Problems and solutions related to cellulose in putty powder use (Part 2) - HPMC-PVA

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Bubbling and Pinholes After Application

Problem: Numerous tiny air bubbles or pinhole-like pits appear on the surface of the putty layer.

Core Causes:

High Cellulose Viscosity:High-viscosity cellulose makes it difficult for air trapped in the putty to escape.

Improper Substrate Preparation: The substrate (such as cement mortar walls) is too rough, porous, or dry, absorbing water too quickly. During application, air is forced into the pores and cannot escape.

Improper Application Method: Applying a single coat too thickly, or finishing at the wrong time (finishing after the surface has skinned but internal air is still being released).

Solutions:

Adjust Formula Viscosity: Refer to point one and choose cellulose with a moderate viscosity.

Proper Substrate Preparation: Before applying putty, the substrate must be sealed and cured with a wall primer (concrete interface agent) to prevent rapid water absorption and air release.

Improve Application Process: Follow the principle of "thin coats, multiple layers." The first coat is mainly for leveling and covering; apply the second coat after the surface is dry. Finishing is performed when the putty slurry is "finger dry" (the surface water film disappears, but it is not yet fully hardened), at which point the gas has been mostly expelled.

Putty Layer Powdering and Low Strength

Problem: After drying, the putty has low surface strength and powders easily when touched.

Core Cause: Insufficient water retention leads to incomplete hydration of cement/lime lime: This is an indirect manifestation of cellulose problems. Cement or lime lime requires sufficient moisture and time to complete the hydration reaction and develop strength. If the cellulose has poor water retention, the moisture is absorbed too quickly by the substrate or air, interrupting the hydration reaction and preventing strength formation.

Impurities in the cellulose itself: Some inferior cellulose contains impurities such as salts, which interfere with the hydration of cementitious materials.

Solutions: Fundamentally solve the water retention problem: Ensure the use of sufficient quantity of high-water-retention, high-quality cellulose.

Check cementitious materials: Ensure the quality and amount of cement or lime lime added are sufficient.

Strictly prohibit excessive use of PVA (polyvinyl alcohol): Some installers or manufacturers add PVA to increase initial tackiness, but excessive PVA will seriously affect the final strength and increase the risk of powdering.

Poor dissolution, resulting in "prickly heat" or "fish eyes"

Problem: Undissolved cellulose gel particles appear in the mixed putty slurry, forming transparent, granular bumps on the wall surface after application, commonly known as "prickly heat."

Core Cause:

Poor cellulose dispersibility or clumping upon contact with water: During putty powder production or on-site mixing, the cellulose was not evenly dispersed and quickly clumped together upon contact with water, forming a gel film that encapsulates the dry powder inside, preventing dissolution.

Insufficient mixing: Insufficient mixing time or speed during application.

Solutions:

Improve production process: During production, premix the cellulose with a large amount of powder (such as heavy calcium carbonate), or use a mixer with high-efficiency dispersing capabilities.

Sufficient mixing: During application, an electric mixer must be used. After mixing, let it stand for 2-3 minutes (called "resting"), then lightly mix again to ensure the cellulose is fully dissolved and hydrated.