Common DFT ranges by system
These ranges describe typical per-coat territory for common generic system types, so you can spot an outlier at a glance. They are orientation figures, not acceptance criteria.
The product data sheet for the exact product and the project specification always govern. Real products vary widely, and both a minimum and a maximum matter: too thin risks premature failure, too thick risks solvent entrapment, mudcracking in zinc-rich primers, and cure problems.
| System type | Per coat (mils) | Per coat (µm) | Note |
|---|---|---|---|
| Inorganic or organic zinc-rich primer | 2 to 4 | 50 to 100 | Excess zinc thickness commonly causes mudcracking - the maximum matters as much as the minimum. |
| Epoxy primer or intermediate | 3 to 6 | 75 to 150 | Wide product-to-product variation; verify the data sheet. |
| High-build epoxy | 5 to 10 | 125 to 250 | Often applied in one or two coats in tank and marine work. |
| Polyurethane finish coat | 2 to 4 | 50 to 100 | Appearance coats; thickness above the data sheet range can affect gloss and cure. |
| Acrylic waterborne topcoat | 1.5 to 3 | 40 to 75 | Thin-film products; verify recoat windows. |
| Coal tar epoxy | 8 to 16 | 200 to 400 | Heavy-duty immersion service; check substrate temperature limits. |
Frequently asked questions
Is more coating thickness always better?
No. Above the data sheet maximum, coatings can trap solvent, crack, sag, or cure improperly. Zinc-rich primers in particular are known for mudcracking at excess thickness. The maximum in the specification is an acceptance limit, not a suggestion.
How do these ranges relate to a specification?
A project specification states an exact minimum and maximum for each coat of the named product. These generic ranges only help you recognize when a specified value or a measured result is unusual enough to double-check.
How do I convert mils to microns?
Multiply by 25.4. So 2 mils is 50.8 microns and 5 mils is 127 microns. CoatSpec's unit toggle does this everywhere in the tool.