Inorganic Zinc-rich Paint Application Details:
Surface Treatment
Before sandblasting, structural steel must be pre-treated, including welding seam smoothing, additional welding, burr and edge hole sanding, spatter removal, and sharp edge chamfering to ensure adequate contact between zinc powder and the steel surface while maintaining good conductivity. The steel surface must be sandblasted to SA2.5 (ISO 8501-1:1988) for resistance. The roughness should reach Rugotest No3, BN10a, and Keen-Tato surface comparison samples, with a g/s limit of 3.0 or ISO/DIS 8503-1 coarse intermediate (g). Insufficient roughness can affect adhesion and increase the likelihood of paint film cracking. Steel grit, silica-alumina, and other oil-free, water-free, and dirt-free abrasives can be used. The steel grit particle size is 0.8-1.2mm, and the silica-alumina particle size is 0.4-1.8mm, which can produce a good surface roughness effect. The nozzle pressure requirement is 6-7bar/85-100psi. Dusting should be done immediately after sandblasting, and some stubborn particles can be brushed off with an iron brush.
Painting Techniques
The inorganic zinc-rich paint series can be applied using airless and air spray methods. Roll coating is not suitable, and brush application is only used for small area repairs.
Air Spray
Air spray assists in reducing dry spray, though it applies at a slower pace. By experience, adding 15-20% thinner during air spraying is appropriate. It aids in smoothing the paint film and minimizing paint mist. Air spraying is particularly suitable for water-soluble inorganic zinc-rich coatings. When topping off, the spray gun should be cleaned intermittently to prevent clogging. Pressure: 3-4 kg/cm², nozzle: 1.8-2mm.
2. Airless Spray
Airless spray painting offers high efficiency but is prone to dry spray. Requires low pump pressure, such as 30:1 and 45:1 paint pumps. Use a 60-80 mesh filter. Depending on the spraying process, add 10-20% thinner as needed. Excessive thinner can reduce film thickness or cause runs. Suitable for complex structures.
3. Opt for the use of small-bore nozzle construction techniques.
To ensure even coating, the double-coating method can be employed, which involves applying the second coat within 15-30 minutes after the first coat has dried and darkened. Apply the paint film. When using this method, it must be thinned to about 15% to avoid excessive thickness. If the paint film at the corner welds is too thick, use a flat brush about 2.5cm wide. If the working conditions between paint layers require several hours, ensure the relative humidity is kept at a low level of 60%. Any dry-sprayed paint film must be scraped off with a scraper, and edges must be sanded or gently abraded with sandpaper. A single thin spray of 30% thinned paint should be applied.
Paint Packaging
4. The zinc powder can be mixed with the liquid components before or after spraying, while stirring. Do not reverse the process. It is prone to clumping when the liquid components are added to the zinc powder, and uneven stirring may occur.
