Eliminate putty bubbling: a comprehensive solution for HPMC cellulose from selection to construction techniques!

In the construction of putty powder, bubbling is a common issue. Factors such as the temperature during construction, the water absorption rate of the base layer, or improper mixing methods may cause bubbling in putty powder.

How can this be adjusted?

1. Optimize the mixing process

Low-speed mixing:

Utilize a low-speed mixer (300-600 rpm) to minimize air incorporation and prevent excessive bubbles that can result from high-speed mixing. 

Opt for high-quality cellulose:

Putty powder typically recommends using medium-low viscosity cellulose (such as HPMC with a viscosity of 80,000-100,000 mPa·s), which ensures water retention without causing undue thickening. Adjust the dosage according to the recommended amount (usually 0.3%-0.5%) to prevent excessive thickening.

2. Adjust the construction technique

Apply thinly and in multiple layers:

Ensure that each layer is no more than 1 to 2 millimeters thick to prevent excessive thickness, which can result in internal bubbles that cannot escape.

Scraping angle and strength:

The scraper should maintain a 60° to 70° angle with the wall, apply pressure evenly, and avoid repeated scraping back and forth (which can easily introduce air). The second scraping direction should be perpendicular to the first to minimize the accumulation of bubbles between layers.

Finishing time:

Before the putty surface begins to solidify (approximately 10 to 15 minutes after scraping), lightly press and finish to help seal the surface micro-bubbles.

Add water in stages:

Initially incorporate 70% of the water and stir, then progressively add the remaining water to ensure the material is thoroughly moistened and to minimize air entrapment from dry powder clumping.

Standing and Defoaming:

After stirring, allow the mixture to stand for 5 to 10 minutes to permit bubbles to rise and burst naturally before use. Alternatively, incorporate 0.1% to 0.3% silicone or mineral oil defoamers to directly suppress bubble formation and encourage bursting.

3. Substrate Preparation

Wetting of the Substrate:

Prior to commencement of works, uniformly moisten the wall surface with a spray bottle (ensuring no standing water remains) to prevent the substrate from absorbing moisture too rapidly, which could lead to premature drying and sealing of the putty surface, thereby inhibiting the escape of internal air bubbles.

Filling of Cavities:

Prior to application, use plaster or a coarse putty to fill in large cavities and cracks within the wall to minimize the volume of residual air.

Removal of Loose Dust:

Employ a brush to eliminate any loose dust from the wall surface to avoid the putty adhering inadequately to the substrate due to contaminants, which could result in the formation of hollows and bubbles.

4. Environmental control

Temperature and humidity:

The best construction temperature is 5~35℃, and the humidity is 40%~70%. Avoid direct sunlight on the construction surface in hot weather, and work can be done in sections.

Ventilation management:

Avoid strong ventilation within 24 hours after construction to prevent rapid water loss and crusting on the surface and seal internal bubbles.