If you’ve started noticing cracks in your plaster walls, you may wonder how to repair such problems.

Plaster walls can crack for numerous reasons, from structural problems to poor application techniques. Identifying the cause of cracks in your plaster can be the key to resolving the issue quickly.

In this article, we cover the basics of how to identify the cause of plaster wall cracks, the different types of cracks, and how to fix them.

Read on to discover how to apply Durham’s Water Putty to plaster wall cracks in your property!

What Causes Plaster Walls to Crack?

Plaster walls can crack due to many reasons, each linked to different underlying causes related to the material properties of plaster, environmental factors, and structural issues. Understanding these causes can help diagnose and address the problem effectively.

In general, there are six main culprits behind cracks in plaster walls:

1. Settlement and Structural Movement:  As a structure ages, it can undergo slight shifts and movements due to the settling of the foundation. This movement, even if minor, can cause stress on the plaster, leading to cracks. Structural changes, such as additions or modifications to the building, can also introduce new stresses that cause plaster to crack.
2. Temperature and Humidity Fluctuations: Plaster is sensitive to changes in temperature and humidity. When the air is humid, plaster can absorb moisture and expand. Conversely, in dry conditions, it can lose moisture and contract. These constant cycles of expansion and contraction create stress within the plaster, often leading to the formation of cracks over time.
3. Poor Application Techniques: Improper application of plaster can also be a significant cause of cracking. If the plaster mix is not prepared correctly or applied too thickly in one coat, it may not adhere properly to the substrate. Additionally, inadequate curing time between layers or poor bonding to the underlying material can result in weak spots that are prone to cracking.
4. Vibrations and External Impacts: External factors such as vibrations from nearby construction activities, heavy traffic, or even regular household activities like slamming doors can create stress on plaster walls. Over time, these repeated vibrations can lead to the development of cracks.
5. Shrinkage: Plaster naturally shrinks as it dries. If the plaster mix contains too much water or if it dries too quickly due to high temperatures, the shrinkage can be more pronounced, leading to cracks. This often results in hairline cracks on the surface of the plaster.
6. Age: The age of the plaster plays a role in its integrity. Older plaster can become brittle and lose its elasticity, making it more susceptible to cracking under stress. Regular wear and tear over decades can contribute to the development of cracks.

Different Types of Plaster Cracks 

Cracked plaster can be a common issue in both commercial and residential buildings. 

When you notice cracks in your plaster walls, it can be important to know what kind of cracks are occurring and their underlying causes. Here’s an overview of the four main types of plaster cracks:

1. Structural Cracks

Structural cracks often indicate underlying problems with the building’s foundation or structural elements. These cracks can result from the settling of the foundation, shifts due to soil movement, or other significant structural stresses. Characteristics of structural cracks include:

• Width and Continuity: Structural cracks are usually wide and continuous. They may run across walls, ceilings, and floors.
• Pattern: These cracks often follow a diagonal or stair-step pattern, particularly around windows, doors, or corners where the structure is weakest.
• Movement: Structural cracks can change over time, growing in length, width, or severity as the underlying issues worsen.

Addressing structural cracks often requires professional intervention to assess and stabilize the foundation or structural components, ensuring the long-term safety and integrity of the building.

2. Non-Structural Cracks

Non-structural cracks are typically less severe than structural cracks and are often cosmetic. They can result from minor issues such as shrinkage, thermal expansion, or minor settling. Characteristics of non-structural cracks include:

• Width: Non-structural cracks are generally narrower and less extensive than structural cracks.
• Location: These cracks are often found in plaster walls or ceilings and do not usually extend into structural elements.
• Pattern: They may appear as vertical or horizontal lines and are often localized rather than widespread.

Non-structural cracks can usually be repaired with simple patching and repainting. However, it is important to monitor them to ensure they do not develop into more serious issues over time.

3. Hairline Cracks

Hairline cracks are very fine cracks that often occur in the plaster surface. These cracks are typically the result of minor shrinkage or settling and are usually not a cause for concern. Characteristics of hairline cracks include:

• Width: Hairline cracks are very narrow, often less than 1 mm wide.
• Appearance: These cracks can appear as random, fine lines across the plaster surface.
• Location: Hairline cracks are usually superficial and do not penetrate deeply into the plaster.

Repairing hairline cracks involves filling them with a suitable filler or compound and then repainting the surface. These cracks are primarily a cosmetic issue and do not indicate structural problems.

4. Defect-Caused Cracks

Defect-caused cracks arise from issues related to the application or composition of the plaster. These defects each cause different types of cracks and include:

• Debonding: This occurs when the plaster loses adhesion to the underlying surface, leading to cracks and separation. Poor surface preparation or incorrect plaster mix can cause debonding.
• Grinning: Grinning refers to the visibility of the underlying substrate or mesh through the plaster, often resulting from uneven application or insufficient plaster thickness. This can lead to fine cracks along the visible lines.
• Expansion: Expansion cracks occur due to thermal expansion and contraction, especially if there are significant temperature fluctuations. Poorly installed plaster can exacerbate this issue.
• Popping: Popping happens when small particles within the plaster expand or contract, creating small, localized cracks or bulges. This can result from impurities or improper mixing.

