*Often there is a lot of confusion when paint consumption is going to be calculated. Various paint **manufacturers arrive at different volumes, and thereby also different costs, when giving quotations **for a specific job. It is not possible to find the true coating costs without a uniform method of **calculating. The following requisites are necessary for calculating the correct quantity and coating **costs: *

*a. Percent volume solids of the products*

*b. Dry film thickness recommended*

*c. Number of coats*

*d. Surface area and condition of area to be coated*

*e. Method of application*

*f. Cost per liter paint*

*g. Loss factor*

*CALCULATIONS OF PAINT CONSUMPTION*

*CALCULATIONS OF PAINT CONSUMPTION*

*Percent Volume Solids (% VS)*

*Percent Volume Solids (% VS)*

*Percent volume solids is the volume percentage of solid material in the coating. The remaining **volume percentage consists of volatile solvents or thinners. The solids are the film-forming portions **of the coating that will remain on the surface after drying or curing. Percent volume solids is the **only true basis for calculating paint volumes required. Solids content quoted by weight is a figure **that for most coatings and applications is meaningless. The percent volume solids is found in the **technical data sheet (TDS), but can also be found or verified by standardized tests.*

*Dry Film Thickness (DFT)*

*Dry Film Thickness (DFT)*

*The dry film thickness (DFT) of an applied coating can be determined if the percent volume solids **(% VS) and the wet film thickness (WFT) are known. This information can be obtained from the **manufacturer’s Technical Data Sheets. The equation for calculating the dry film thickness is:*

*Example 1:*

*A coating is to be applied at wet film thickness of 250 microns, and the volume solid is 50 percent.*

*The equation becomes:*

**Wet film thickness (WFT)**

*The wet film thickness can be determined if the percent volume solids (% VS) and the dry film **thickness (DFT) are known. This information can also be obtained from the manufacturers **Technical Data Sheets. The equation for calculating the WFT is:*

*Example 2:*

*A coating is to be applied at a dry film thickness of 100 microns, and the volume solid is 65%.*

*WFT= 100 microns x 100%/65% = 153.9 microns = 154 microns*

*The coating must be applied in a WFT of 154 microns since 35% of the paint is solvents that will **evaporate.*

*Wet film thickness after thinning*

*If the coating is thinned 20% to adjust the viscosity for application the solid by volume will change, **it decreases. The new volume percent solids can be calculated or found in a table.*

*Example 3:*

*If one liter of a coating with 65% volume solid is thinned 20%, the total volume of the coating will **increase to 1.2 liters. The new percentage by volume of solid is:*

*VS after thinning: % VS prior to thinning / New volume of paint = 65% /1.2 litres= 54%*

*The new WFT, to get a DFT of 100 microns after adding 20%, is: *

*New WFT: 100 microns x 100% /54% = 185 microns*

*The coating must be applied in a WFT of 185 microns, since 46% of the paint in the tin is solvents **that evaporate.*

*Example 4:*

*Another way of calculating the new WFT after thinning is given by the formula:*

*New WFT: DFT x (100 + % added thinner)/% VS = 100 microns x 120/65% = 185 microns*

*See also the table “Volume solids after thinning”.*

*Theoretical spreading rate of a coating*

*Theoretical spreading rate of a coating*

*The theoretical spreading rate (m2 /litre) is the area covered by one litre of paint for a given dry film **thickness. Thus, the spreading rate can be determined if the percent volume solid and the desired **dry film thickness are known. The equation for calculation is:*

*Theoretical spreading rate, m2/litre = % VS x 10/DFT*

*How to arrive at the constant 10 is shown below. *

*8.7 Consumption of paint, theoretical value*

*The theoretical consumption of a coating can be determined if the area (m2), the percent volume *

*solid (% VS) and the desired dry film thickness (DFT) are known. The equation to get the*

*theoretical consumption is:*

*The constant 10 is a correction factor for the different units included in the formula and derives*

*from the following:*

*First, let us calculate the paint consumption in m3. Here we have to include the correlation factor*

*for transforming from meters to microns. We know that 1 m = 1.000.000 microns, and get the*

*following equation:*

*However, we would like to order the paint in liters and not in m3. Then, we have to convert by*

*introducing that 1 m3*

*= 1000 liters, and we get the equation:*

*Paint consumption = Area x DFT / % VS x 10*

*giving the formula as below:*

*Example 5:*

*The outside of a tank is to be painted. The total area is 500 m2. The following paint system is to be*

*applied by airless spray:*

*How much paint do we need theoretically for the job?*

*8.8 Paint consumption with loss*

*The above example assumes that there is no loss of paint during the job and that every drop of paint*

*is applied to the surface. In a real situation some of the paint will be lost:*

* The coating may miss target due to strong wind, very complex geometry of the structure or **by poor application technique. *

* Overspray due to complex geometry of the structure or by poor application technique.*

* Some material will be left in the pump, the tins or in the container.*

* Dead volume *

*Such paint losses are usually in the range of 25-40%, but may accumulate to as high as 50% of the **total theoretical volume. Loss of paint must always be included when the total paint consumption is **calculated. Further, it is important to calculate the volume of paint to order in the correct manner. If*

*the theoretical amount of paint needed is 100 liters and the loss is 40%, only 60% of the actually **paint is left on the surface after painting. The loss factor is 0.6. The equation for calculation is:*

*Example 6:*

*The same figures as for Example 5 are used, but now a loss of 40% (loss factor of 0.6) is included. **The correct amount of print to order will be:*

*Paint consumption with Loss- and Dead Volume factor*

*Paint consumption with Loss- and Dead Volume factor*

*Blast cleaning will increase the surface roughness and thereby increase the surface area. The **roughness will depend on the abrasive used. However, the consequence is that more paint is needed **to cover the increased area. The ‘dead volume’ is the amount of paint needed to fill in for the **roughness (profile) on the blast-cleaned steel (from the bottom to the top of the valley). The amount **of paint (1/m2 ) needed to fill in the roughness is indicated below:*

*NB! The “dead volume” factor only affects the paint consumption for the primer or the first coat of **a paint system.*

*Example 7:*

*Here example 6 is taken one step further. The loss is 40%. The surface of 500 m2 **is blast cleaned to **Sa 2 ^{1/2} with a roughness of 60 microns. A roughness of 60 microns gives a dead volume of 0.04l/m *

*(see table above).*

*The paint consumption with loss, calculated in example 6, is:*

*The total need for Epoxy mastic is: 39 liters + 196 liters = 235 liters. As the dead volume will have **no influence on the topcoat the volume of the Polyurethane is the same as in example 6:*

*Summary of Paint formulas*

*Summary of Paint formulas*