Murals and fine artwork enrich our built environments with beauty, culture, and history. Whether in a cathedral, a historic theatre, or a public building, these artistic expressions require special care to remain intact for future generations. One of the most invasive threats to decorative artwork, especially murals on plaster and canvas, is the presence of moisture, leading to the growth of mold and mildew.
At John Canning & Co., we’ve seen firsthand how moisture damage can compromise both the structure and the aesthetic value of historic artwork. Fortunately, there are proactive steps that can be taken to reduce the risk and ways to preserve the artwork if it’s already been damaged by mold or mildew. Below, we will explore the risks of mold and mildew, measures you can take to prevent them, and what to do if you catch mold invading your artwork or mural.
Understand the Risks: Why Mold and Mildew Form
Mold and mildew are both types of fungi that thrive in damp, poorly ventilated environments, and it’s extremely important to be hyper aware of this during the more humid days of the year. The combination of warmth and moisture in the air creates an ideal breeding ground for fungi.
Presence of mold and mildew on the historic murals at the Luzerne County Courthouse
Mildew typically grows on the surface of damp, organic materials like fabric, paper, leather, and walls and appears as a thin, powdery or fluffy growth, often white, gray, or yellow, and has a musty odor. Mold tends to be black, green, blue, or even red, and is often fuzzy or slimy in texture. Mildew is typically less invasive than mold and grows on the surface of materials, while mold penetrates deeper. Which makes mildew easier to clean as it’s mostly a surface-level issue, whereas mold can cause significant structural damage, staining, and deterioration, especially in buildings and artworks, and is significantly harder to remove. Both can appear on surfaces like walls, ceilings, and artwork when moisture is present, making it very harmful not only for causing structural damage but also posing a health risk, including respiratory issues, allergies, and irritation.
Moisture can enter a historic building in several ways, creating conditions for these fungi to grow. Common sources include roof leaks, cracked or deteriorated masonry, and damaged gutters or downspouts that allow water to seep into walls and foundations. Poor ventilation and outdated HVAC systems can also lead to trapped humidity inside the building. Over time, these issues create a humid environment where mold and mildew can thrive, especially if not promptly addressed. Once the fungi take hold, they not only create unsightly blemishes but can also deteriorate paint layers, weaken plaster substrates, and even lead to irreversible staining.
Examples of paint damage in the Luzerne County Courthouse.
Mold and mildew can cause a range of paint damage to historic artwork and murals, including discoloration and staining, loss of paint adhesion, cracking, peeling, and flaking of paint layers, weakening of the canvas or paper support, and ultimately, the potential for irreversible damage and loss of the artwork. Artworks are especially vulnerable in spaces that were not originally designed with modern environmental controls, making prevention strategies all the more critical.
Key Prevention Strategies
1) Control Humidity and Temperature
The most effective way to prevent mold is by maintaining stable environmental conditions. Ideally, relative humidity should be kept between 40-60% with a stable temperature in the range 65-70°F with minimal fluctuations, since that can be just as damaging as extreme humidity and temperature levels, so always aim for gradual changes. Depending on the artwork’s materials, condition, and history, the range can differ. It’s always best to receive an evaluation from a conservator to establish the appropriate environmental conditions for specific pieces.
A well-calibrated HVAC system is essential. In historic buildings, this often requires integrating modern systems in a way that is sympathetic to the architecture and does not disturb the original historic materials. Regular maintenance and monitoring of HVAC units are vital for keeping the environment stable year-round.
2) Improve Ventilation
Good air circulation prevents the stagnant conditions that mold and mildew require to thrive. This is particularly important in buildings with heavy masonry walls, basements, or areas where air movement is naturally limited. Consider using mechanical ventilation, such as dehumidifiers or fans, in spaces prone to dampness. For structures without central air systems, portable solutions may be a short-term fix, but long-term plans should prioritize integrated solutions tailored to the building’s unique construction and materials.
3) Water Intrusion
Routine inspections of roofs, ceilings, gutters, and exterior masonry are essential. Water ingress from a leaking roof or a poorly sealed window can introduce moisture into the walls and ceilings, putting nearby murals at risk. Even decorative surfaces that appear stable may be hiding moisture behind their substrate. Methods such as using non-invasive moisture meters can help detect hidden issues without damaging artwork.
4) Monitor and Maintain
Once preventative measures are in place, ongoing monitoring is key. You can install humidity and temperature sensors in vulnerable areas, especially attics, basements, or behind walls with murals. Along with using data loggers, which can provide long-term insights that help building stewards identify patterns and respond to any infiltration before significant damage occurs. Historic buildings with any fine artwork or murals should have routine maintenance checks with a visual inspection of the artwork and surrounding walls. Artworks should also be continuously monitored for telltale signs of mold or mildew, such as discoloration, musty odors, or flaking paint, all of which may indicate an early mold issue.
What to Do if Mold Appears
If you suspect mold or mildew on your historic mural or fine artwork, it’s crucial not to attempt cleaning it yourself, especially without a professional assessment. Some molds are at high risk of health concerns, and performing typical cleaning acts such as using vinegar, bleach, or even certain soaps can permanently alter paint pigments and cause even more damage.
Our conservators at John Canning & Co. are trained to assess, contain, and reverse damage in ways that protect both the artwork and the people interacting with it. Early intervention is essential; the longer mold is present, the more likely it is to penetrate through paint layers or weaken plaster substrates.
Luzerne County Courthouse mural after conservation. Photo Credit © Robert Benson
Mold and mildew may be invasive, but the fight against them is possible with experienced conservation practices, thoughtful environmental control, and a deep respect for the materials and stories these artworks embody.
We’re committed to helping historic buildings safeguard their artistic and architectural heritage. Whether you’re overseeing a historic church, a capitol building, or a decorative interior, taking a proactive approach to mold prevention ensures that these spaces can continue to inspire for generations to come.
