Caulks, Sealants and Adhesives: Mind the Gaps
authors Emily Blackburn | June 16, 2021
Filling the holes in a project should be a straightforward process for any pro. But those who’ve recently been down the caulks-and-sealants aisle at a local supplier knows that filling gaps can be anything but straightforward.
There are three complicating factors. First, there are many products to choose from today. They really do occupy an entire aisle. Second, there’s the growing trend toward multiple uses for a single product. A product might be appropriate for filling paintable holes while at the same time offering a limited warranty for water and air tightness in subzero temperatures. Third, and potentially most problematic, some manufacturers use the terms “caulk” and “sealant” interchangeably.
Compounding the murkiness is the fear of callbacks. Making the wrong choice could be disastrous with leakage, cracking and peeling only some of the undesirable consequences.
Which is Which?
A pro can be forgiven for using “caulk” and “sealant” interchangeably, as many remodelers do these days. Some, not all, manufacturers do this as well. Caulk is a term that comes from boat building; sealant originated with home builders. Otherwise, they function and are applied in much the same way. So how do you know if you need a caulk or a sealant?
“You look at caulk as, ‘This is what is going to fill a hole.’ There’s not really a performance element along with the product. There’s only a certain level of performance you’re going to be able to get from that type of technology. It fills a gap and you can paint it, and that’s essentially what you’re looking to do,” explains Mike TenBrink, vice president of marketing at Henkle, parent company of OSI, Loctite, LePage and GE brands. “Sealants are mostly used for applications where it matters.”
Many manufactures tend to use “caulk” to describe their base-level products, whereas “sealant” is reserved for high-performance products that receive a lot more high-stress impact, or areas where there is likely to be a predictable degree of expansion and contraction. Sealant is also made to expand and remain malleable and elastic in areas prone to shifting. Caulks tend to be rigid and aren’t meant for areas of the home that expand and contract or experience temperature swings.
Caulk prevents leaks while filling gaps where ceramic, metal or plastic plumbing is installed. Conversely, sealants are formulated for waterproofing bathtubs, shower stalls and countertops. The inherent flexibility of sealant enables the product to maintain watertight seals even in situations with big temperature swings. This makes them ideal for exterior work. Caulk, on the other hand, is prone to cracking when confronted with unstable temperature in addition to drying out over time.
Adhesives, of course, are easier to define and differentiate from sealants and caulks. Adhesives bond two surfaces together. Different formulations make them capable of handling longer timeframes and varying amounts of stress to the bond. Adhesives are intended for high-pressure situations. They are not intended to fill gaps or seal joints.
For the purposes of this article, we are going to use “caulk” to describe rigid, low-stress materials, and “sealant” to describe flexible, high-stress materials. “Adhesive” will continue to be used to describe materials that bond.
“What [sealants and adhesives] adhere to needs to be as diverse as the range of building materials in use today,” and they continue to evolve, TenBrink says. “You can see that in materials like PVC, natural stone and faux cladding. All of these different materials that people are using on the outside of their homes, even as recently as 20 years ago, didn’t exist.
“And now you see all of these different finishes and material types that have different levels of expansion and contraction based on the cyclical temperature changes. So that’s a huge challenge for a sealant. It’s the only thing that stays between two dissimilar building materials and keeps that joint sealed. A sealant must be able to perform. And when you talk about performance, it’s about the level of adhesion to those diverse building materials, but also their ability to expand and contract as those materials expand and contract themselves.”
As a sealing material, silicone is very flexible and water-repellant, making silicone sealants one of the best for windows and bathrooms. Products made from silicones remain durable at all temperatures and are completely waterproof. They adhere to a wide range of substrates but not to the most common building material: wood.
Supreme Silicone from GE is ideal for areas constantly exposed to moisture, especially in kitchens and baths. This silicone sealant offers 100 percent more flexibility than Class 25 sealants and offers 50 percent more joint-movement capabilities without cracking or shrinking, TenBrink notes.
Unlike silicone sealants, polyurethane-based products have a much higher abrasion and tear resistance when compared to silicone, making them more useful for high-traffic, albeit temperature-controlled, areas. They dry instead of curing. This results in a denser, harder result than silicone-based sealants.
In short, polyurethane caulks and adhesives are very durable.
“The use of polyurethane adhesives continues to see steady growth in a variety of building and construction applications, including subfloor installation,” says Jason Wirth, senior director of project management for DAP.
Water-based products adhere well and offer movement capability. Most are acrylic latex, a kind of plastic or synthetic polymer chemically dispersed in water. These products are thought to be as flexible as silicone-based sealants in terms of their versatility in a range of applications. One has to be careful when applying water-based caulks, however, as humid conditions can slow curing, and rain or other water contact can wash them away before they are fully cured.
“Water-based technology is getting more and more advanced as contractors demand sealants with superior performance matched with ease of use, paintability and VOC requirements,” Wirth notes.
The products that are getting the most attention, however, are the hybrid sealants and adhesives.
“Silicone and polyurethane adhesives and sealants have been on the market for years, but as pros know, these products can have limitations. Hybrid technology has been developed to fill these performance gaps,” Wirth says. “Typically, ‘hybrids’ today are a sealant or adhesive that takes elements from both silicones and polyurethanes to create an exceptional performing sealant that accepts paint and offers excellent durability, adhesion and overall performance. These products are often referred to as ‘hybrids’ or ‘modified polymers.’”
