Problems with batch variation arise when coatings are produced by more than one coating manufacturer, or if one coating manufacturer has to produce multiple batches of a coating to complete a job. Typically, variation between batches is minimal and minor differences can be masked through proper application of the product. Nevertheless, there are several steps architects and contractors can take to minimize potential batch variation problems.
1. Determine the amount of coating required up front. This may enable the manufacturer to produce all the coatings in a single batch, eliminating batch-to-batch variation. If a single-batch approach is impossible, the next best solution is to minimize the number of batches needed.
2. Reduce the number of coating manufacturers and coating applicators. Trying to match batches and standards among different coating manufacturers and coating applicators is extraordinarily difficult. Raw materials vary from one coating manufacturer to another, as do manufacturing processes, colour-measuring standards, and equipment. When possible, specify all coatings from a single coating manufacturer and coating applicator.
3. Try to get all metal painted at the same time. Again, one batch of paint with a single application run—using the same operator in the same operating conditions—is the most efficient way to eliminate variables.
4. Finally, if additional coatings are needed to complete a job, always specify the new order matches the original batch number used. This gives the coating manufacturer and coating applicator a consistent reference to use during the production process.
When coatings are applied to metal, two variables can affect their final appearance. The first is the type of metal used (most commonly steel or aluminum). The second is how the metal was pre-treated. To promote colour consistency across all the substrates used on a particular building, the architect or contractor should make the coating manufacturer(s) aware of all the different metals being coated. This allows the coating manufacturer to match colours across the entire range of substrates for a given project.
The architect or contractor should also verify with the coating manufacturer(s) their product has been engineered for use over the desired substrate(s), and that it is compatible with the pre-treatment method used by the coating applicator.
Coatings are formulated using various base resins and pigments. When coatings are mixed, even subtle differences in colour and metamers (i.e. pigmentation effect that causes the same colour to look different under different light sources) can be exposed. This is why viewing colour samples under actual lighting conditions is vital.
Paint chemistries can also change according to the performance specification required for the coating. The same pigment deposited in a polyvinylidene difluoride (PVDF) coating will usually produce a colour that looks different from the same pigment in an acrylic coating.
For this reason, it is essential architects and contractors communicate to their coating manufacturers all performance specifications related to a project. If more than one performance specification is required, colours must be matched in each resin chemistry before application.