Ferrous Metal Rooftop Elements and Upkeep – PART IX

In a recent series of articles, we discussed common types of non-roof components found or flat roofs.  Today we start a new group of articles focused on Roofing problems caused by oxidation of ferrous metals. Some of the problems associated with deterioration and oxidation Affairs Metals include delamination and or separation of membrane attachment or roof sealing type materials from the substrate or adjacent metals.  We start by discussing delamination.  

The outline of this series of articles follows:

• • Common types of non-roof components found or flat roofs
    • Access Systems 
    • Historic Brick chimneys
    • Air Exhaust systems
    • HVAC systems
    • Electrical power distribution
    • Low Volt and communication wiring and satellite / antennas
    • PV Panels and mounting structures
    • Guardrails and fall protection systems
  • Roofing problems caused by oxidation of ferrous metals
    • • Delamination
      • Staining and bondability
      • Structural component failure
      • Leakage through metals
  • Methods of Repair and sustainability 
    • • Standard Coatings
      • Substrate preparation
      • Advanced re-coatings
      • Special roofing provisions

The picture below shows a DIY enthusiast working at the arduous task of removing rust from the surface of a mild Steel fire escape. This particular fire escape, like the others access stairs shown in the pictures above, works to give people access away from the building to egress from an emergency situation.  Some building requirements require multiple egress points from a building in the case of an emergency.  Here, in this example, this man has undertaken the onerous job of removing the rust covering the substrate metal.  Several types of alkyd paints can bond well to clean bare metals but only a very few types of chemical converting paints can bond to rusty metals.  Here in this case, where the area to be repainted is so large, it is often best to sand and remove the rust from the metals.

Paints and liquid-applied industrial coatings often fail to bond effectively to rust and iron oxide primarily due to the presence of corrosion and the compromised surface condition. Rust is the result of the oxidation of iron or steel when exposed to moisture and oxygen over time. This process creates a layer of iron oxide, which poses several challenges for adhesion: 

Rust often forms in a flaky, uneven pattern. These surface irregularities create physical barriers, preventing the coating from making direct contact with the underlying metal.  Rust does not offer a suitable substrate for adhesion. Unlike clean metal surfaces, which allow coatings to bond through mechanical and chemical interactions, rust lacks the necessary smoothness and cleanliness. As well, even though steel and iron are considered super high strength, rust is inherently weak and brittle, making it a poor foundation for adhesion. Coatings may adhere initially, but they are more likely to peel, chip, or crack as the rust continues to expand beneath them.  Most coatings, without chemical rust converters, cannot fully halt the corrosion process, as rust can continue to develop underneath the coating, eventually causing detachment and failure. 

To ensure effective bonding and corrosion resistance, it is often necessary to remove rust and treat the metal surface before applying paints or coatings. Surface preparation methods like abrasive blasting, grinding, or chemical treatments are commonly employed to remove rust and create a suitable surface for adhesion in large industrial settings, but often impractical, untenably expensive, or unsafe in smaller applications.  Particularly, because of the risk to other important surfaces, in historic restoration, it is uncommon to use large scale methodologies to prep steel and iron for repainting.

A very similar access stair, leading to a flat roof follows in the picture below. The rungs of this ladder penetrate through a modified bitumen low slope roof membrane and connect to the wood deck substrate below the roof. The modified bitumen membrane is merely welded around the perimeter of the steel ladder rungs. This roof was installed many years ago and in today’s environment of increased diligence and improved quality, an overlay of stronger and more flexible material should be installed to prevent leakage and delamination at the ladder rungs.

The full length of a similar ladder, built on an adjacent property at the same time as the one should in the photo below follows in the next photo this installation is very similar, but at least in the case of the ladder below, the base of the steel bar rungs is wrapped with a base flashing of modified bitumen up a few inches above the roof membrane onto the steel bars.

Smart and proactive replacement, construction, upkeep and maintenance of low slope roof and mansard roof systems requires an enthusiastic interest and understanding of historical methodologies, waterproofing principles, and building science.   Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building. 

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the roof and related systems of your building in Washington DC, contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.