Polyurethane adhesives are popular in residential construction due to their bonding strength, durability and ease of use. One critical factor often considered while selecting such adhesives is their drying or curing time, which can significantly impact project timelines and productivity. This article will delve into the mechanisms and factors affecting the drying time of TYTAN Professional polyurethane adhesives.
What you will learn from this article:
Understanding Polyurethane Adhesives
Polyurethane adhesives are generally known as ‘reactive adhesives’. This means they undergo chemical reactions to transition from a liquid or semi-liquid state to a solid state (1). In this case, the reaction is with moisture, either in the air or from the substrates being bonded. These adhesives react with the moisture to form strong chemical bonds, creating a tough adhesive layer. Our Subfloor Adhesive, for example, will dispense from the can as a gel then expand and harden.
This image shows one of our adhesives curing on the left, and on the right you can see the fully cured bubbles:
The drying time of polyurethane adhesives is primarily governed by the rate of this reaction. A common misconception is that higher ambient temperatures will accelerate this process. Earlier this month I met a home builder at the Texas Sunbelt Builders Show in Fort Worth that thought this. In reality, it’s the humidity that plays a more substantial role (2). Increased humidity will provide more moisture for the reaction, accelerating the curing process. We get frequent reports from customers in humid climates that align with this.
In the below Will It Foam Bond 60 video (the section I’m referring to starts at 1:49), our product manager describes how the humidity impacts the curing process. In the case of this video, it was a low humidity day, resulting in a longer curing process:
According to a study published in the International Journal of Adhesion and Adhesives, a typical one-component polyurethane adhesive can take between 24 to 48 hours to fully cure at room temperature and average humidity conditions (3). This duration can reduce to several hours in high humidity environments or extend beyond two days in extremely arid conditions.
TYTAN Professional Adhesives are all within the 24-48 hour window described above. With Subfloor Adhesive and Drywall Adhesive being 48 hours to fully cure, and Foam Bond 60 fully curing in 24 hours. Even more impactful for our customers, however, is the skin time. The skin time for Subfloor Adhesive and Drywall Adhesive is 20 minutes. The skin time for Foam Bond 60 is even faster at 2-5 minutes. The below section describes the difference.
Skin Time vs Dry Time
Two frequently used terms in the sticky world of adhesives are “skin time” and “dry time”. They pertain to distinct stages of the curing process of polyurethane adhesives. Skin time refers to the period it takes for the adhesive’s surface to form a solid “skin,” sufficient to be resistant to minor touch or light pressure, but the adhesive beneath this skin is still not fully cured (4).
This timing is key in residential construction because it gives the applicator time to apply one substrate to the other. For our Drywall Adhesive, that 20 minutes allows the drywaller to apply the adhesive and then apply the sheet of drywall.
On the other hand, dry time or curing time is the period required for the adhesive to fully harden and achieve its maximum strength. This entails the complete evaporation of solvents and the reaction of the adhesive with moisture, allowing the formation of robust chemical bonds (4). It’s crucial to note that while skinning may occur in minutes or hours, curing time takes longer (as described in the previous section).
Additional Factors
Application thickness is a crucial determinant of the curing time of polyurethane adhesives. When applied in a thick layer, the moisture necessary for the reaction that enables curing takes more time to penetrate to the core of the adhesive, thereby slowing down the curing process (5). The study by Oko and colleagues indicated that, for polyurethane adhesives, an increase in application thickness led to a significant extension in curing time due to the moisture diffusion constraint. What we recommend is applying a thin and uniform layer of adhesive. Using too much adhesive (is more adhesive better?) will result in an inefficient curing process.
The kind of substrates being bonded also affects the curing time. If the material absorbs moisture, this can lengthen the drying time as they compete with the adhesive for available moisture (6). On the other hand, moisture-resistant materials can lead to faster drying times as they leave more ambient moisture available for the adhesive. A future area of research here could be on how surface energy (low or high) impacts drying time.
To summarize, the drying time of polyurethane adhesives is a complex interplay of factors such as ambient humidity, application thickness, and substrate type. While typical drying times range from 24 to 48 hours, understanding these factors can help adjust timelines and optimize the bonding process. It is always recommended to refer to manufacturer instructions for specific drying times of the product being used.
The choice of adhesive in construction will depend on the job’s requirements, but for the majority of applications, polyurethane adhesives are an effective solution. Our TYTAN Professional polyurethane adhesives ultimately cure by reacting with moisture present in the environment or the materials they bond. Check out this article I wrote about the curing process. Various factors come into play, such as the humidity level, temperature, adhesive thickness, and the types of surfaces being adhered.
If you are interested in learning more about our polyurethane foam adhesives or have questions about a specific application, please reach out to your local TYTAN Professional Representative. You can also give us a call at (817) 381-4427.
Sources
- Britannica, The Editors of Encyclopaedia. “polyurethane”. Encyclopedia Britannica, 15 Feb. 2023.
- Polymer Science Learning Center, Making Polyurethane Foams
- Mishra, Rath, Nayak (2019). “Moisture Curing of One-Component Polyurethane Adhesives: Kinetics and Mechanisms”. International Journal of Adhesion and Adhesives.
- Gooch, J. W. (2011). Encyclopedic Dictionary of Polymers. Springer.
- Oko, A.E., Anigbogu, C.O., Okafor, V.O., Onuegbu, G.C., & Onuegbu, T.U. (2013). “Influence of Thickness on the Drying Time of a Polyurethane Adhesive”. International Journal of Adhesion & Adhesives, 44, 48-51.
- Gledhill, A., Kinloch, A. J., & Sprenger, S. (2013). “The Adhesion of UV-curable Adhesives to Polypropylene Substrates”. International Journal of Adhesion and Adhesives, 46, 39-46.
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