Theoretical Application Amount and Actual Application Amount

• • Theoretical Application Amount and Actual Application Amount

    1. Theoretical Application Amount

    In general, the recommended dry film thickness on the physical properties data sheet is presented based on a simulated ideal flat surface. The amount of application on the data sheet is also the theoretical application amount calculated based on it. The theoretical application amount is an amount that does not consider the surface condition to be coated, coating method, coating environment, and the amount of paint loss during coating. The theoretical application amount can be calculated simply by the following formula.
    
    S (㎡/ℓ) = 10V/Tm
    Here, S: Recommended Application Amount, meaning how many ㎡ can be coated with 1ℓ.
    V: Solid Volume Ratio (%), meaning volume solid.
    Tm: Recommended Dry Film Thickness (μ).
    Example) What is the recommended application amount for a paint with a solid volume ratio of 55% to form a dry film thickness of 50?
    <Explanation>
    10×55/50 = 11.0(㎡/ℓ) The recommended application amount is 11.0㎡/ℓ.

    2. Actual Application Amount

    Despite the manufacturer’s detailed data on the paint, it is very difficult to accurately calculate the amount of paint used in the actual site. Due to various factors in the actual site, more paint than the theoretical paint consumption is used. The difference between the theoretical paint consumption and the actual paint consumption is called loss, and when expressed as a percentage (%) is called loss rate.

    1) Surface Roughness Coefficient

    The amount of paint loss depends on the unevenness of the surface after the surface treatment, and the coefficient according to the unevenness of the surface is shown in the following table.

    Surface Roughness Condition	Primer Coating Coefficient	Intermediate Coating or Top Coating Coefficient
    New smooth steel, picked steel	0.95	0.98
    Blast cleaned steel	0.90	0.95
    Power Tool cleaned	0.85	0.90
    Blasted-lightly pitted steel	0.85	0.90
    Blasted-heavily pitted steel	0.80	0.85
    Rough concrete or Masonry	0.60	0.75

    2) Coating Condition Coefficient

    There are many differences in paint loss according to the coating equipment and other environmental conditions. The coefficient according to this is shown in the following tab

    Coating Conditions	Coefficient for All Coatings
    Brush or Roller	0.90
    Spray-Interior	0.80
    Spray-Exterior*	0.70

    3) Actual Application Amount

    Actual Application Amount
    Actual Application Amount (㎡/ℓ) = Recommended Application Amount (㎡/ℓ) × Surface Roughness Coefficient × Coating Condition Coefficient

    4) Example

    The undercoat with a solid volume ratio of 55% is intended to be coated with a dry film thickness of 50㎛. The surface treatment is blast (henvily pitted steel), the coating equipment is a spray, and the outdoor coating is done in an area without wind.
    Here, What is the actual application amount?
    
    ① Recommended Application Amount = 10×55/50 = 11.0 (㎡/ℓ) ② Actual Application Amount = 11.0 × 0.8 × 0.7 = 6.2 (㎡/ℓ) ③ Loss rate = 11.0-6.2/50 × 100 = 43.6%