OSI’s QuadMax, a window, door and siding sealant, for example, offers maximum durability and application performance with strong adhesion to all materials with enhanced resistance to UV, dirt, dust and extreme temperatures and proven wet-surface application. QuadMax is made from SMP technology—silane modified polymers. These moisture-curing elastic solutions can function as both sealant and adhesive, with one and two component solutions. SMPs boast excellent adhesion to most substrates, as well as UV and weathering resistance. Defined as a sealant, it features five-times stretch and Class 50 joint movement capability for long-term durability.
While hybrid technology is prevalent in the sealants market, this technology is also becoming much more prevalent in the adhesives market as well, Wirth says.
Loctite PL Premium Max, another SMP-based material, is a construction adhesive that boasts reliable high-strength, long-term strength on most substrates and can be applied to wet and frozen surfaces, as well as in temperatures between 10 degrees and 120 degrees Fahrenheit.
DAP offers DynaGrip Heavy Duty MAX, a premium hybrid adhesive that delivers five-times faster bond strength for heavier applications where bond strength and cure speed are critical.
“I think one of the main trends that we’re really seeing in the residential market is this liquid applied flashing that can be used for a lot of different air sealing or moisture control in the wall assembly,” explains Kaylen Handly, technical innovation manager for Benjamin Obdyke. Liquid flash is a fluid-applied flashing membrane made of STP-E (silyl-terminated polyether) or STP-U (silane-terminated polyurethane) technology. It is moisture-curing, combining the durability of silicones with the toughness of polyurethanes.
“It makes it a lot easier for the contractor to use it in many different locations, whether that be transitions between two dissimilar materials, like at the foundation to the wall system or to integrate the windows and doors with the rough opening and the WRB.” Handly notes that 15 years ago there were a lot more asphalt-based flashing tables and mechanical flashings used with metal.
Benjamin Obdyke’s Hydroflash LA is designed for exterior flashing of rough openings, transitions and seams as part of a high-performing air and water management system. It’s ideal for sealing geometrically challenging areas to create monolithic sill flashing and prevent air and water leaks. A class 50 sealant, it has great stretchability when it comes to expansion and contraction.
Similarly, Zip System Liquid Flash from Huber Engineered Woods provides an alternative to traditional gunned sealants and physical flashing options because it flows easily to seal difficult areas, such as rough openings and wall penetrations; bonds and cures in wet weather and on damp substrates; and becomes waterproof after installation. “We’re going to continue to see a versatility in how builders use sealing solutions such as caulk, sealants and adhesives,” says David Wescott, general manager of accessories for Huber.
Versatility is key when it comes to the hybrid options. Where the caulk-versus-sealant debate could mean an improperly sealed window frame or shower stall, hybrids offer peace of mind in that they can be reliably applied in more locations without worry of leakage or cracking. “[There’s a] higher emphasis on hybrid and water-based technologies due to low VOCs. They also have less odor for indoor applications and are easier to tool [and] use,” explains Abbe Raabe, director of product marketing for Titebond.
“What I see the most is people are looking for performance. Remodelers are looking for performance. They just want to use the sealant that’s going to work especially as, in this category, you can get overwhelmed by a saturation of claims,” TenBrink says. He notes that while hybrid sealants and adhesives may come with more of a premium price tag, they are worth it for remodelers who are able to limit callbacks and bad reviews due to the “premium” performance.
“Updates to statewide building codes and more builder interest in building to higher standards like Passive House are affecting the production of sealants and also how the industry is using them,” Wescott says.
When it comes to ensuring homes aren’t leaking air or letting moisture in, complying with the International Energy Conservation Code (IECC) is the first place to check.
The 2021 IECC recently passed, mandating continuous exterior insulation in Zones 4 and 5 in the United States, where previously there hadn’t been any requirements. This goes hand-in-hand with their “fat” (R-30) cavity insulation requirements for Zones 6, 7, and 8.
“We’re looking at putting a minimum of 1 inch insulation on the exterior of your sheathing, and that dramatically complicates the window details,” Handly explains. “Now, everything’s bumped out that extra inch, and it adds a lot more irregularities to our normal, rough opening. This is where a product like [Hydroflash LA] has really gained a lot of traction because we can seal those different gaps.”
Handly goes on to explain that the codes are forcing installers and remodelers to be very precise with their installations. “We’re putting a blower door fan on the front door, and we’re creating a vacuum on the entire house; and with that, they can calculate the air leakage. If you don’t hit a certain threshold, you have to go and find what’s leaking and reseal it.”
The additional insulation requirements are making waterproof sealing even more important because there isn’t the same drying potential as when the R-value of the wall is lower, so if any moisture gets behind the sheathing, it’s a recipe for disaster.
As has become common for the COVID-era, remodelers are finding the most valuable trend to come out of the last year has been the increased focus on education and training.
For some, it means revamping an app, such as Bostik’s Pro mobile app, which was “built for the time-constrained contractor to efficiently get them the product information, technical data and key videos that they need on the jobsite or wherever they may be,” explains Eric Loferski, Bostik’s director of marketing. The app includes technical and safety data sheets as well as a full media center with how-to videos to assist contractors on the job.
For others, education has taken a much more hands-on approach. “A lot of the success that we’ve been having is with virtual jobsite installation, where I’ll actually talk with the contractor and architect beforehand. We’ll discuss the details and different layering that they’re putting together,” Handly says. “Then I can physically build that here in our warehouses and then walk through step-by-step the process on how to integrate that with the flashing component and the window.” QR