Paint delamination can be a disruptive and costly failure that can occur during a restoration or renovation project. What makes it especially frustrating is that it typically occurs after a new paint system has just been applied, turning what appeared to be a stable surface into a peeling, cracking problem. The causes are rarely obvious, and without knowing the root issue, any repair is likely to fail again.
At John Canning & Co., we’ve responded to paint delamination conditions across many historic landmark buildings and in nearly every case, the failure traces back to one (or more) of four key causes. Let’s break down what paint delamination is, the root causes, and how to remedy the issue.
What is Paint Delamination?
Paint delamination is what happens when paint loses its bond to the surface beneath it — separating, bubbling, or peeling away from the wall or ceiling it was meant to protect. It’s a condition that can appear suddenly and spread quickly, but in most cases, it’s been quietly developing for years beneath the surface. For historical buildings in particular, where layers of paint may have accumulated over decades or even centuries, delamination is rarely a simple fix, but rather a signal that something deeper needs to be understood and addressed.
Why Does Paint Fail During a Restoration Project?
As a company with significant experience in the historic preservation field, most notably in historic finishes, over the years and more frequently than we can count, we have observed and assisted with paint delamination conditions. This includes situations where a new specified paint system is applied to the walls and ceilings, and the paint is delaminating from the substrate. We often see paint fail during a restoration project when the existing paint coatings appear to be generally stable. Our studio is often called in to assist project teams to determine why paint is failing, especially when the project is moving towards completion and paint-work is either underway or was recently installed. When it comes to determining specifically why there is paint delamination, there are generally four potential causes for why the paint is failing. The following is a summary of each of the failure types. Any one of these, or a combination of them can be the likely cause of a failure.
Typical map cracking and paint delaminating.
Types of Paint Failures:
Saponification of Paint
Saponification of paint is a chemical reaction that occurs when newly plastered substrates are painted with oil paint.
Newly plastered substrates have high alkalinity until they have cured to a neutral ph. If new oil paint is applied to a surface with high alkalinity, there will be a hydrolytic break down of ester bonds. Ultimately, this chemical reaction creates a thin powdery film (soap) between the plaster and paint, thus affecting long-term durability and adhesion.
Over time and sporadically, paint will often delaminate in isolated locations. This will take place until there is a larger event, at which time a catastrophic failure will occur.
Thermal Shock
Modern buildings have reasonable and generally consistent environmental controls i.e., heating and cooling systems. These systems typically, at a minimum, regulate humidity and offer a steady climate control. When a building is shut down for an extended period without climate control, the building’s temperature and humidity are not regulated. Thus, when the building returns to a typical state and is climate-controlled, many substrates experience thermal shock. This is especially evident at materials that expand and contract rapidly and have a greater thermal coefficient.
In the case of thermal shock, paint film could be expanding and contracting at a different rate than the plaster and framing behind it, which can lead to a separation or weakening of the paint bond to the plaster substrate.
New Paint Coatings & Multiple Existing Paint Layers
Modern paints, especially acrylics, are meant to adhere to the layer the paint is applied to, much like a glue. Whereas traditional oil paints were applied in a thinned-down fashion, meant to penetrate the substrate as much as possible. This required multiple coats of oil paint to create a solid and opaque paint film. This use of traditional oil paints in today’s construction is too costly in both material and labor. Therefore, the advent and development of acrylic paint has superseded oil paints, for these obvious reasons.
Generally, acrylic paints have high adhesion and bond very well to paint layers below it, as is the case here. However, when acrylic paint is applied (which has water in its formula), it will penetrate (to an extent) and soften the previous layers of paint on the substrate, even if only briefly, until the paint dries and evaporates. As this acrylic paint dries, it will shrink. As it shrinks, its bond to the paint layers beneath it becomes stronger. This shrinking often has a greater tensile pull and bond than the old paint used on the substrate. It is quite possible that the new paint being applied is literally pulling the old paint off the wall. This could be especially true if the old paint systems are compromised with thermal shock and/or saponification, as outlined above.
