Bike Parking Rack Material Selection
The Case for Stainless Steel VS Powder Coated Mild Steel
I don’t know why anyone would buy anything but a bead blasted stainless steel bike rack for an outdoor application. If the goal is to make the bike parking rack look good for the life of the building it’s next to, this is by far the best choice, regardless of where it’s installed. The mild steel rack in the photo below is about 5 years old, installed in a marine environment.
Powder coated racks look great out of the box, and maybe even look OK after some years. Over time and with use, however, the powder coating will show dings, cuts, and abrasions from pedal strikes, heavy locks, and whatever else bangs into it. The rack below shows some of that kind of abuse (the final abusive act being a thief using a pipe cutter to steal the bike that was locked to it).
If the powder coating is breached down to bare mild steel, the rust reaction can propagate beneath the coating fairly quickly.
Stainless steel, on the other hand, has corrosion resistance built into it, as the chromium oxide layer that forms on stainless steel alloys does a very good job of preventing red rust in most common applications.
I say ‘most common applications’, because stainless steel is not perfect. Give me a few hours and a spray bottle of the right acid, and I’ll show you how stainless steel can show orange rust. That said:
- The red rust corrosion on stainless steel rarely goes deep into the metal (this is sometimes referred to as “pitting rust”). Most red rust on stainless steels is a surface condition only.
- Even though it’s a rarity, this red rust corrosion is correctable! Bar Keeper’s friend, Citrisurf, and Naval Jelly are all great products that can make a bead blasted stainless steel rack look like new (see below).
To make a powder coated rack look like new is next to impossible, unless you are willing to remove the rack, get it sandblasted, recoat it, and reinstall it. I’d think that would take a minimum of one week, even if you call in a bunch of favors – probably longer if you don’t work with a powder coater regularly. It pains me to see powdercoated racks embedded into concrete, as that's even worse. Removal of those racks involves running a jackhammer, and reinstallation involves a concrete contractor. The only other option is to rework the racks in situ with a wet paint color match, and hope for the best.
Here is a before and after shot of a stainless steel bike rack that did show some rust over time (with the help of my friend muriatic acid, and Seattle’s famously awful weather), which I then cleaned with a product called Citrisurf. It passivates the surface of the stainless steel, and removes surface oxidation, including rust.
The rack above should look great for years before a cleaning needs to be done again, longer if the environment is not very corrosive.
The downside to stainless steel bike racks is that one color – matte gray – fits all. It’s an “industrial” look, but there are stainless steel racks out there that still have great eye appeal. Sign plates that are integrated into the rack design can help.
And why bead blasted surface treatment over, say, a grained or polished finish? One reason is that if you do have to resort to the cleaning method described above, you can use mildly abrasive pads (I used Scotch Brite for the photo above) without showing scratches in the areas where you worked after you’re done.
If you do require a grained or polished finish, make sure that your rack gets a good passivation step – this removes surface iron that can react to form red rust, and increases the likelihood you won’t have to do a cleaning step at some point in the future.
Resist the temptation to powder coat stainless steel racks. Reason: stainless steel does not react well (or at all) with the common pretreatment chemicals found in most powder coating facilities, which means that the adhesion between the powder coat and the stainless steel substrate won’t be quite as good as it is on a substrate that does react with the pretreatment chemicals. You won’t have a corrosion problem when the powder coating gets breached down to bare metal, but you will still have a cosmetic issue (chipped or scratched powder coating) that’s hard to fix.
If you must powder coat your bike racks for arguably good reasons (like company colors being incorporated into your landscape architecture), use surface mounted racks only. These are much easier to rework or replace when/if the powder coating begins to look tired and well-used. In these cases, it’s a great idea to use a powder coat primer before the colored top coat is applied. High gloss powder coats should be avoided – those will show abrasions and scratches more than a semi-gloss powder would.