What are the preparatory tasks before painting and the things to pay attention to during painting?

I. Preparations before painting 1. Before painting, it is necessary to check whether all types, models, and specifications of paint meet the requirements specified in the construction technical conditions. Paint that is of substandard quality or has deteriorated cannot be used. 2. Before painting, it is necessary to understand the basic composition and properties of the paint as well as the application methods; appropriate painting tools should be selected based on the specific requirements of each type of paint. 3. Due to the different densities of various components in paint, varying degrees of sedimentation generally occur in paint after storage. Therefore, the paint must be stirred until it is completely uniform before painting. If paint film or particles are detected, filtering should be carried out using an 80–120 mesh sieve. 4. Two-component coatings such as workshop primers and epoxy-asphalt anti-rust paints, available in two separate containers for the component A and component B. It must be mixed evenly according to the specified weight ratio before use; if the mixing ratio is incorrect, it will affect the drying properties and rust resistance. 5. Ordinary paints are already adjusted to a viscosity suitable for application at the time of manufacture, so there is no need to dilute them. However, in conditions of excessively high or low temperatures, an appropriate amount of thinner can also be added to achieve the desired coating viscosity; yet the amount of thinner used should generally not exceed 5% of the weight of the paint itself. II. Precautions for Painting 1. Brushing: When applying paint with a brush, the brushing direction should be from top to bottom first, followed by left to right; the brush should not be dipped in too much paint to avoid dripping. When applying a highly corrosion-resistant coating, the brush should not be held too far away to prevent the paint film from becoming too thin. Special attention should be paid to areas with a rough surface, edges, corners, and protrusions; it is best to apply a preliminary coat first. 2. Roll coating: When using a roller for painting, the paint on the roller should be distributed evenly. During painting, the rolling speed must be kept at a constant level and should not be too fast. Be careful not to apply excessive force when pressing the roller. Special care should be taken with protruding parts such as welds and notches; it is best to apply a preliminary coat first. 3. High-pressure airless spraying: This is the fastest coating method, and it allows for the creation of very thick paint coats. Therefore, to achieve the specified film thickness, it is best to use airless spraying as the application method. When applying the paint in practice, a vertical and horizontal spraying method should be used, either top and bottom first followed by left and right, or left and right first followed by top and bottom. Using airless spraying requires greater skill; the spray gun should be kept at a horizontal distance from the surface to be coated, and care must be taken to avoid moving the spray gun in long distances or in an arc-like motion. 4. Control of paint film thickness: The thickness of each paint film listed in these instructions refers to the thickness achieved through airless high-pressure spraying. To enable heavy-duty anti-corrosion coatings to perform at their best, an adequate paint film thickness is extremely important. Therefore, the thickness of the difficult and stubborn paint film must be strictly controlled. The thickness of each coat applied using a paint brush or roller is relatively thin; therefore, at least twice as many coating passes are required compared to those used in high-pressure airless spraying in order to achieve the desired thickness. During construction, painting should be carried out according to the required amount; a paint film thickness gauge should be used frequently to measure the thickness of the wet paint film, in order to control the thickness of the dry paint film and ensure uniform coating thickness. Determine the density and distribution of thickness measurement points based on the size of the object to be coated, and then measure the thickness of the dry paint film. Areas where the paint film thickness does not meet the requirements must be repainted. 5. The intervals between different types of coatings vary; during application, each type of coating should be applied according to its own requirements. It should be particularly emphasized that for epoxy asphalt thick-coat anti-rust paint and yellow sheep topcoat, the interval between applications must not exceed the maximum interval specified in the instructions; otherwise, it will affect the adhesion between the different layers of the paint film, leading to its peeling off.