ask coating consultant

Ask A Consultant: Q & A with Bill Corbett

As some of you may know, our website features a section called Ask A Consultant. In this section, users are encouraged to submit questions related to KTA’s service offerings. One of our knowledgeable coating consultants then gives a thorough response to help the user solve their issues.

Recently, we received a list of questions that we found noteworthy. Instead of responding only to the user, we felt it would be beneficial to share the question and answer session with all of KTA University. The 4 questions are bolded, with the answers below. Enjoy!

1) What is the importance of protection from future welding or grinding on completed surfaces?

With the exception of weldable zinc-rich primers (holding primers) you cannot weld through coating materials, so all welding (and grinding) should be performed prior to surface preparation and coating application. Repair of coated areas affected by post-application grinding or welding should be performed per the specifications and coating manufacturer repair instructions.

2) What is preferred method of broadcasting sand on decks to ensure uniform coverage; and when is the correct time to broadcast non-skid media over epoxy on decks?

Always follow the coating manufacturer’s instructions for ensuring the uniform broadcast of aggregate and the time lapse between coating application and non-skid broadcast. It can vary by manufacturer and prevailing environmental conditions.

3) To calibrate DFT (gage) use what two things?

According to ASTM D7091 and SSPC-PA 2, there are three steps that should always occur before taking coating thickness measurements, including calibration, verification of accuracy and adjustment. Calibration is performed by the gage manufacturer or an accredited calibration lab. Annual calibration is recommended by many gage manufacturers.

The gage operator can verify accuracy and adjust. Verify the accuracy of the gage using traceable coated standards, then adjust the gage using certified or measured shims (placed on the prepared, uncoated metal) to compensate for roughness, curvature, metallurgy and other factors.

4) If you add 3 quarts of thinner per 5 quarts of paint for airless sprayer how much greater does WFT need to be to achieve required DFT?

Adding three quarts of thinner to 5 quarts of paint is a dilution factor of 60%. I assume you mean 3 quarts of thinner to 5 gallons of paint, which is a dilution factor of 15%. In order to determine the WFT you will also need to know the volume solids content of the coating materials (from the manufacturer’s product data sheet) and the DFT of the coating. Here is the formula:

WFT =   DFT / (% solids by volume / 100% + % thinner added)

Example: 10 mils DFT; 75% solids by volume; 15% thinner addition

10 mils / (75% / 100% + 15%)

10 mils / (75/115)

10 mils / 65% = 15.4 mils wft

Hopefully this will provide you with some guidance.

Bill Corbett, KTA-Tator, Inc.

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