Painting Contractors:
Two Batches of Paint are Never the Same

A twenty-year-old apartment complex in south Florida was recently repainted. Eight 2 and 3 story buildings were pressure-cleaned, primed, and painted with an acrylic latex, flat house paint. Several months after completion of the project, it was apparent that painted walls were a non-uniform color.

Microscopic examination of the surface of the discolored paint indicated that the discoloration was not due to the presence of efflorescence or surface contamination. ASTM chalk tests revealed that both the discolored and non-discolored areas had only a slight chalk, therefore the discoloration was not due to chalking resulting from a breakdown of the paint resin.

The finish paint had been applied by spraying. A visual inspection of the project revealed that the discolored areas correspond to locations that were adjacent to non-painted surfaces would have been "cut in" by brush. The discoloration problem was caused by the purchase of more than one batch of paint. One large batch was tinted at the factory and used to spray the buildings. Additional paint was needed, and another smaller order was placed. On this occasion, the paint was store-tinted using different colorants. This paint was used to 'cut in' all buildings. The colorants used in the second batch of paint were unstable and faded after a relatively short period of time, resulting in the blotchy appearance observed.

This problem could have been minimized if the painting contractor had retained paint from the original batch to cut in the buildings sprayed with that material.

Coatings ConsultantsText and pictures courtesy of Robert L. Cusumano,
Coatings Consultants Inc.