5 Reasons for Cracks in Walls: Why Flexible Putty Is the Ideal Solution

Cracks in walls are a common issue in construction. If you look closer at the buildings around you or even your home, you might easily spot some wall cracks. These cracks may run horizontally or vertically, but what are the reasons for cracks in walls?

Types of Cracks in Walls

Wall cracks can be primarily categorized into two types: structural cracks and non-structural cracks.

Structural cracks in walls are typically caused by changes in the building’s structure, such as foundation settlement, earthquakes, or insufficient load-bearing capacity. These cracks are usually wide, irregular in shape, and pose significant safety hazards.

Non-structural cracks generally result from material properties or construction-related issues. They do not compromise the structural integrity or safety of the building.

Next, we will focus on analyzing the reasons of non-structural cracks in walls.

What are the Causes of Cracks in Walls?

1. Dry Shrinkage Cracks

Wall surfaces are typically made of cement mortar or plaster. During the drying process, these materials shrink, resulting in small cracks on walls. This dry shrinkage effect is one of the most common causes of cracks in walls. As cement-based materials lose moisture during curing, their volume decreases, leading to cracks in walls.

2. Thermal Expansion and Contraction

Temperature fluctuations can also cause wall cracks. Building materials expand when heated and contract when cooled. This constant movement creates stress within the wall, eventually forming cracks. This effect is especially noticeable in regions with significant temperature differences.

3. Moisture Expansion and Contraction

Humidity changes can also impact wall stability. When wall materials absorb moisture, they expand, and when they dry out, they contract. This repeated moisture cycle can cause cracks, particularly in humid environments.

4. Material Characteristics

Ordinary putty lacks sufficient elasticity to accommodate wall movements. When the base layer of the wall cracks or shifts, ordinary putty coatings cannot stretch accordingly, causing cracks to appear on the surface.

5. Poor Construction Quality

Improper application during construction can also lead to cracks. Factors such as inadequate surface preparation, incorrect material ratios, or unsuitable environmental conditions during application increase the risk of wall cracks.

How to Fix Wall Cracks?

Using flexible putty is an effective solution that addresses the root cause of the problem. No matter what reasons for cracks on walls, applying flexible putty is always a wise choice.

Flexible wall putty can undergo significant deformation, absorbing the tensile stress exerted on the putty film and paint layer caused by mortar shrinkage. When cracks appear in the wall’s base layer, the flexible putty film stretches and conceals the cracks, preventing them from reaching the surface. Additionally, the elastic recovery of flexible putty helps reduce crack expansion, maintaining the wall’s appearance and integrity.

Before applying putty to the wall, use flexible putty to level and coat the surface.

How to use:
After filling the cracks and sanding the surface smooth, use a scraper or roller to evenly apply flexible putty. This ensures a smooth and even wall surface, providing a solid foundation for subsequent paint application.

If cracks have already appeared on the wall, use flexible filler putty or flexible repair putty to fill or repair them.

How to use:
First, clean the cracks to remove dust and loose materials. Then, use a scraper or filling tool to apply the putty into the cracks, smooth it out, and let it dry completely before sanding.

 

In addition to wall repair, flexible putty can also be used for repairing wooden surfaces. Flexible wood putty is ideal for filling common defects in furniture, doors, windows, and wooden products, such as cracks, wormholes, and nail holes.

How Flexible Putty Protect Wall from Cracking

The key lies in the putty’s ability to deform and absorb tensile stress caused by mortar or plaster shrinkage.

When the mortar layer shrinks, the cracks widen, and the flexible putty film is stretched along the base layer. Since tensile stress decreases gradually throughout the putty’s thickness, the elastic recovery force of the putty minimizes deformation.

If the deformation is absorbed by the flexible putty layer, the rigid paint film on top will remain intact without cracking.

 

If the deformation exceeds the putty’s capacity to absorb stress, the rigid paint film may crack.

