Cracks appearing after plastering can be concerning for many builders and homeowners alike.
It’s natural to wonder if these cracks are a sign of poor workmanship or a more significant issue.
However, in many cases, cracks after plastering are quite normal and can occur due to several factors.
In this article, we will explore the causes of plaster cracks, the different types of cracks, and the steps you can take to prevent or fix them.
Let’s get straight to the point
Cracks after plastering are common and often not a major concern. They can be caused by factors such as temperature fluctuations, poor plaster mixes, insufficient drying time, or structural movement.
There are various types of cracks, such as hairline, horizontal, vertical, and diagonal, which can indicate different issues.
Most cracks are cosmetic (non-structural) and can be repaired, but some, like structural cracks, may require professional attention.
Preventing cracks involves using proper plaster mixes, allowing adequate drying time, and reinforcing weak areas. Repairing cracks is straightforward with tools like joint compound and mesh tape.
What Causes Cracks After Plastering?
Temperature and Humidity Fluctuations
In Australia, with its varying climate conditions, fluctuations in temperature and humidity can cause plaster to crack.
When the plaster dries too quickly due to high temperatures, it may not cure properly, leading to the formation of cracks. Similarly, in humid conditions, excessive moisture in the air can affect the drying process.
Poor Plaster Mix
An improper plaster mix is another common cause of cracks. If the ratio of water to plaster is incorrect, the plaster can become too weak or too dry, leading to shrinkage and cracking as it sets. It is essential to follow the manufacturer’s instructions to ensure the right mix.
Insufficient Drying Time
Rushing the drying process can result in cracks. Plaster requires sufficient time to cure properly.
If painted or worked on before it fully dries, the plaster may crack as it continues to shrink and settle. It’s important to give the plaster adequate time to dry.
Structural Movement
Cracks can also occur due to structural movement within the building. In older homes, or where there has been recent construction or renovation work, shifts in the foundation or movement in the walls can cause cracks to appear in plastered surfaces.
Types of Cracks After Plastering
After plastering, various types of cracks can develop, and each type may indicate a different issue. Understanding these cracks will help you determine whether they are a normal part of the plastering process or a sign of a more serious problem.
Hairline Cracks
Hairline cracks are the most common type of cracks that appear after plastering. These are typically very thin and are less than 1.5mm wide.
They are usually caused by the natural settling of the plaster as it dries or by changes in temperature and humidity.
While these cracks are often considered cosmetic, they should still be repaired to prevent further damage.
Horizontal Cracks
Horizontal cracks usually appear as straight lines running parallel to the floor. These cracks may occur if the plaster has not adhered properly to the surface or if there has been structural movement
. It’s essential to monitor horizontal cracks, as they can lead to more significant issues if ignored.
Vertical Cracks
Vertical cracks typically run from the ceiling to the floor and may indicate settling within the building’s structure.
Like horizontal cracks, these should be inspected carefully, as they may be a sign of underlying structural problems.
Diagonal Cracks
Diagonal cracks can appear due to a poor plaster mix, improper application, or structural movement.
These cracks are less common but can be an indicator of a more severe issue, especially if they widen over time.
Structural vs Non-Structural Cracks
Cracks in plaster can be classified into two main categories: structural and non-structural cracks.
Structural Cracks
Structural cracks are more severe and may indicate significant problems within the building’s framework.
These cracks can result from poor workmanship, natural settlement, or foundation movement.
If you notice large cracks that continue to grow, it’s important to consult a professional, as they may require more extensive repairs.
Non-Structural Cracks
Non-structural cracks are often caused by temperature changes, improper curing, or poor materials.
These cracks are usually cosmetic and can be repaired without significant concern. However, if left unaddressed, even small cracks can allow moisture to enter, leading to more significant problems down the road.
Common Causes of Cracks in Plaster
Moisture Loss (Shrinkage Cracks)
When plaster loses moisture too quickly, it can lead to shrinkage cracks. This is especially common in hot Australian climates where high temperatures speed up the evaporation process. The plaster loses moisture rapidly, causing it to shrink and crack.
Poor Workmanship and Structural Defects
Poor workmanship during the plastering process can also cause cracks. For example, failing to apply a chicken mesh in high-stress areas or not properly sealing joints can lead to cracking as the plaster dries.
Silt and Fine Sand in the Plaster Mix
The quality of the sand used in the plaster mix plays a crucial role in preventing cracks. If the sand contains too much silt, it can draw water away from the plaster during the curing process, leading to drying and cracking.
Natural Disasters
In areas prone to earthquakes, floods, or high winds, cracks may develop in the plaster due to structural movement caused by these natural events. In such cases, the cracks may be more significant and indicate damage to the building’s structure.
Temperature Changes (Thermal Cracks)
Thermal cracks occur when there is a significant fluctuation in temperature between day and night. The plaster surface heats up during the day and cools down at night, causing the plaster to expand and contract, which can lead to cracks over time.
