resulting from cracking of walls are known as structural cracks. This can be caused by differential movement of the foundation, moisture expansion, drying shrinkage of the brick wall and thermal movement of the roof slab and this type of cracks often forms in a straight vertical line or horizontal line or in steeped diagonal lines.
Debonding of plaster is often noticed as a hollow sound when the surface is tapped. In this process, plaster is debonded from the wall. Because the outside layer of plaster that is exposed to the air will shrink at a different rate from the Plaster which is in contact with the wall. It is mainly caused due to the thick layer of plaster
5) Lack of hardness
Using poor quality of cement mortar will have lack of hardness that has an insufficient amount of cement and uses more amount of sand containing dust and by mixing poor quality of water and addition of extra water after first mixing and Rapid drying in full Sun causes lack of hardness and cracks in plastering work.
Greening is the term given to the appearance of plaster walls when the position of mortar joints are clearly visible through the Plaster. It is mainly caused due to the difference in suction capacity between the brick walls and the cement mortar
Expansion is noticeable and this includes swelling, softening, layer cracking and spalling of the Plaster.
It is mainly caused due to gypsum-based products in the mix. Under moist conditions, the sulphate from the gypsum reacts with the Portland cement paste and forms compounds of increased volume which disrupt the Plaster.
The conical fragments that break out of the surface of plaster leaving the holes which vary in size are termed as popping. It is mainly caused by the presence of contaminant particles in the mix which react with the moisture in the mix and cause cavities in the Plaster.
Contaminant particles usually you can see are seeds and other organic materials particles of dead burnt lime and the cause of popping has been removed the hole can be filled with filler and painted cover