Viscosity Check During Paint Application – A Lesson Learned
During a recent steel structure painting project, the coating team noticed that the applied paint was showing excessive sagging and runs on vertical surfaces. The spray equipment was working properly, and the surface preparation met the specification requirements, so the team initially suspected an application issue.
A viscosity check was carried out using a Ford Cup before the next batch was applied. The reading was found to be lower than the value recommended in the paint manufacturer's technical data sheet. Further investigation revealed that extra thinner had been added to improve sprayability without rechecking the viscosity.
Another factor was the ambient temperature. The paint had been stored in a warm area, and the higher temperature reduced the viscosity further. As a result, the coating became too thin and flowed excessively after application, causing sagging and uneven film thickness.
The batch was adjusted to the correct viscosity range, and temperature was monitored before testing. After the correction, the paint application improved significantly, with better flow, appearance, and film build.
This incident highlighted the importance of verifying viscosity before application and understanding how temperature can influence measurement results. Even a small deviation from the recommended viscosity can lead to coating defects and rework.
Discussion Questions
- Have you observed coating defects caused by incorrect viscosity adjustment? What were the findings?
- In your experience, how significant is temperature control during viscosity measurement?