What effect do defoamers have on the performance of gypsum self-leveling mortar?

Defoamers are generally used only in model plaster, precision casting plaster, and self-leveling plaster mortar to reduce porosity on the surface of plaster products. Commonly used defoamers include organic compounds such as n-butanol, polyethylene glycol, and tributyl phosphate.

During construction, air bubbles often form when dry powder is mixed with water, affecting the product’s appearance. Adding an appropriate amount of dry powder defoamer can effectively eliminate air bubbles and pinholes in dry powder mortar products, as well as air holes and cavities generated during scraping and spraying, and can also improve the product’s impermeability and increase its strength.

The typical usage of dry powder defoamer is between 0.2% and 0.5%.

The presence of a suitable number of uniformly distributed, closed, stable small air bubbles in mortar significantly improves its freeze-thaw resistance, abrasion resistance, durability, and shrinkage resistance. However, uneven or unstable air bubbles not only make the surface of self-leveling mortar rough but also greatly affect its strength and other properties. Choosing a suitable defoamer can accelerate the breaking and elimination of unstable large air bubbles, making the bubbles more uniform and thus improving the mortar’s performance. This is because defoamers are also surfactants; they not only eliminate air bubbles in mortar but also act as bubble stabilizers. A dosage of 0.5% for this type of defoamer is appropriate.

Adding defoamers to gypsum-based self-leveling mortar systems can increase the fluidity of the mortar, improve its appearance after hardening, and increase its wet density, thereby significantly improving the compressive and flexural strength of the hardened self-leveling mortar.

Currently, the powder defoamers used in mortar products are mainly imported composite defoamers. Different brands of defoamers have varying suitability for the same mortar product, leading to differences in the mortar’s performance. Selecting a suitable defoamer for mortar products requiring defoaming can greatly improve the overall performance of the mortar.