How to Prevent Surface Cracking and Delamination of Lime-Based Putty Powder During Low-Temperature Grinding
Release Time:
2022-01-12
Source:
How to Prevent Surface Cracking and Delamination of Lime-Based Putty Powder During Low-Temperature Grinding
Putty formulated with hydrated lime powder as the inorganic binder boasts high whiteness and can achieve a mirror-like finish, thereby meeting consumers’ growing demand for more aesthetically pleasing wall finishes. However, due to its high rigidity and low flexibility, lime-based putty exhibits poor resistance to self-cracking; it is typically applied as a topcoat over gypsum-based substrates to enhance visual appeal. Moreover, because of its fine texture, it is widely used as a finishing-layer putty material.
Lime-based putty has poor water retention and is prone to peeling under repeated pressure. It also exhibits poor water resistance: when exposed to water, it easily disintegrates and bubbles; prolonged exposure to moisture can cause it to loosen, chalk, and lead to mold growth on the wall surface.
Lime-based putty is suitable for dry surfaces or dry environments; it is difficult to sand in damp, rainy weather.
Lime-based putty is highly alkaline; skin contact can easily cause erythematous rashes, allergic itching, and sanding dust can irritate the eyes.
Lime-based putty exhibits strong adhesion and a rapid increase in putty strength; however, its bond strength diminishes over time, leading to a corresponding reduction in overall strength.
How can we prevent the surface of lime-based putty powder from cracking and delaminating during low-temperature conditions?
1. The fineness of heavy calcium carbonate must be appropriate. Proper fineness ensures a smooth, fine finish when sanding.
2. It is necessary to reduce the surface hardness of the putty. When a summer formulation is used in winter, the putty surface remains exposed to atmospheric carbon dioxide under humid conditions for an extended period, resulting in a film hardness that is significantly higher than that achieved in summer. Conversely, due to the lower ambient temperature, the interior of the putty coating dries much more slowly, often yielding a hardness that falls short of the gelation-induced hardness obtained with the same formulation in summer. This disparity—too hard on the surface but too soft internally—leads to grinding-induced delamination. To address this issue, the surface hardness of the putty must be reduced by shortening the time it takes for the hydrated lime powder to harden and form a film in humid air.
First: Allow the underlying layer to dry completely before applying the next coat, so as to minimize the opportunity for the finish putty to react excessively with carbon dioxide under humid conditions.
Second: Adjust the formulation to prevent the formation of “water sheen” on the putty surface (i.e., excessive film formation and hardening). Once “water sheen” develops, the putty surface becomes excessively hard while simultaneously impeding the penetration of atmospheric carbon dioxide into the interior, resulting in insufficient internal strength and poor resistance to sanding.
3. It is necessary to enhance the internal cohesion and internal abrasion resistance of the putty.
First: Optimize the formulation to prevent the formation of a “water sheen” on the putty surface, thereby facilitating the penetration of atmospheric carbon dioxide into the putty layer, enhancing its internal cementitious strength, and improving its internal abrasion resistance.
Second: Incorporate other organic polymer compounds into the formulation to enhance internal bond strength and wear resistance.
It is best to sand lime-based putty within 48 hours.
