Do you ever have questions about good surface prep and coating adhesion when working with direct-to-metal coatings? Cortec’s Technical Service Manager, Rick Shannon, recently shed light on some frequently asked questions (FAQs) that come up when talking with Cortec® Coatings users.
1. Do I Need to Remove Cortec® VpCI®-41x Series Cleaners Before Coating?
If a sandblasted metal surface is going to sit exposed at least 24 hours before painting, it should be cleaned with a VpCI®-41x Series cleaner to remove grit and grime and inhibit flash rust. Since cleaners such as VpCI®– 414 and VpCI®-416 contain flash rust inhibitors that temporarily adsorb on the metal surface, the question arises of whether the cleaner itself needs to be rinsed off, as well, to ensure good coating adhesion.
The answer depends on how the cleaner was applied and how it has dried. Typically, Rick would recommend rinsing off the VpCI®-41x Series cleaner before painting, especially in areas where the wash water has pooled. However, if the VpCI® cleaner was applied by power-washing and has dried completely without pooling, adhesion should not be an issue, and the VpCI®-41x Series may not need to be rinsed off at all.
2. How Soon Can I Apply a Second Coating of CorrVerter®?
Another common question concerns recoat time. This is important because not waiting long enough for each coat of paint to dry before applying the next one can have a serious impact on adhesion.
In the case of CorrVerter® Rust Converting Primer, Cortec® recommends applying a second coat only after the first is dry to touch. Practically speaking, this often balances out to at least six to eight hours depending on the location and time of year. For instance, in the middle of July in the Northern Hemisphere, CorrVerter® may be ready to recoat in just three hours because the heat dries it out so quickly. But in late autumn as the temperatures fall, it may be necessary to wait overnight to get a full cure.
For any water-based coating, cooler temperatures greatly extend the recommended recoat time because water evaporation rates slow down. In fact, a cool, humid day could double recoat time. If painters have any question of whether a coating is ready to recoat, Rick recommends waiting overnight before applying the second coat. If for some reason it is not possible to wait, he suggests doing a coating adhesion test or solvent rub to see if the coating has cured.
3. How Long Can I Wait to Recoat?
On the other end of the spectrum is the issue of how long is too long to wait before recoating. Rick shared that for some Cortec® Coatings, recoating can wait indefinitely. Coatings such as EcoShield® VpCI®-386 or CorrVerter® can be recoated even a year later as long as the surface is clean. Other Cortec® Coatings, such as VpCI®-395 and VpCI®-396, cannot wait too long before recoating because their resins get much harder. If more than 72 hours have passed since applying these two coatings, the painter will need to scuff the surface before recoating to improve adhesion.
How to Make Use of FAQs
Many variables enter into the equation for each FAQ, and the answers are not always exactly the same. However, they provide a general rule of thumb on how to work with surface prep and coating dry time. The best way to make use of these FAQs is to use a healthy dose of common sense to apply the advice to each unique case. If uncertainty about a particular application still lingers, you can always contact Cortec® Technical Services for further help. Perhaps your own inquiry will even make it on a future list of FAQs!
Keywords: Coating FAQs, Cortec Coatings, coating adhesion, good surface prep, rust converting primer, how soon can I apply a second coating, how long can I wait to recoat, coating adhesion test, solvent rub test, Cortec
For a PDF version please click here.