Get the Right DFT for Optimal Coatings Results

June 28, 2021

DFT_test chartGetting the right DFT (dry film thickness) on a coating application is an important part of successful corrosion mitigation. If your DFT is too thin, it may not provide enough protection. If it is too thick, you will waste paint and money. The improper DFT can also alter characteristics such as gloss, dry time, hardness, adhesion, and other physical properties. Each Cortec® Micro-Corrosion Inhibiting Coatings™ product data sheet lists the recommended DFT at which the coating will perform best and should be followed carefully for optimal results.

Unfortunately, painters sometimes run into DFT problems when coating uneven metal profiles. For example, a sandblasted surface may have microscopic peaks and valleys where rust was removed. If the variation in height is 1 mil (25 μm) and the coating DFT is 2 mils (50 μm), the peaks will have less protection than the valleys and become weak points in the coating. To compensate for the surface variation, in this case the painter would need to add 1 mil (25 μm) DFT (the thickness of the uneven profile) on top of the recommended 2 mils (50 μm) DFT for a total of 3 mils (75 μm) DFT.

But how can you know if you have the right dry film thickness when the coating is still wet? The easiest way to tell if the right DFT has been achieved is to measure wet film thickness (WFT) right after the coating has been applied and compare it to the recommended WFT on the product data sheet. Expected DFT can also be calculated by measuring the WFT and multiplying it by the volume of solids to find out what the DFT will be when the coating dries. Conversely, if only the recommended DFT is known, the WFT at which the coating should be applied can be calculated by dividing DFT by the coating’s volume of solids.

Painting thickness checking, Dry film thickness (DFT) inspection for topcoat painting on steel structure in factory.

Take a closer look at our WFT and DFT recommendations by browsing our primers, topcoats, and removable coatings today:

For a PDF version please click here.