During the coating process, the consumption of anti-corrosion coatings is influenced by various factors, so their consumption is not fixed and each steel structure project has its own common consumption characteristics. On the other hand, in the anti-corrosion coating of steel structures, paint consumption is inevitable. However, excessive consumption not only requires us to consume more paint, but also directly leads to the addition of engineering costs. At the same time, adding VOC emissions increases environmental pressure. Therefore, controlling the consumption of anti-corrosion coatings within a reasonable range can not only prevent the spoilage of coatings and reduce the overall cost of the project, but also provide a more accurate understanding and understanding of the specific reasons for the consumption of anti-corrosion coatings before construction.

Reasons for coating loss in anti-corrosion coating of steel structures

The loss coefficient of anti-corrosion coatings for steel structures refers to the ratio of practical application amount to theoretical application amount minus 1, usually expressed as a percentage. The formula is: coating loss coefficient=(practical usage amount - theoretical usage amount)/theoretical usage amount. There are various factors that affect the loss of anti-corrosion coatings for steel structures, including additional coating thickness planned and practical coating thickness, surface roughness, steel structure type, coating construction methods and tools, environmental factors at the construction site, skill level of construction workers, and other coating losses.

Planning additional film thickness and practicing coating film thickness

The requirements for planning film thickness are specified in various world or national standards, for example, in ISO 12944:2017 "Protective Coating Systems for Paints and Varnishes - Corrosion Protection of Steel Structures", additional dry film thickness values are specified for planning in different environments. To ensure coating quality, the measurement of film thickness should meet the following requirements:

1. The arithmetic mean of film thickness in all areas to be tested should not be less than the additional thickness of the dry film;

2. The film thickness value of all areas to be tested should not be less than 80% of the additional dry film thickness value;

3. The detection points below the additional thickness of the dry film but equal to or greater than 80% of the additional thickness of the dry film should not exceed 20% of the total detection points;

4. The film thickness value of all areas to be tested should be equal to or lower than the specified maximum dry film thickness value. If there is no regulation, refer to ISO 12944-5.

This is the "Double 80 Principle" in the steel structure coating industry, and there are also higher requirements for the "Double 90 Principle" in some projects. Due to the theoretical application amount being calculated based on additional dry film thickness, in practical painting operations, in order to meet the "Double 80 Principle" or "Double 90 Principle", the overall film thickness will inevitably be sprayed too thick, leading to an increase in practical application amount. In general, the loss coefficient between the planned additional film thickness and the practical coating film thickness is 20%~40%.

Surface roughness

In the anti-corrosion coating of steel structures, sandblasting or shot blasting is generally used for pre-treatment of steel structures. The purpose of doing so is to achieve a substrate treatment of Sa 2.5 or higher to ensure the adhesion and corrosion resistance of the paint film. Due to the different types of abrasives used, the surface roughness of the substrate may also vary.