Why Edge Retention In Coatings is Crucial for Durability

Coating durability is intrinsically linked to service life. The more durable a coating is, the longer it will remain in service to provide a greater ROI for owners and operators. It’s also a given that a more durable coating will be less susceptible to wear, and will require less maintenance as a result.

The tricky thing about durability is that it’s not guaranteed. Many factors in the application process and the drying process can impact a coating’s durability (in a negative way, more often than not). And while lab tests may be performed on coatings that have been applied to flat substrates with no features, real world structures are riddled with curves, corners, and intricate geometries that influence a coating’s behavior. That’s to say, a coating that performs well in a controlled lab setting may fail much more quickly than anticipated on an offshore structure– a critical shortcoming of many of today’s standard testing methods.

Coating failures are prone to occur along those features, and it’s not just by coincidence. This brings us to the principle of edge retention in protective coatings.

It’s very common for coating failures to occur at sharp edges, joints, and crevices– but why is that? This pattern can be attributed to poor edge retention.

Edge retention can be defined in a few different ways, but in this context we’re referring to edge retention as the percentage of coating thickness that remains on an edge after application and curing, in comparison to a surrounding flat area. So, for example, if a coating were to be 5 mils thick on an edge but 10 mils thick on the surrounding areas, it would have an edge retention value of 50%.

As a coating dries, surface tension will build. When tension builds on a coating applied to a flat surface, not much happens. On those areas, assuming correct application, the coating will perform just as anticipated. It gets tricky around those geometric features, like edges and corners. In these areas, the increase in surface tension will cause the coating to pull away from the edge, resulting in thinner coverage once the paint has completely set. Drying in such conditions also places that area’s coating under a higher amount of stress compared to flat areas. Where the coating is thin and tense, it’s not going to perform as it’s supposed to. This is in respect to not just impact resistance, but also UV and temperature resistance as well.

Naturally this raises the question of how one can improve edge retention. Doing so can drastically reduce the potential for coating failures at critical points, but this is much easier said than done.

One proposed solution is to grind all sharp edges to a smooth curve. However this is not feasible on all edges and corners, and even when it can be done, the sheer volume of work needed to employ this strategy on an offshore structure makes it a clear dud. A much more common practice comes in the form of stripe coating– but is it really any better?

To quickly define stripe coating, it is the practice of manually applying a preliminary coat to just the edges of a structure. This doesn’t call for any fancy equipment, just a man and a brush. The stripe coat method is by far and away the most common way to try and mitigate poor edge retention. In theory, it makes sense. If the coating wears thin at these known points, just apply more to reach the desired thickness. Easy, right? Well, not quite…

See, stripe coats don’t solve the issue of surface tension increasing as the paint dries. At the end of the day, it’s still the same coating, so it’s going to fail the same way. Although building up another layer seems like it would at least help with the thickness of the coating for better edge retention, doing so can invite more harm than help. Just as certain defects are more prone to occur on thinner coating segments, others can occur in areas with excess coating. These defects can be quite severe, including things like cracking, splitting, or lifting, which leave the substrate alarmingly vulnerable.

Combine this with the fact that stripe coats take just as much time to apply as a full coat, and it’s easy to see that it’s not quite the solution it’s made up to be. Although stripe coating may seem like a viable way to improve edge retention at first, it ultimately creates more trouble than its worth. That’s not to mention the costs associated with applying the stripe coat, the time it takes for it to set enough for the next full coat to be applied, and the resources wasted when it has to be done all over again.

If stripe coating is a waste of resources and building coating thickness around trouble areas can potentially lead to new defects, what’s an operator to do? There is one surefire way to guarantee effective edge retention despite the aforementioned challenges. That is– choose TESLAN®.

TESLAN® is a two-coat system consisting of a primer and a topcoat. These two products have been tested for edge retention independent of one another, and the results simply speak for themselves. When applied to 3 90-degree angle samples of the most common substrates found offshore, TESLAN® primer displayed a perfect, 100% edge retention. And yet, that stellar performance was even outdone by TESLAN® topcoats, which demonstrated 103% edge retention in what may be an industry first.

While an even coating application is certainly pleasing to the eye, the benefits of TESLAN® systems go far beyond aesthetics. This unrivaled level of edge retention places TESLAN® protective coatings in a league of their own, drastically reducing the potential for failures at those common defect sites like sharp edges, joints, and crevices. This is achieved without the need to grind any edges down or even employ any special preparations as it eliminates stripe coating altogether. Simply apply the coating system as directed, and let it work its magic. The result is incredible durability throughout, even on complex geometries, which far exceeds the capabilities of any competing systems.

You could fuss with grinding down edges if you have the time, or applying a stripe coat for poor results… or you could save time, increase durability, and boost ROI with TESLAN®. So, which coating do you want in your specification?