In life and in business, it’s always nice to know that you have options. As a chemical agent resistant coating (CARC) applicator, you should already know that two exterior topcoats are available, both of which are fully supported by the Army: MIL-DTL-53039 and MIL-DTL-64159. Unless you are contractually obligated to use one over the other, the choice is yours to make. So how can you determine which topcoat system best fits your needs?
Comparing the Two SystemsMIL-DTL-53039 is a single-component, solventborne, moisture-cure urethane. Currently, Type I coatings have a maximum of 3.5 lb volatile organic compound (VOC) content and use silica-based flattening agents. Type II coatings allow for a maximum of 1.5 lb VOC, are volatile organic hazardous air pollutants (VOHAPS) free, and use silica or polymeric flattening agents. With proper handling and setup, these coatings can have an indefinite pot life. Although the Type II coatings have just recently been added to the specification, they have been used widely for several years under the Experimental Products Program (EPP). Official Qualified Products List (QPL) numbers are due to be issued in the first quarter of ’07.
MIL-DTL-64159 is a 1.8 lb VOC/HAPs-free, three-component, water-dispersible urethane system. These coatings are supplied as kits with a 2:1:½ ratios (the ½ being deionized water). They require special mixing instructions and come with a four-hour pot life. Like 53039, 64159 has two types. Type I uses silica-based flattening agents, and Type II uses polymeric flattening agents. Both types are listed on the QPL.
In either system, the Type II, lower-VOC products that contain polymeric beaded technology are considered to be the high-performance topcoats. (Type II beaded is the preferred choice by the Army for various reasons.) Finishing professionals who have experience with CARC are probably fully aware of some of the physical deficiencies of the Type I systems. Because of the silica flattening agents, Type I coatings have poor resistance to scuff, mar, and as some people say, “its color fades in the moonlight.” Conversely, the Type II systems that use the beaded technology exhibit superior resistance to scuff, mar and impact, and they have excellent flexibility, color and gloss retention. Furthermore, these coatings also bring additional corrosion resistance to the CARC system that is absent in both Type I systems.
Choosing the Right TopcoatSo which system and type is best for you and your customer? Here are some points to consider:
- Check your budget. As with any high-performance coating, expect to pay a premium for Type II products, regardless of whether the system is water- or solvent-based.
- Evaluate your quality. If you have excessive paint defects that are a result of handling or processing, the superior physical properties of the Type II beaded technology might minimize related rework.
- Review your production requirements. If the name of the game in your shop is high throughput and efficiency, plan on using the MIL-DTL-53039 solventborne system. The MIL-DTL-64159 material is a water-dispersible system that requires extended flash-off and air dry times, and therefore more processing time.
- Understand individual environmental restrictions, and review your permits to ensure you are in compliance. If your permits allow for 3.5 lb VOC products, does it make sense to switch to a more expensive, more environmentally friendly product?
- Understand your contracts and customer requirements. Do they call for a specific coating, or is it up to your discretion?