To achieve perfect stone-like effects with water-in-sand coatings, the first step is base surface treatment and inspection. The inspection covers five key procedures. Qualified results in all five items guarantee a standard-compliant water-in-sand wall project.
1. Structural Strength
Insufficient base strength will weaken coating adhesion. A qualified base surface shall be free from powder shedding, sanding, hollowing, peeling, cracking and delamination.
2. Flatness
Uneven base surface will ruin the final decorative effect of stone-like paint. Four inspection standards are required: surface flatness, vertical internal and external corners, vertical wall surface and right-angle corners.
3. Dryness
Moisture retained in cement mortar carries alkaline substances to the surface and damages the coating. The base must be fully dried before primer spraying.
4. Alkalinity
Excessive alkalinity impairs coating adhesion and causes common defects such as discoloration, peeling, whitening and mottling. The PH value of the base shall be lower than 10.
5. Cleanliness
Remove surface laitance, dust, oil stains and other impurities to ensure firm bonding of the coating.
A well-treated base only lays a foundation for spraying construction. To create high-quality water-in-sand stone-like walls, the construction process of the coating itself is the core priority. Through long-term practical experience, experienced constructors have summed up the following practical tips:
1. Stirring
Water-in-sand stone-like coatings are packaged and delivered nationwide right after production. Precipitation may occur during long-distance transportation or long-term storage. Gently stir from the bottom evenly before use. The viscosity is well adjusted before delivery, so no water dilution is recommended.
2. Temperature
Construct at ambient temperature between 5℃ and 35℃ with relative humidity of 60% to 70%. Stop construction in rainy days and ensure no rain exposure within 24 hours after spraying. Spraying is not advised when wind force exceeds Grade 4.
3. Air Pressure
Ensure the air compressor air storage capacity is over 12kg and working air pressure reaches above 8kg. The average consumption is 1.2 to 1.5 kilograms per square meter, and 1.6 to 2 kilograms for heavy concave-convex textures. The coverage rate varies according to particle size, construction texture and base roughness. Conduct on-site coverage test before formal construction.
4. Mottling
Mottling is mainly caused by uneven spraying leading to inconsistent color between thick and thin coating areas. Adopt thin-coat multi-pass spraying for uniform finish and use matching base paint effectively.
5. Color Difference
Conduct small-area color trial spraying first and confirm consistency with standard samples before large-scale construction. Slight color difference among different batches is normal due to natural colored sand raw materials. Use materials from the same batch constructed by the same team on the same wall. Complete wall spraying continuously from top to bottom to avoid color deviation caused by intermittent work. Note color variations under direct sunlight, reflected light, backlight and different surface textures.
6. Color Difference Repair
Reserve several barrels of same-batch coatings after wall construction for later defect repair to avoid obvious color deviation. If two batches are used on one wall, apply the later batch as base layer and the former batch as surface layer for natural color transition.
7. Whitening
There are two common whitening causes. One is alkali efflorescence on concrete walls with white powder on touch. The other is whitening after topcoat finishing, which results from uneven roller coating causing topcoat accumulation in grooves. Spray finishing coat is preferred, and apply topcoat 48 hours after full drying of stone-like coating.
8. Window Sill & Platform Construction
These positions are prone to excessive one-time thick coating. Remove fallen sand and gravel thoroughly before spraying on window sills and platforms.
9. Professional Construction
Hire experienced and professional construction teams for water-in-sand coating projects.
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