Check It While It's Wet

The Wet Edge, No. 001. Short field notes for coating crews.

By the time the inspector's DFT gauge touches that steel, the coat you just put on is cured in place. If it's low, you're adding a coat. If it's high, you might be grinding it back off.

The wet film gauge is the one reading that lets you fix this coat while it's still going on. Press the notch gauge square into the fresh film, read the highest tooth that picks up paint, and adjust on the next pass. ASTM D4414 covers the method, and it takes about five seconds.

The math is short: wet film equals dry film divided by volume solids. A 5-mil DFT spec with a 67%-solids epoxy needs about 7.5 mils wet. Thin it 10% and that climbs to about 8.2, because the thinner evaporates and adds nothing to your dry film. Volume solids is on the product data sheet.

Here's why it pays. Low DFT means a punch list and an extra coat, with the masking, the lift and a recoat window to chase. High DFT can mean solvent entrapment, cracking or sags on the verticals. Either way, it's your crew back on the job for free.

Put a wet film gauge in every sprayer's pocket and tape the target number to the pot. It's the cheapest QC tool on the truck.

Bottom line

DFT tells you what happened. WFT lets you decide what happens. Check it wet, while a fix costs one pass instead of a return trip.

Further reading: ASTM D4414, Measurement of Wet Film Thickness by Notch Gages. Standards: ASTM D4414.

Talk to a consultant. Questions on a job? Atlantic Coating Consultants supports contractors in PA, NJ, DE, MD, DC, WV and OH with product recommendations, field support and crew training. Call 484-644-5303 or email atlantic@tnemec.com.