Large scale outdoor installations require significant investment; in order to be cost effective, each piece of the installation must stand up to long term weathering. Under-performing products can result in massive financial losses, however selecting durable products can prove challenging – especially in regions with extreme weather. Online descriptions aren’t always backed up with rigorous real-world testing, so how can we predict which products will withstand years of wear?
Building for an extreme climate
In order to create a long-lasting installation, it is essential to select a site-appropriate finish. Simply selecting a high quality product isn’t always enough to guarantee long term performance, as it may be designed for a very different or less demanding climate. It pays to consult an expert to determine which coating type and formulation chemistry will best meet aesthetic, function, and service life requirements in a given environment.
The problem of long term wear in extreme site conditions was at the forefront for Reliance Foundry in 2009, when a request came in to supply bollards for an outdoor installation in Arizona. The tribal council of the Pascua Yaqui Indian Reservation needed to install a transportation management system around the Casino del Sol. The project would include dozens of Reliance Foundry R-7572 cast iron bollards, all of which would be required to maintain their appearance and structural integrity over a long service life.
At face value the project doesn’t sound particularly challenging. Most professionally produced bollards will stand up to conventional North American weather – however this installation site came with some unique environmental challenges.
Casino del Sol is located about 15 miles southwest of Tucson, in an area commonly referred to as the Arizona flood plains. The local climate is extreme: between July and September, the region experiences such intense rain that locals refer to it as “monsoon season.” It also has some of the hottest weather in the country, with an average daily high of 101 °F (38 °C) in July.
R-7572 decorative bollards are made from corrosion-resistant ductile iron, however subjecting any metal product to those conditions could threaten structural integrity. The finish would need to completely insulate the metal surface from the elements in order to prevent corrosion, accelerated deterioration, and structural damage.
It was immediately clear that a generic surface finish wouldn’t cut it. A finish needs to be resistant to weather conditions that are normal for the project location – even if that “normal” weather consists of blazing desert sun and annual flooding.
Surface finish selection
When selecting a site-appropriate surface finish, specifiers need to balance initial cost against maintenance and service life requirements. A cheap finish will require more frequent upkeep and have a shorter service life, so a higher quality surface finish is usually less expensive over the long term.
In the harsh climate of Casino del Sol, maintenance and replacement costs for dozens of bollards with an inadequate coating would add up fast. The most cost effective option would be a hyper-durable UV and water resistant finish.
Bollard coatings are usually available in either wet paint or powder coating. Both coating types contain resins, additives, and pigments. The major distinction is that wet paint contains solvents, but powder coating contains none. Because of its natural durability, powder coating is the more popular option among bollard suppliers.
The Arizona flood plains are an unforgiving environment for wet paint. Moisture, sunlight, and heat are each “damage functions” that can lead to the breakdown of resin in painted surfaces. When all three damage functions are combined, the effect is much more severe. In such an environment, even premium paint with a high epoxy resin content would require excessive maintenance.
A powder coating finish was selected for the site because it provides a thicker, more uniform coating with superior corrosion resistance. Powder coating is also much less vulnerable to cracking and peeling than wet paint due to the thermal bonding it undergoes during curing.
Of course, selecting a finish isn’t as simple as wet paint versus powder coat. The various resins used in commercial powder coating – epoxy, hybrid, urethane and polyester – all have relative strengths and weaknesses. Different resins are used depending on the performance criteria.
In order to weather monsoon season, the bollards at Casino del Sol would require a finish with exceptional resistance to moisture, UV exposure, corrosion, and heat. No single resin has optimal resistance to all types of damage – a multi-coat system would be required to effectively protect the bollard’s cast iron surface from all the damage functions common to Tucson.
The bollards were finished with a powder coating system consisting of an epoxy primer and a green semi-gloss polyester top coat.
Iron Bollards after Two Monsoon Seasons
Epoxy coatings have excellent weather, corrosion, chemical, and abrasion resistances, however they have one major weakness: poor chalk resistance. Chalking occurs when UV exposure breaks down the coating surface, causing resin and pigment particles to lose adhesion and form a whitish, chalk-like layer. Over time, chalking erodes the paint layer and decreases surface protection. In Arizona’s blazing summer sunshine, an uncovered epoxy coat would chalk rapidly.
Unlike epoxy coatings, polyester based powder coatings have excellent chalk resistance. Their outstanding adhesion, corrosion resistance, and ability to withstand heavy sun exposure make polyester powder coatings an effective top coat for outdoor applications.
When combined, a powder coated epoxy primer and polyester top coat create a highly durable finish that is able to withstand intense UV radiation, rain, wind, and any other variation of standard weather.
Even with a durable exterior powder coating, monsoon season and flood waters still remained a major concern for the bollards’ long term structural integrity. To address this concern, an additional layer of moisture-resistant epoxy primer was added to the interior of each bollard to prevent damage from long term exposure to standing water.
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After more than 5 years, the bollards are still in service and showing minimal wear. Thanks to site-appropriate design, the bollards have successfully withstood everything the Arizona Flood Plains could throw at them.
The success of Reliance Foundry’s cast iron bollards in a region known for both record temperatures and record rain proves that these durable bollards can perform well in even the most extreme conditions. Architects and specifiers can have confidence that installations with Reliance Foundry products will maintain their appearance and structural integrity for years to come.