Last week on our website we wrote and posted an article about deterioration in delamination of historic Tinner’s Red type paint on standing seam metal roofs and other types of historic metal roofs. This week we will specifically delve further into the topic and discuss the methodologies related to maintenance and upkeep of historic painted terne and standing seam metal roofs. The outline of today’s discussion follows below:
- Caring for Historic Painted Metal Roofs
- Paint Condition Assessment
- Repair Approach Selection
In the next week’s discussion we will touch on the following topics.
- Causes of Paint Distress
- Paint Selection
- Surface Preparation
Caring for Historic Painted Metal Roofs
Last week we explored the issue of red paint delamination on standing seam terne-coated metal roofs, a common concern for a portion of historic DC buildings. A rough ball park estimate is that around 10% of the old historic roofs in DC still have standing seam metal roofs remaining.
This deterioration not only impacts aesthetics but more critically, threatens waterproofing integrity as metal panels are exposed to corrosion. To expand on preserving metal roofs, this article will delve into best practice maintenance and repair methodologies to prolong the service life of painted architectural metals.
Historically, coating vulnerable steel or iron roofing with terne metal alloy provided durable corrosion resistance. The natural patination of terne develops a protective barrier, while oil-based paints further insulate against weathering.
Multiple layers, in one sense, create redundancy should one surface exposed layer deteriorate. However, maintaining paint integrity requires attentive care across decades, and surface wear does not address the concern or issue of substrate layer delamination. We will touch on common causes of coating failures and appropriate rehabilitation approaches.
Conditions Survey
The first step is a condition survey of the upper low-slope roof conditions. Observation of paint cracking, flaking, blistering or delamination signals a distressed condition. However, the extent and severity must be mapped. Supple surface micro-cracking may be monitored, while widespread peeling to bare metal necessitates quick intervention before water infiltration and rust. Gentle probing of suspected deterioration areas can determine if the paint is still adhered. Documentation provides a baseline for tracking changes over time with tape mark-ups and video or photography and measurements areas of concern can be mapped. A condition survey like this should be conducted at least every year, proactive management of specific problems can prolong durability and significantly save costs over the years.
A list of common visually identifiable signs that can indicate problems with paint on historic metal roofs follows:
- Chalking – The binders in the paint deteriorate over time, causing the pigment to turn into a fine powder on the surface. This chalky residue washes away to expose unprotected metal.
- Alligatoring – Advanced stage of paint ageing where the surface develops a cracked pattern resembling alligator skin due to embrittlement. The interconnected cracking provides pathways for water intrusion.
- Wrinkling – Paint film shrinks and wrinkles due to improper adhesion, frequently from applying a hard topcoat over a soft primer or underlying layer. Provides openings for moisture.
- Bubbling – Trapped solvents or moisture under the coating tries to escape, forming bubbles beneath the paint that distort the surface.
- Rust bleeding – Rust formation under paint layers causes discoloration as the corrosion leaches through. Indicates active substrate oxidation.
- Erosion – Paint wear from wind, rain, foot traffic or other mechanical abrasion. Typically the top layer erodes to expose undercoats.
- Peeling/curling – Total paint delamination where the coating has lost adhesion and detaches from the roof substrate, providing no protection.
- Ponding water – Paint flaws allow standing water gathering in low spots instead of shedding, which accelerates deterioration.
In this upcoming week’s article, we will continue on this topic and discuss 1. Causes of Paint Distress, 2. Paint Selection, 3. Surface Preparation.
For effective low slope and mansard roof care in Washington, DC, chose a contractor like Dupont Roofing who has a passion for historical methodologies, waterproofing, and building science. Roofs safeguard both historic and modern buildings, which are significant investments. We urge clients and readers to prioritize quality construction, building upkeep, and consider building a connection with us. Explore our blog for more insights. If you have questions about your Washington, DC building’s roof, reach out through our webform – we’re here to help.
