Cement plaster is a widely used material in the construction industry for both aesthetic appeal and structural protection.
However, despite its strength and durability, it is not uncommon for cracks to appear over time, causing frustration for homeowners and builders alike.
But do you know what causes fractures in cement and plaster? Understanding the root causes of these cracks is key to preventing them and ensuring the longevity of your structures.
In this article, we’ll explore the primary causes of cracks in cement plaster, explain why they form, and offer practical tips to avoid or repair them.
Whether you’re a homeowner, builder, or DIY enthusiast, this guide will help you maintain crack-free, visually appealing walls.
Let’s get straight to the point
Cracks in cement plaster, despite its durability, are common due to various factors.
Key causes include water damage, poor construction practices (like improper mix ratios or inadequate curing), temperature fluctuations, corrosion of reinforcement bars, structural movement (from soil shifts or natural disasters), and root growth from nearby vegetation.
Identifying the type of crack (hairline, vertical, or diagonal) helps in determining the repair approach, from simple filler applications to structural reinforcements.
Preventing cracks involves proper surface preparation, correct material use, and addressing foundational issues early in construction.
What Is Cement Plaster?
Before diving into the reasons for cracks, let’s start with understanding what cement plaster is.
Cement plaster, often referred to as cement stucco, is a mixture of cement, sand, and water, applied in layers to smooth walls and protect surfaces.
It is highly versatile and can be used both indoors and outdoors.
Benefits of Cement Plaster
- Durability: It’s strong and resistant to wear and tear.
- Aesthetic Appeal: Offers a smooth, visually pleasing finish.
- Fire Resistance: Cement plaster is naturally fire-resistant.
- Versatility: Can be applied to various surfaces, including brick, concrete, and metal.
- Weather Protection: Acts as a barrier against moisture and environmental damage.
While it offers many advantages, cracks can still develop in cement plaster under certain conditions. Let’s explore the main causes.
Causes of Cracks in Cement Plaster
1. Water Damage
One of the most common causes of cracks in cement plaster is water damage. When water penetrates the plaster, it can weaken the material, causing expansion and contraction. This movement leads to fissures that compromise the structure’s integrity.
Moisture-related cracks are especially prevalent in areas with poor drainage systems or leaky roofing.
In Australia’s fluctuating climate, this is a frequent issue, and it can also attract pests like termites, which further exploit the cracks.
Preventive Measures:
- Ensure proper waterproofing during construction.
- Regularly inspect for water leaks and fix them immediately.
- Install effective drainage systems to divert water away from the walls.
2. Poor Construction Practices
Subpar construction practices are another leading cause of cracks in cement plaster.
Whether due to cost-cutting measures or lack of knowledge, these errors can lead to significant structural issues.
Common Poor Practices:
- Inadequate surface preparation: Not cleaning the surface properly before applying plaster leads to poor adhesion.
- Wrong mix ratios: Incorrect cement-to-sand ratios weaken the plaster.
- Thick layers: Applying excessively thick coats can cause the plaster to crack as it dries and contracts.
- Improper curing: Plaster that is not allowed to cure properly remains weak and prone to cracking.
How to Avoid:
- Always ensure correct mix ratios.
- Prepare the surface by cleaning it and removing any oil or grease stains.
- Allow for adequate curing time between layers of plaster.
3. Temperature Fluctuations
In Australia, extreme temperature changes can have a significant impact on cement plaster.
Rapid temperature fluctuations cause the plaster to expand and contract, which leads to the development of cracks.
Solution:
To mitigate temperature-related cracks:
- Use thermal insulation to protect walls from extreme weather.
- Apply flexible additives in the plaster mix to allow for minor expansions and contractions.
4. Corrosion of Reinforcements
When reinforcement bars within the wall begin to corrode, they can exert pressure on the surrounding plaster, causing cracks.
This occurs when moisture infiltrates the plaster and reacts with the metal, leading to rust formation, which expands and damages the plaster.
Preventive Tip:
Ensure that reinforcement bars are properly embedded within the concrete and adequately protected from moisture infiltration during the construction process.
5. Structural Movements
Foundation movements are another common cause of cracks.
regions with reactive soils, like parts of Australia, foundations can shift due to soil expansion and contraction caused by seasonal changes.