Addressing defect-caused cracks typically involves correcting the underlying application issues. This may include removing the affected plaster, properly preparing the surface, and reapplying plaster with the correct technique and materials.

Tools & Materials for Fixing Cracks

Fixing plaster wall cracks requires a range of specific tools and materials to ensure a durable and visually seamless repair. The essential tools and materials you need to patch up plaster cracks include: 

• Utility Knife or Scraper: These are essential for widening and cleaning out cracks to remove any loose or crumbling material, ensuring that the filler adheres properly to a stable surface.
• Putty Knives: Putty knives come in various sizes and are used to apply plaster or filler into cracks. A narrower knife can be used for small cracks, while a wider knife is best for larger areas.
• Sandpaper or Sanding Block: Sanding supplies are crucial for smoothing the surface of the filler once it has dried, blending the repair with the surrounding wall.
• Brush or Vacuum: A brush or vacuum is needed to remove dust and debris from the cracks and surrounding area before applying any filler.
• Mixing Bucket and Stick: If using a powdered filler or plaster that requires mixing, a sturdy mixing bucket and stick are necessary for preparing the material to the right consistency.

• Choose Your Filler: Depending on the size and depth of the crack, choose the appropriate filler. Joint compound is ideal for smaller cracks, while plaster is better suited for more extensive or deeper repairs. Water putty is also a good option commonly used to repair holes, cracks, and other imperfections in plaster. 
• Fiberglass Mesh Tape: For wider or structural cracks, this tape reinforces the repair, providing additional strength and preventing the crack from reappearing.
• Primer: A primer prepares the repaired area for painting, ensuring good adhesion of the paint and uniformity in texture and color.
• Paint: Select paint that matches the existing wall color and finish to blend the repaired area seamlessly with the rest of the wall.

Having the right tools and materials is critical for successfully repairing plaster wall cracks, ensuring that the repair is not only functional but also aesthetically pleasing.

Step-by-Step Guide to Fixing Plaster Wall Cracks

To fix plaster wall cracks effectively using Durham’s Water Putty, follow these steps:

1. Clean the Crack & Prepare Your Materials: Use a utility knife to widen the crack slightly, creating a V-shaped groove. This ensures that the filler adheres well. Remove any loose debris or dust from the crack and surrounding area using a brush or vacuum. Prepare the filler you have chosen for your plaster repair project and make sure all of your supplies are on hand.
2. Apply Durham’s Water Putty: Use a putty knife to spread Durham’s into cracks and cavities of plaster walls. Durham’s Water Putty does not shrink so the cracks disappear. Plus, your repair will last and last. Using a putty knife, apply Durham’s into the crack. Ensure the filler is pressed deeply into the groove. Smooth the surface with the putty knife, removing any excess material. For deeper cracks, apply in layers, allowing each layer to dry before adding the next.
3. Sand the Surface & Prime for Painting: Once the filler is completely dry, sand the repaired area smooth, blending it with the surrounding wall surface. Apply a coat of primer to the repaired area to prepare it for painting and ensure the paint adheres well.
4. Paint the Repaired Wall: Paint the repaired area with matching paint to blend it seamlessly with the rest of the wall. Make sure to use paint that is safe for indoor use and use the proper materials, such as a drop cloth and a breathing mask. 

Plaster vs. Drywall Cracks 

Plaster and drywall cracks, while both indicative of issues within wall surfaces, differ significantly in their characteristics, causes, and repair methods. Here’s an overview of the differences:

• Material Composition: Traditional plaster walls are composed of layers of wet plaster applied over wooden laths or metal mesh. Plaster is more rigid and less forgiving than drywall, while drywall is more flexible and easier to install.
• Crack Characteristics: Plaster cracks tend to be more varied, including hairline cracks, crazing (a network of fine cracks), and larger structural cracks. They can appear due to the age of the material, settlement, or moisture issues. Plaster cracks often follow irregular patterns. Typically, drywall cracks are straight and often appear along seams where two drywall sheets meet. They are usually caused by building movement, settling, or improper installation.
• Common Causes: Age-related brittleness, structural movement, moisture infiltration, and poor application techniques can lead to plaster cracks. Drywall cracks are often due to expansion and contraction, settlement of the building, temperature changes, or improper taping and mudding during installation.
• Repair Methods: Repairing plaster cracks usually involves cleaning out the crack, applying mesh tape for reinforcement, and using a plaster compound to fill the gap. Drywall crack repair often includes taping the crack, applying joint compound, and sanding it smooth before painting.

Choose Durham’s Water Putty for Your Plaster Repair Needs

Durham’s Water Putty can be used for a wide range of different repairs, including cracked plaster. Shop Durham’s today to find the right products for your repair project.