Steel Deck Corrosion: Why It Happens, And What You Can Do To Protect Your Investment

steel deck on a commercial building in Toronto

Fluted steel deck substrate is one of the most popular flat roof substrate systems on one storey industrial, commercial and office buildings, and with good reason.

It is relatively quick to install in most weather conditions, durable and cost-efficient relative to alternatives such as wood, concrete, precast concrete, core slab or tectum.  It has been in the market for over 60 years.  Metal deck substrate has been known to have a lifespan of over 40 years and requires minor maintenance to keep it in shape. Steel decks in Canada have performed particularly well under all insulation boards because of the zinc alloy coating and extensive use of vapour retarders.
Roof deck substrate is not intended to be part of the waterproofing of the building envelope, but it acts as structural support and can protect against wind uplift when properly secured. Membrane layer(s) and insulation are always supported by a structural roof deck.
However, if a steel deck substrate is not taken care of properly, you can run into some major (and expensive) maintenance problems. Often undetected by property owners, managers, and tenants, deck and mechanical fastener corrosion weaken the roof deck to the point that it can, in some cases, present safety concerns for rooftop equipment and workers.
Here’s what you need to know about steel deck substrates.
steel deck corrosion

Why Steel Deck Corrosion Happens

Steel deck corrosion is affected by three main variables – liquid moisture, oxygen, and temperature. Steel deck corrosion is a result of prolonged exposure to a combination of these, most often leaks that were not remedied for a long period of time and then made worse by exposure to the elements.
If the structure in question was built before the year 2000, it’s also possible that a chemical reaction between moisture and the insulation of the roof is contributing to corrosive damage. Some types of roofing insulation, including phenolic foam and cane-based (bagasse) fiberboard products, that were used in the 1980s and 1990s were highly corrosive in the presence of moisture and where there was no separation layer between the insulation and the top of the metal deck. Corrosion has been found under all types of insulation following long term membrane leakage.  If this is the case, you may need to replace the roof, deck overlay and insulation layer(s) [as applicable], as well as repair and/or replace some or all of the steel deck substrate to arrest structural issues.
If the process conducted within the building in question is highly acidic (vapours from within the building being the most common issue caused by things such as metal plating and acid baths), it could be extremely damaging for your steel deck. If your building is processing items that produce acidic vapour, it’s crucial to have regular maintenance for your roof to ensure damage is not being done.  There is a concern that some deck corrosion on the top side of the deck substrate is hidden from view within the roof assembly and most often the extent of damage to deck substrate is not known until the roof is being replaced and the deck is open for examination once the existing roof is removed.

Where To Look For Steel Deck Corrosion

Steel elements of your deck are in the insulation, so most often deck corrosion issues are found while dealing with leak issues. However, if you are aware that there is a steel deck beneath insulation and you are noticing leaks or ponding issues, there’s a good chance that your steel deck has been affected.
Material testing can determine if damage to deck substrate is a coating or a form of corrosion.
steel deck corrosion

Steek Deck Corrosion Remediation

Steel deck corrosion, like all other roofing issues, can vary in intensity. There are several paths that might used to deal with these issues, as follows:

1. Sometimes the approach is to do nothing at the current time and to continue to monitor the situation to ensure it doesn’t get worse.
2. If the corrosion is minimal or localized, your roofing team may recommend scraping off loose corrosive materials, cleaning galvanized metal surfaces to remove any oil or contaminants – if any, and coating the corroded deck substrate at the affected areas with an approved primer provided that the issue is not structural in nature.
3. Unfortunately, sometimes the corrosion is so bad that it could affect the integrity of your roofing system and safety of roof top equipment and workers if kept, and in these cases replacement of the steel deck, in whole or in part, is often needed.
Click here to view our full list of repair and replacement services.

Preventing Further Damage After Repairs

One of the best ways to prevent corrosion for your steel deck is to have it coated with a rust-inhibiting primer or zinc coating. The coating protects the steel by oxidizing instead of the steel itself, protecting the actual deck from corrosion. Polymeric coating is also an option for steel deck protection, as it keeps moisture locked out of the surfaces.

How This Problem Is Minimized In Our Current Environment

One of the ways that corrosion is prevented today is through factory applied rust-inhibiting primer or zinc coating onto the deck substrate. The coating protects the steel by oxidizing instead of the steel itself, protecting the actual deck from corrosion.  In most of today’s roof assemblies, the inclusion of a vapour retardant separation between the top of the deck substrate and the roof insulation will also inhibit deck corrosion.

What To Do If You Suspect Steel Deck Corrosion

If you suspect that your steel deck is damaged, get in touch with a diagnostic team to assess your situation as soon as possible. As we mentioned above, there are certain types of steel deck corrosion damages that can either be arrested or completely reversed. If you are experiencing leaks on your roof, or are concerned about the integrity of your roof, contact us here. With over 60 years of roofing experience, we have the most qualified team in the GTA to answer and all of your questions. Get in touch today, and get the Elite Advantage.