Continuing the Case Against Spray Foam: Understanding the Risks and Better Options
This past week, we started looking at a topic of spray foam used to fill voids, gaps, holes, and even cracks in some cases, in exterior masonry walls. Often, these walls need actual “new” (in most cases, historic brick facades will need salvaged historic bricks, not actually newly manufactured bricks) brick installation or even simply repointing to sustain and preserve the existing building. Instead though we often find people put weird and inappropriate materials into the wall as a temporary stopgap or even as an attempt at a long-term solution.
The picture below shows and example of a an old and abandoned dryer exhaust duct that has been filled with polyurethane spray foam. We looked at the same location in last week’s blog, but as a simple recap, this foam is so deteriorated that when you touch it gently with your finger it just turns to dust. That level of deterioration and compromised condition means that it’s permeable to exterior water and precipitation and provides no effective means of a weather barrier from the outside.
We looked at these details in last week’s blog, but today we’re going to talk about some of the chemical properties of the typical off the shelf, big box store, type spray foams.
Spray foam, like this, while readily available off the shelf in an easy to use can, is not ideal for sealing exterior gaps, voids, or holes in buildings due to its inherent properties and limitations. Polyurethane spray foam is created when two main components – isocyanates and polyols – are mixed, causing a rapid exothermic reaction. This reaction produces a foam that often expands and hardens, to a degree. While this foam does have some insulating thermal resistance properties, its structure is not completely closed-cell, especially in the case of the more commonly available off-the-shelf one-component foams.
The pictures show how some previous contractor applied spray foam around the door jamb, where the door jamb meets the brick. There’s nothing wrong with this type of application on its own, if executed properly, but in this case it’s not well executed. The contractor did not use a masking and did not recess the spray foam or follow up to apply an exterior sealant on top of the spray foam. In a case like this, when executed properly, the spray foam could actually work as a substitute for a backer rod. In most cases though it’s better just to use an actual backer rod.
The mixing of isocyanates and polyols in spray foam products depends on whether it’s a one-component or two-component system. In one-component spray foam, which is typically what you find in off-the-shelf cans for DIY use, the isocyanates and polyols are pre-mixed in the can along with a propellant and other additives. This type of foam starts to cure when it’s exposed to moisture in the air upon release from the can, with the reaction triggered by this moisture exposure rather than by the mixing of components during application. In contrast, two-component spray foam, typically used for larger applications, keeps the isocyanates and polyols separate until the moment of application. These components are mixed in the spray nozzle or gun as they’re being applied, and the reaction starts immediately upon mixing, without needing moisture from the air. The pre-mixed nature of one-component foams is part of why they’re less ideal for creating a perfect seal, especially in exterior applications. The reaction is less controlled and more dependent on environmental conditions compared to two-component systems, which can lead to more inconsistent results in terms of cell structure and overall performance.
The foam’s structure contains thousands of tiny air pockets or cells. In theory, these cells should be closed, forming a barrier. However, in practice, especially with one-component foams, many of these cells are interconnected or partially open. This cellular structure, while beneficial for insulation, can act like a network of microscopic sponges when exposed to water.
When used on building exteriors, this foam can absorb moisture through capillary action. Water molecules can be drawn into the foam’s structure through these interconnected cells, potentially leading to moisture penetration or entry into the building interior. This process can be exacerbated by freeze-thaw cycles, which can further break down the foam’s structure over time.
At the door header below, where the jamb of the door meets the steel lintel which supports the brick facade above, we show an example of sloppily applied spray foam. It was left just like this, for years. This is a historic building, and although the contractor took a half measure approach, at best, the building owners were also unable to find a better contractor, for years, until they met us.
Polyurethane foams are intended to chemically bond to substrates. The isocyanate groups in the foam react with moisture and any hydroxyl groups present on the substrate surface. This reaction creates the chemical bond, but its strength can vary depending on the substrate material and surface condition. On highly porous or damp rotted surfaces, as shown in the pictures below, common in dilapidated exterior conditions, this bond will not be as strong or consistent, leading to potential adhesion failures over time.
Also, as shown in these pictures, polyurethane foam is highly susceptible to ultraviolet (UV) radiation damage. UV rays from sunlight can break down the polymer chains in the foam, leading to discoloration, embrittlement, and eventual degradation. This process, known as photo-oxidation, can cause the foam to become brittle and crumble, (like a ball of dust as shown in last week’s blog) compromising its sealing and insulating properties. The degradation often starts at the exposed surface and progresses inward, increasingly creating channels for water ingress.
The foam’s expansion process during curing can also be problematic in exterior applications. As it expands, it can create pressure on surrounding materials or structures. In confined spaces, this expansion can lead to warping or damage to adjacent building components which leads to unintended openings. For example, in the case of a door or window and the associated jamb trim, as the space spreads open, some parts become filled with the foam which is causing the spreading, but other parts will now have a void or gap.
For exterior applications, specially formulated sealants can be more appropriate. These products are designed to withstand UV exposure, remain flexible to accommodate building movement, and create a seal that is closer to actually being weather-peoof. The best method of preventing improper use or application of phone materials though is to simply apply it properly with masking and or intended recesses so that it can be properly sealed at the exterior with wood trim and or elastomeric sealants.
The series of pictures below show another example of poorly applied spray foam as a stopgap type measure which ended up being left without follow-up for years. Again, the problem with this type of insulation is that the sponge like matrix of the foam works like a sponge which will absorb water from the exterior and wicked inwards into the inside of the building.
In this upcoming week, we’ll take a break from looking at examples of Incorrect and bad installations and instead look at some alternative methodologies to do work better and more professionally.
We can Help
Our company focuses on historic restoration more than modern building upkeep, maintenance, and construction, but our company understands both types of construction very well and a full picture well-rounded approach is needed in any niche in the construction industry. Although we focus on historic restoration, repointing, tuckpointing and historic brick repair, our company also has technical knowledge and competencies in the areas of modern and contemporary construction as well as we become one of the leaders in that area of the market today. Understanding both historic and modern or contemporary construction is useful because both aspects help understand the challenges and potential solutions for challenges in building science and construction.
We can help with a variety of historic masonry restoration needs and upkeep, from modest tuckpointing and or repointing to complicated and extensive historic masonry restoration. Infinity Design Solutions is a historic restoration specialist contractor specializing in both historic masonry restoration such as tuckpointing our repointing, and brick repair. If you have questions about the architectural details or facade of your historic building in Washington DC, reach out and say hello and if we can help we’ll be glad to assist you. You can email us or call us on the telephone at the following link: contact us here.
