Why Mils Matter: How to Double Your Impact Resistance

What Is a Mil?

A mil is a unit of measurement equal to one-thousandth of an inch (0.001”), used to measure the thickness of coatings after they dry (Dry Film Thickness, or DFT).

For reference:

• 1 mil = 0.001 inches

• A sheet of paper is about 3–4 mils thick.

Avoiding Confusion Between Mils and Millimeters

It’s important to address the difference between mils and millimeters:

• 1 mil = 0.001 inches

• 1 millimeter = 0.0394 inches

•          

A millimeter is 39.4 times thicker than a mil! Proper communication ensures everyone understands the correct DFT for durability and impact resistance.

Why Counting Coats Doesn’t Work

Many Refinishers think in terms of “coats” instead of mil thickness. Here’s why this approach can be problematic:

• Spraying 3 coats at 1 mil per coat achieves only 3 mils of DFT.

• To achieve good impact resistance, you need at least 6–8 mils of DFT.

Tip: Focus on achieving the right DFT, not just the number of coats.

Solid Content and DFT

The solid content of a coating determines how much remains after solvents evaporate. For example:

• 82% solids coating: Leaves 82% of applied thickness as DFT.

• 60% solids coating: Leaves only 60% of applied thickness.

  Impact Resistance vs. Cost Per Tub

Scenario	Part A Used	Tubs per Gallon	Cost Per Tub	DFT Achieved
Supplier’s Recommendation	12 oz	~10–12	$12.50	~3–4 mils
Proper Application	16 oz	~8	$16.00	~6–8 mils

For an extra $3.50 per tub, you double the impact resistance, ensuring long-term durability.

How to Upgrade Impact Resistance

Stop Counting Coats: Focus on achieving the right DFT (6–8 mils or more).

1. Use High-Solids Coatings: Products with 70–85% solids provide better durability.

2. Upgrade Your Equipment: Invest in a 5- or 6-stage turbine HVLP sprayer.

3. Educate Yourself: Understand the relationship between wet film thickness (WFT), DFT, and solid content.

Don’t Fall for the “Tubs Per Gallon” Game

Suppliers have been playing the “tubs per gallon” game for years, convincing refinishers to stretch their coatings at the expense of quality. By focusing on proper mil thickness, you can deliver a superior product that withstands wear, tear, and impact over time.

Why Primers Matter

 A very simple and inexpensive way to significantly improve impact resistance is by incorporating a primer into your process. I know adding a step may seem like more work but let me give you an analogy that might make it worth considering.

Think about commercial carpet installations.

Often, you’ll see carpets glued directly to the floor. This method is quick and functional, but there’s a trade-off— drop a glass or bottle on that surface, and it’s likely to break on impact. Why? Because the lack of cushioning means there’s nothing to absorb the force of the drop. Now imagine the same scenario with a good carpet and padding underneath.

That same bottle or glass is far more likely to bounce instead of shattering. The padding absorbs the impact, protecting the item. Primers in refinishing work the same way. They create a durable base layer that absorbs impact and provides a better foundation for the topcoat.

How to Compensate for Lost Mils

The minimal mix recommendation by suppliers was likely based on the assumption that a Spray on primer was being used. But in today’s refinishing world, many have shifted to direct-to-surface method by using coupling agents or adhesion promoters. While these methods can work well, they often fail to compensate for the lost mil thickness that a primer would provide. The result?

Topcoats applied without enough build behave more like a glue-down carpet—functional but less forgiving when subjected to impact. There’s absolutely nothing wrong with the direct-to-surface method, as long as you apply enough mil thickness to ensure durability.

However, by reintroducing a primer, you can achieve a higher level of impact resistance and overall quality with minimal additional cost or effort. Or, if taking that extra step is too inconvenient, simply spray down the extra mils of your topcoat to compensate for the lost mils using coupling agents with the direct to surface method.

 

Key Takeaways

• Understand Mil Thickness: Always measure and aim for the right mil thickness (6–8 mils) to ensure impact resistance and durability.

• Avoid Miscommunication: Clarify the difference between mils and millimeters to avoid costly mistakes.

• Use High-Solids Coatings: Opt for coatings with high solid content to achieve better durability and efficiency.

• Invest in Equipment: Upgrade to proper HVLP sprayers for optimal application and atomization.

• Consider Primers: A primer provides a strong foundation for your topcoat, enhancing impact resistance.

Delivering quality results starts with the right tools, techniques, and knowledge. Focus on these principles to elevate your refinishing work and satisfaction.

In refinishing, quality beats quantity every time. A little extra material cost goes a long way in ensuring impact resistance, durability, and customer satisfaction.

By applying more mils and upgrading your equipment, you’re not just improving your results—you’re elevating your entire business.

Remember: It’s not how many tubs you can get out of a gallon. It’s how much quality you can deliver with each tub.

Insights by:

Gary A. Goel, Industry Expert and Founder of Shark Grip Coatings"

Have questions?

Call or Text Me my cell phone 210.475.2199

EAH Industrial for expert advice and premium products."

"Stay ahead of the industry—explore more resources at EAH INDUSTRIAL

Related Products