Painting requirements: all parts are derusted by shot blasting. The derusting grade of shot blasting is Sa2.5, and two anti-rust primers are applied. The total thickness of dry paint film is not less than 70um.
Implementing norms and standards
Rust grade and derusting grade of steel surface before painting (GB8923- 1988)
Code for Construction and Acceptance of Building Anticorrosion Engineering (GB502 12-2002)
Determination of adhesion of paint film (GB 1720-79)
Code for Construction and Acceptance of Steel Structure Engineering (GB50205-200 1)
Technical requirements for application of fire retardant coatings for steel structures (CECS24)
Coating material requirements
Primer adopts red lead antirust paint twice; Fire retardant coatings are used for grilles. The fire resistance limit is not less than 0.5 hours.
Painting operation technology
Materials must have product test sheets, product specifications and certificates.
Materials must be marked with factory date and storage period, and expired products are prohibited.
Construction machines and tools: shot blasting machine, recycling device, spray gun, spray air pump, shovel, hand grinding wheel, emery cloth, wire brush, compressor, paint bucket and brush.
Process flow:
Before painting, the steel surface should be shot blasted to remove rust, powdery floating rust, peelable scales, oil stains, splashes and dust, until the steel surface is steel gray and the surface quality reaches the quality standard of Sa2.5, and then the dust on the steel surface should be removed with a dry brush, a clean rag or compressed air.
After the shot blasting and derusting is completed, the dust shall be cleaned within 4-6 hours and the primer shall be sprayed twice.
Preparation of coating
The batching personnel must be familiar with the performance, formula and matters needing attention of the materials.
Stir the paint evenly. If paint skin, impurity particles or coarse particles are found, they must be filtered with a wire mesh of 80 mesh or more before use.
Strictly control the curing time after batching.
Each ingredient must be used up within 4-6 hours, and then it is forbidden to use it.
Strictly control the addition of various curing agents and diluents. After the coating is cured for 12 hours, it can be delivered after passing the inspection.
Primer coating
Fully stir the paint to make it uniform in color and viscosity.
Spray the first primer, pay attention to the same spraying direction, even and tidy.
After the first primer is applied, the second primer is dried before spraying until the designed film thickness is reached.
Coating quality inspection
Derusting shall be inspected according to the color photos of Sa2.5 in Rust Grade and Derusting Grade of Steel Surface before Painting (GB8923- 1988), with a roughness of 40-75um.
According to the Method for Measuring Adhesion of Paint Film (GB 1720-79), the coating should be smooth and uniform, free of bubbles, pinholes and dust. Visual inspection should be used.
Check the thickness, each layer thickness and overall thickness meet the design requirements, and check with a thickness gauge. Inspection shall be carried out according to the Method for Measuring Film Thickness (GB 1764-79).
Adhesive tape should be attached to the coating for adhesion measurement, and the adhesive tape should be compacted. If the paint film at one end of the tape does not fall off, it is qualified, and it shall be inspected according to the Method for Measuring Adhesion of Paint Film (GB 1720-79).
Inspection quantity: each type of steel structure is randomly selected 10%, and not less than 3 pieces, with 5 points for each piece.
Topcoat painting: Topcoat will be sprayed on the construction site. Before spraying, damaged and flaked parts should be derusted and primed.
Attention should be paid to when spraying:
Adjust the nozzle diameter and spraying pressure so that the spray gun tube can freely extend to the working area.
When spraying, the distance between the nozzle and the coating should be kept good. Generally, the distance between the spray gun and the working face should be about 10 mm.
The included angle between the spray gun and the base surface of the component should be vertical, or the nozzle should be slightly inclined upward.
When spraying, the nozzles should move in parallel, with balanced movement and consistent speed to ensure uniform coating.
Fireproof coating process
After the rebar is installed in place, spray/brush fire retardant coating on the construction site.
Fire retardant coatings shall be qualified products approved by local fire departments.
Check the approval documents and factory certificate of paint.
Delineate the scope of the construction site and provide a good painting environment.
Ensure the normal use of mixers, mortar pumps, wire mesh shears, measuring containers and other machines.
Surface treatment: thoroughly remove the dust, welding slag splash, floating rust and oil stain on the surface of the component, and touch up the damaged or missing part of the primer.
Paint batching and mixing: paint should be prepared as required. When stirring, first pour the paint into the mixer and add water to stir, then add high-strength adhesive and steel anti-sticking agent to make its concentration reach the level of spraying.
Painting:
Before formal spraying, try spraying first, and then operate in a large area after passing the inspection by the fire department and the quality inspection station.
After spraying the first layer, dry 70-80%, and then spray the second layer until the coating thickness meets the requirements.
When spraying, the spray gun should be perpendicular to the component with a distance of 6- 10cm, and the spraying air pressure should be kept at 0.4-0.6Mpa.
Paint requirements
The base course with qualified derusting must be sprayed within 6 hours.
Strictly control the interval of each paint.
The coating must be uniform, without leakage, flowing or wrinkling.
The coating thickness must meet the design requirements.
The adhesion of the coating must be ensured.
The surface should be smooth and bright and the color should be consistent.
Construction environment control (construction is not allowed under the following conditions):
The temperature is below 5 degrees Celsius.
The temperature is higher than 40 degrees Celsius.
The relative temperature is greater than 85%.
Strong wind, rain, fog, condensation.
When the temperature is higher than 30 degrees, dry spraying should be avoided.
Quality inspection
Shot blasting for rust removal: the cleanliness is compared and checked according to ISO 8501-1:1988 standard drawing, and the roughness is measured with a roughness measuring instrument, and the range is controlled at 40-75μm m. ..
Primer coating inspection
According to the Method for Measuring Adhesion of Paint Film (GB 1720-79), the coating should be smooth and uniform, free of bubbles, pinholes and dust. Visual inspection should be used.
Check the thickness, each layer thickness and overall thickness meet the design requirements, and check with a thickness gauge. Inspection shall be carried out according to the Method for Measuring Film Thickness (GB 1764-79).
Adhesive tape should be attached to the coating for adhesion measurement, and the adhesive tape should be compacted. If the paint film at one end of the tape does not fall off, it is qualified, and it shall be inspected according to the Method for Measuring Adhesion of Paint Film (GB 1720-79).
fireproof paint
Full-time quality inspectors use graduated steel needles to spot check the coating thickness.
Tap the stick lightly with a small hammer to check whether there is an empty drum.
Observe whether there are cracks on the coating surface and check the flatness.
Touch-up paint: Touch-up paint or repaint the place with insufficient thickness, uneven thickness and empty drum.
Inspection and acceptance: the supervision engineer will organize inspection and acceptance together with the fire department, the general contractor and the subcontracting construction unit.
Prevention and control measures of painting pollution
After the steel members are installed in place, the colored strips are laid on the working platform, and the colored strip guardrail is set according to the wind direction before spraying.
When preparing coatings, we must master the dosage according to the amount of spraying work each time, and use as much as possible to avoid affecting the environment.
According to the size of the wind, the spraying amount should be controlled accordingly to prevent the surrounding environment from being polluted by the wind.
According to the construction conditions and the temperature at that time, use thinner to adjust the viscosity of the coating to prevent the viscosity from being too thick, which is not conducive to spraying and causing pollution.
When the wind is strong, brush painting or airless atomizing sprayer should be used in hidden areas such as corners and eyelets to control pollution.
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