Additionally, natural disasters such as earthquakes or floods can also lead to cracks in cement plaster.
How to Prevent Structural Cracks:
- Conduct a geotechnical analysis before building to understand the soil type and its movement tendencies.
- Reinforce foundations in areas prone to shifting soils.
6. Growth of Vegetation
Trees and other vegetation growing near your home can cause cracks in your plaster. As the roots expand, they can apply pressure on the foundation and walls, leading to cracks.
How to Prevent:
- Avoid planting large trees near the foundation of your home.
- Regularly inspect the foundation area for any signs of root intrusion.
Types of Cracks and How to Identify Them
Understanding the type of crack and its cause is essential to making the right repairs. Here’s how you can identify different types of cracks:
1. Hairline Cracks
These are minor cracks that typically don’t indicate any major structural issues. They usually occur due to shrinkage of the plaster during drying.
Repair:
Fill them with a cement-based filler and repaint the surface.
2. Vertical Cracks
Vertical cracks can indicate foundation movement. These cracks may appear when one part of the house’s foundation moves or settles more than another.
Solution:
If you suspect foundation movement, consult a structural engineer to assess and stabilise the foundation.
3. Diagonal Cracks
These cracks are often due to differential settlement or uneven load distribution. They typically indicate that structural elements of the building are under stress.
Solution:
In such cases, it is important to strengthen the affected structural parts before repairing the plaster.
Effective Solutions for Repairing Cracks
Step 1: Diagnose the Root Cause
Before any repair, it is critical to determine the underlying cause of the crack. Otherwise, any repairs made may be temporary and the crack may reappear.
Step 2: Prepare the Surface
Clean the cracked area thoroughly by removing any loose plaster and debris. Ensure the surface is free from moisture and contaminants.
Step 3: Apply Cement-Based Fillers
Use a cement-based filler to fill in the crack. This is especially effective for smaller hairline cracks and minor damage.
Step 4: Reinforce Major Cracks
For larger or structural cracks, you may need to insert a reinforcement mesh to provide added strength. After reinforcing, cover it with plaster and allow it to cure properly.
Step 5: Consult Professionals
For significant structural issues, it’s advisable to consult with construction experts or structural engineers to ensure the cracks are addressed comprehensively.
Conclusion
Cracks in cement plaster are caused by a combination of factors, ranging from poor construction practices and water damage to temperature fluctuations and foundation movement.
By identifying the root cause of the crack and taking preventive measures during construction, you can significantly reduce the chances of cracks forming.
Taking proactive steps, such as ensuring proper surface preparation, using the correct cement-to-sand ratio, and addressing any foundation issues, can help maintain your walls in excellent condition.
Frequently Asked Questions
Can Cement Plaster Cracks Be Caused By Poor Workmanship?
Yes, poor workmanship can contribute to cracks in cement plaster.
Improper mixing of materials, incorrect application techniques, and insufficient thickness of the plaster can all lead to cracking.
It is essential to ensure that the plaster is applied evenly, with proper thickness and appropriate bonding with the underlying surface.
Which Environmental Factors Cause Cement Plaster Cracks?
Environmental factors can have a significant impact on the development of cracks in cement plaster.
Changes in temperature and humidity levels can cause the plaster to expand or contract, leading to cracks.
Additionally, exposure to excessive moisture, such as rain or water leakage, can weaken the plaster and make it more susceptible to cracking.
What Are Cement Plaster Crack Types?
Various types of cracks can occur in cement plaster, including shrinkage cracks, settlement cracks, thermal cracks, structural cracks, and hairline cracks.
Each type has different causes and characteristics, but they all indicate potential issues with the plaster or the underlying structure.
Can Cement Plaster Crack Without Reinforcement?
Yes, a lack of proper reinforcement can contribute to cracks in cement plaster.
Without adequate reinforcement, the plaster may not have enough tensile strength to withstand structural movement or external stresses, resulting in cracks.
Using reinforcing materials like metal lath or fiberglass mesh can help prevent such cracks.
How Does Structural Settling Impact Cement Plaster Cracks?
Structural settling refers to the gradual sinking or shifting of a building over time. As the structure settles, it can cause stress and movement in the plaster, leading to cracks.
Adequate foundation design and construction, as well as regular monitoring of any signs of settlement, can help prevent or mitigate such cracks.
