19th December
The UK embraces ‘Outdoor Living
A noticeable escalation in ‘outdoor living’ has occurred over the past few years in the UK, not hitherto known for al fresco dining. On the domestic side, making more of the outdoor expands the ‘usable’ size of one’s home. In hospitality restaurants and pubs are concentrating a lot more on their outdoor facilities, something they got used to doing during the covid pandemic. City and town councils are installing more street furniture and play apparatus.
Metal needs superb protection if it is to withstand the British weather and remain looking smart and being safe for use. The secret to corrosion protection for powder coated metal is five-fold. It starts with good design of the metal component. This must be followed by professional metal pre-treatment, the use of high-quality powders, professional application and finally, a very low maintenance schedule.
All You Need to Know about Metal Protection for Outdoor Furniture and Architecture
Powder coating is a fantastic system to protect metalwork across many applications and in all environments and like any process, having an understanding of the benefits to the designer and consumer will enhance the experience.
What is corrosion?
Corrosion on metal is a natural reaction, caused by the exposure of the bare metal surface to water, oxygen, salts, and pollutants. Not all of these need to be present. Condensation on the surface can also cause corrosion even if the metal isn’t directly exposed to rain.
Rust is a specific type of corrosion formed by the action of water and oxygen on iron or steel. Rust can form underneath paint – the slightest microscopic flaw in the coating allows water and air to reach the metal and rust begins to form, creeping underneath the paint or powder coating. As it does so it expands, forming a mass far greater than the area of steel it is covering and begins to lift the paint, causing bubbling and cracking and blistering which leads to further corrosion.
Common causes of corroded metal
- Inadequate surface preparation before it is coated
- Scratches/damage exposing bare metal
- Pinholes or weak spots in the paint
- An incorrect coating system for the environment. Damp, humid, wet and salty and highly polluted environments all demand different levels of primer and coating.
- Paint peeling. This is often a symptom of corrosion but can also be the cause if it peels off due to inadequate adhesion of the paint or powder coating. It may also peel if it is degraded by UV. A low-grade coating may allow water to permeate and begin to cause corrosion.
The Best Way to Prevent Architectural Metal Corrosion
1. Start with good design
Ideal design features to prevent metal corrosion Powder coating will perform at its best when it is applied to a design that has avoided pitfalls which encourage corrosion.
A good design uses:
- Rounded edges instead of sharp corners. This ensures an even film thickness.
- Drainage holes for hollow sections
- Avoids horizontal ledges where water pools
- Avoids tight crevices that trap moisture
- Uses the same materials where possible to prevent galvanic corrosion
- Avoids steel fasteners on aluminium unless isolated
Read our Design Guide for Architectural Metal
2. Pretreatment: The most important step in corrosion prevention
Good surface preparation is needed even before the pre-treatment process. Any contamination left on the metal creates a weak point where corrosion begins.
De-greasing is necessary to remove oils, fabrication residues, and fingerprints
Mechanical cleaning (blasting) is used on steel to remove mill scale and rust
Powdertech Corby pretreatment systems:-
We use 6-stage chrome-free Titanium-Zirconium pre-treatment for Aluminium and an 8-stage chrome-free silane system for galvanised steel. For mild steel we offer a system of primer coats as a first stage corrosion protection before the top coat.
These processes remove any oxide layer that has formed, chemically prepares (etches) the surface and ensures strong adhesion and corrosion resistance.
The multi-stage pretreatment systems include the etching, conversion coating and a number of de-ionised water rinses between stages.
A good pretreatment can double, or triple, the life of a coating
3. High performances powders for the topcoat
Is a zinc-rich primer needed?
Depending on the environmental conditions (see our C1- C5 Corrosion Chart) a primer may be required before the topcoat is applies, if the environment is marine,
has high humidity or is very polluted. We use zinc-rich epoxy primers. See Primers and Lacquers
Architectural powder coatings
For the outdoor environment, architectural powder coatings from reputable manufacturers will always give the best results. These have been subject to many tests, including those for reaction to fire as well as corrosion and abrasion resistance, and colour durability. Read our description of acetic acid salt spray testing here. There are also many datasheets and test results sheets to be found in Datasheets on our website here.
All our finishes are from leading powder manufacturers. Visit Finishes and Manufacturers
4. Powder application and curing
The applicator must ensure that
- Edges are coated adequately
- The coating is applied to the correct thickness. This is typically the following for outdoor structures:
- Primer: 60–80 microns
- Topcoat: 70–100 microns
- Total system: 130–180 microns
- Corners and welds are fully covered
- There are no pinholes or thin spots
- Curing must be at the exact temperature and for the correct amount of time. `Under-cured powder breaks down early. Over-cured powder becomes brittle.`
- There is uniform heating for large structures like pergolas
- Curing is complete. An under cured coating will have affect adhesion and gloss.
We detail the powder coating process on our website here
5. The importance of installation & aftercare
During installation, best practice advises
- Protect coated surfaces from scratches and other trades.
- Do not drag metal components on the ground
- Avoid cutting/grinding near installed coated items
- Touch up any chips immediately with a compatible paint
Aftercare:
Powder coatings are very low maintenance, but their longevity is improved if the following steps are carried out. A clean surface will corrode far more slowly than a dirty one.
- Rinse every 6-12 months with clean water
- Remove bird droppings, salt, or chemicals which will encourage corrosion.
Paying attention to all of these steps ensures that your powder coated products will be long lasting in their outdoor environments, retaining their structural integrity and looking smart for many years to come.
Contact us to discuss your project. We have worked with many landscape architects and understand the issues that can arise – particularly with product design. Involving your powder coater at this stage will avoid potential costly problems.