In simple terms, flexible wall putty acts like a “shock absorber” or an “elastic coat” for walls. When hair line cracks form due to temperature changes, humidity shifts, or material shrinkage, flexible wall putty helps the wall adapt to these changes, preventing cracks from reaching the surface and ensuring a smooth, attractive finish.

Flexible Putty Formulation

(1) Key Design Principles

Wall putty can be seen as a highly viscous coating, but this viscosity is not solely achieved through thickening agents; instead, it relies on a high solid content. As a result, the formulation principles for putty are similar to those for paint.

Unique Features of Flexible Wall Putty Composition:

1️⃣High Thixotropy: Flexible putty must have a thick, paste-like consistency with high viscosity to ensure it can be applied with a flexible putty knife without sagging.

2️⃣Low or Near-Critical Pigment Volume Concentration (PVC): To achieve high tensile strength and elongation at break, the pigment volume concentration should be lower than or close to its critical PVC. This is a key distinction between flexible putty and ordinary putty, which typically has a PVC above 80%.

3️⃣Elastic Binder: The film-forming material used in flexible wall putty must be an elastic construction emulsion, rather than a standard construction emulsion with a high glass transition temperature.

4️⃣Water Retention Agents: To ensure easy application and proper curing, flexible putty should include water-retaining thickening agents.

In practice, although wall putty composition follows similar principles to paint design, it is often guided more by experience due to lower performance requirements. Typically, the process involves developing a base formula or referencing existing formulas, followed by multiple trial adjustments until the desired performance is achieved.

(2) Basic Formula for Two-Component Flexible Putty (Two Part Putty With Flexibility)

Flexible putty requires not only flexibility but also high tensile strength, adhesion strength, and water resistance. Therefore, a two part formulation is recommended. This method allows the use of cement to enhance the water resistance of the putty film while resolving the conflict between paste products that cannot include cement and powder products that rely on expensive redispersible polymer powder.

Table 1-1 Reference Formula for Two-Component Flexible Putty with Polymer Emulsion and Cement

(3) Formula Explanation

The polymer component is the key material that determines the flexibility of the putty film. If the polymer content does not reach a certain level, the crack resistance of the putty film will fail to meet standard requirements.

The defoamer plays an important role in the formula, as it helps prevent air bubbles from forming within the putty film. Since water is added to the polymer emulsion, the concentration of the original preservative in the emulsion decreases. Therefore, additional preservative is required to ensure the liquid material remains mold-free during storage.

Adding cellulose ether to the powder component can reduce the mold prevention requirements for the liquid component. Flexible putty requires a polymer emulsion with a low glass transition temperature. As a result, no film-forming agent is needed in the liquid component. However, to ensure the stability of the liquid material when stored at low temperatures, an antifreeze agent (freeze-thaw stabilizer) is still necessary.

For walls that need strong resistance to chemicals and weather, you can directly use flexible epoxy putty. It’s tougher and handles pressure better than regular flexible putty. Even in extreme conditions like humidity, high heat, or freezing cold, it stays reliable and resists cracking effectively.

Conclusion

In summary, wall cracks primarily result from factors such as dry shrinkage, thermal expansion and contraction, moisture-related expansion and contraction, material properties, and construction quality.

Using flexible putty is an effective solution to causes of wall cracks in building, as its elastic deformation can absorb stress changes within the wall, preventing cracks from spreading to the surface coating.

When designing a flexible putty formula, key factors such as high viscosity, tensile strength, and water resistance must be considered. By carefully adjusting the polymer emulsion content and formulation, the flexibility and adhesion strength of the putty film can be effectively improved.

You can use the flexible putty formula mentioned above to make wall putty with flexibility. By adding professional additives (like those from WOTAIchem – China’s top putty additive maker), you’ll boost its flexibility and stop cracks from forming on walls.

WOTAIchem specializes in high-quality products like redispersible polymer powder, defoamers, and cellulose ether to upgrade your putty’s performance in every way. Contact us now for free samples!