The best way to evaluate the cost is on a "unit cost" (cost per square foot per year) basis. To make a proper assessment, consider the cost of surface preparation methods, the cost of materials, and the type of system needed to withstand various corrosive factors of the environment.

The cost of application of any coating system would primarily depend upon productivity.

Although the main element of productivity is that of the applicator (human productivity), there are other factors to consider, viz. equipment cleaning time, physical distribution system efficiency, fatigue time, material preparation requirement and generic system time requirement. As a general rule of thumb, manual roller application is twice as fast as brush application and productivity of spray application (where appropriate) is about three hundred percent that of the manual brush application.

Also, a 3-coat 5-mil (paint film thickness) dry system may last three times as long as a 2-coat 3-mil system. The 3-coat 5-mil system may actually cost less in the long run because it can be maintained by an annual spot painting whereas 3-mil system (thinner paint film) will require complete removal before recoating. In the end, the coating system with low initial cost may be costlier.

Consideration should be primarily given to the expected protective cover requirements.

A simple unit cost formula for 100% utilization at 1-mil paint thickness is : C = P / (16 x S), where C is unit cost per sq ft at 1-mil thickness, P is price per gallon and S is % non-volatile solids by volume.

As can be seen, coating should not be bought on a cost per gallon and square foot coverage basis. Paints low in solids will cover a large area but the paint film will be too thin to give proper protection. Coverage and amounts of materials should always be calculated based on square foot per gallon at recommended mil thickness for proper protection of the surface. Consider the suggested service life of the coating system.

Spot priming should be done before any major rust or corrosion appears. If done regularly, it will cut down significantly on the cost of surface preparation. When more than 10% of the surface requires repairs, it is more economical to repaint properly.