Sometimes, certain building spaces are painted very frequently and often with low paints. This means these surfaces have an incredible buildup of paint film over the decade. It is quite possible that there are 30-50 paint layers in any given room in these types of spaces. These paint layers may not all be compatible with each other, and could cause complications with any new paint system. The sheer cumulative weight of all these paint layers, being held up by the initial paint layer, may be a contributing factor to catastrophic failures.
Age of Original Paint
If the original paint coatings are old (i.e., approx. 100 years old), they could have quite possibly surpassed their serviceability. Any of the aforementioned, on their own, can be the cause of this catastrophic failure. The application of new paint, regardless of its type i.e., acrylic or oil, would not mitigate current or future failures.
Saponification, thermal shock, the multiple existing paint layers, and the age of the original paint coating as fuel, and the new paint coatings can be an igniter to paint delamination problems. Having someone experienced in historic finishes can tell you and guide you whether if one, a combination or all of these causes are contributing factors.
Examples of Typical Paint Failures
Remedies:
When it comes to paint delamination remedies, three basic paths can be explored.
- Remove all coatings down to the plaster substrate, thus mitigating any potential for failure. This is an excellent but costly approach. It also requires a significant amount of time.
- Encapsulation. There are several encapsulant candidates that you may want to consider:
- Dry Wall Application. Apply drywall to the surfaces with adhesive and fasteners, followed by typical joint taping and new paint coatings. This is an excellent approach, as it creates a permanent barrier between the new paint and the old coating system.
- Nu-Wal Plaster Restoration System by Abatron or similar. This elastomeric coating system is reinforced with fiberglass mat. This will bridge and conceal paint craters, cracks, and coatings. However, labor will be required to scrape loose paint. The thought behind this system is that while paint may continue to delaminate behind the mat in isolated locations, the Nu-Wal flexible elastomeric system will act as a bridge over this condition. This system will likely be faster and less expensive than drywall; however, it will not be as foolproof.
- Reinforced Plaster Veneer. With this approach, the walls are prepared by removing loose/peeling paint, followed by chipping the surface with mallets to create small craters throughout the surface. These craters act as a key to the new plaster it will receive. Once chipped, the entire surface receives a bonding agent followed by an application of fiberglass mesh, such as that used for EFIS systems. This would also be followed by two applications of plaster veneer, such as USG Imperial or Diamond brands. This can be a long-term, durable solution. Vinyl or canvas wall covering. Similar to Nu-Wal, this will bridge and conceal paint craters, cracks, and coatings. However, labor will be required to scrape loose paint. This system will also likely be faster and less expensive than drywall, but not as foolproof.
- A foolproof remedy to mitigate paint delamination is full paint removal with chemical paint strippers. This can be an effective solution, but not without its own considerations. Once paint is completely removed, the installer must ensure the chemical stripper is fully removed from the substrate, leaving absolutely no residue. They must also confirm the substrate has a neutral pH. Our restoration specialists have used Smart Strip Advanced Paint Remover by Dumond Chemicals.
How to Prevent Paint Delamination in Historic Buildings
1. Have a Paint Investigation Performed
Before applying any new paint to a historic building, commission a historic paint investigation and get an assessment of the finishes. Understanding what’s already on the walls ie.) how many layers, what types of paint, and their current condition, is essential to choosing a compatible system and avoiding costly failures down the road.
2. Maintain Consistent Climate Control
Fluctuations in temperature and humidity are among the leading contributors to paint failure. If your building is closed for an extended period, keep environmental systems running at a reduced but stable level. Bringing a building back to full climate control after a long shutdown should be done gradually whenever possible.
3. Allow New Plaster to Fully Cure
If any plastering work has been done, be sure it has fully cured and reached a neutral pH before painting. Applying paint, especially oil-based paint, to fresh plaster is one of the most common and preventable causes of delamination.
Work With Specialists Who Know Historic Materials
While paint delamination can seem overwhelming, John Canning & Co. has worked in Historic Landmark buildings throughout the United States, both as historic preservation consultants, conservators, and specialty contractors. We bring decades of hands-on experience in historic paint finishes and preservation to every project we touch. If you’re seeing paint failure in your building, don’t wait for a small problem to become a disastrous one. Reach out to our team today — we’d be glad to help you find the right path forward.