How to Prevent Cracks After Plastering
Preventing cracks in freshly plastered walls requires careful preparation and proper techniques. Here are some tips to ensure a smooth, crack-free finish:
Ensure a Stable Foundation
Before applying plaster, make sure the substrate is stable and free from defects. Repair any existing cracks, holes, or weak spots in the wall to create a solid foundation for the plaster to adhere to.
Use the Proper Plaster Mix
Always follow the manufacturer’s guidelines for mixing plaster. Ensure the correct ratio of water to plaster to achieve the right consistency, which will help prevent shrinkage and cracking.
Apply Plaster Evenly
When plaster is applied unevenly, it can create stress on the surface, leading to cracks. Use the right tools, such as a straight edge or plastering trowel, to ensure an even layer.
Allow Adequate Drying Time
Don’t rush the drying process. Allow the plaster to dry fully before proceeding with painting or any other work. This will give the plaster enough time to set correctly and reduce the risk of cracking.
Consider Using Reinforcing Mesh
For areas prone to movement, such as around windows and doors, consider using reinforcing mesh to help prevent cracks. The mesh adds strength to the plaster and helps distribute stress evenly.
How to Fix Cracks in Plaster
If you already have cracks in your plaster, don’t worry. In most cases, they can be repaired with some simple tools and materials.
Step-by-Step Guide to Fixing Plaster Cracks
- Clean the crack: Use a utility knife to remove any loose plaster, debris, or dust from the crack.
- Apply joint compound: Fill the crack with a thin layer of joint compound, working it into the crack with a putty knife.
- Use mesh tape: Cover the crack with mesh tape and press it gently into the compound.
- Apply another coat of compound: Spread a second layer of joint compound over the tape and smooth it out.
- Sand the area: Once the compound is dry, lightly sand the area to create a smooth surface.
- Repeat if necessary: For deeper cracks, you may need to apply a third coat of compound and sand again to ensure a flawless finish.
Fixing Hairline Cracks
Hairline cracks can be repaired with a flexible patching compound. Clean the crack, apply the compound, and smooth it out with a putty knife. There’s no need to sand in this case, as the compound is designed to remain flexible and prevent further cracking.
Conclusion
While cracks after plastering are common, they can usually be prevented or repaired with proper techniques and materials. Temperature fluctuations, poor plaster mixes, and insufficient drying time are just a few reasons why cracks may appear.
Understanding the causes of cracks and how to fix them is essential for maintaining the integrity and appearance of your walls.
Whether you are a builder or a homeowner, addressing cracks early can help prevent more significant issues and ensure your plastered walls remain smooth and strong for years to come.
Frequently Asked Questions
Can Cracks After Plastering Be Prevented?
Cracks after plastering can be prevented by ensuring that the plaster is applied evenly and in thin layers, allowing sufficient drying time between each layer, and using the appropriate type of plaster for the plastered surface.
It is also important to address any underlying issues, such as moisture or structural problems, before applying plaster. Regular maintenance and monitoring of the building can also help prevent cracks from developing.
How Do I Know If The Cracks After Plastering Are Serious?
The seriousness of cracks after plastering can vary depending on the size, location, and type of crack. For example, hairline cracks are generally not a cause for concern, while wider and deeper cracks may indicate a larger structural issue that requires immediate attention.
However, suppose the cracks continue to expand, or there are signs of other damage, such as bulging or sagging. In that case, consulting with a professional to assess the situation and determine the appropriate course of action is recommended.
How Long Does It Take For Cracks To Appear After Plastering, And Can They Be A Sign Of A Larger Problem With The Structure Of The Building?
Cracks after plastering can appear within a few days or up to several weeks after the plaster has been applied, depending on factors such as the type of plaster used, the environmental conditions, and the underlying structure of the building.
While some cracking is normal, excessive cracking or cracks that continue to expand may indicate a larger problem with the building’s structure, such as settling, shifting, or moisture damage.
Therefore, consulting with a professional to assess the situation and determine the appropriate course of action is recommended.
Can The Appearance Of Cracks In Plaster Be Minimised Through Regular Maintenance Or Preventative Measures?
Yes, regular maintenance and preventative measures can help minimise the appearance of cracks in plaster.
Keeping the building’s environment stable by controlling temperature and humidity levels and addressing any underlying structural issues can help prevent cracking.Â
Regular inspections and maintenance can identify potential issues early on and prevent them from becoming larger problems.
Additionally, using the appropriate type of plaster for the specific surface being plastered and applying it evenly in thin layers with sufficient drying time between each layer can help minimise cracking.
Are There Any Instances Where Cracks In Plaster Should Be Cause For Concern, And When Should A Professional Be Consulted To Assess The Situation?
Yes, there are instances where cracks in plaster should be cause for concern, such as when they are wide, deep, or expand over time.
However, cracks accompanied by other signs of damage, such as bulging, sagging, or moisture, may also indicate a larger problem with the building’s structure.Â
In these cases, it is recommended to consult a professional to assess the situation and determine the appropriate course of action.
A professional can help identify the cause of the cracking and determine whether it is a cosmetic issue or a more serious structural problem that requires immediate attention.
