Choosing A Construction Adhesive Technology

What is an adhesive?

Adding construction adhesives is an ideal way to build durability, performance, and long-term holding power into applications where two surfaces need to come and stay together. Construction adhesives provide an efficient and effective way to bond multiple materials, often reducing the number of fasteners required and providing a more uniform distribution of load and stress than fasteners alone.  Some of the more common adhesive applications include subfloor installations, stair assemblies, molding and paneling, bathroom installations, and landscaping. Adhesives can also fill gaps and cover wide and uneven surfaces.

Are adhesives and sealants the same?

While both technologies share some similar characteristics, adhesives and sealants are inherently different in what they do and how they do it. Think of it this way: adhesives are formulated to provide bonding power while sealants are designed to provide long-term protection against the elements by filling gaps and flexing through seasonal changes. For this reason, high-performance sealants typically have lower bond strength and higher elongation. Adhesives, on the other hand, provide high strength with less flexibility. 

How do adhesives work?

Adhesives form bonds, or stick, in one of two ways, depending on the surfaces they are bonding.

• The first, mechanical adhesion, occurs when two porous substrates -- like wood and concrete -- are bonded together. The fibers and pores of the substrate physically become interlocked with the adhesive. When the adhesive dries, the two substrates are then anchored together.  
  
• The second, specific, also known as chemical adhesion, uses molecular forces, polarity, and surface energy to develop a bond between the adhesive and the substrate. This type of adhesion is what must happen when bonding non-porous surfaces, like plastic, glass or steel.

Construction adhesives also dry in different ways, depending on their formula:

• Water-based latex and solvent-based adhesives go through a physical drying process, where the water or solvent in the formula evaporates.  
• Polyurethane and hybrid polymer adhesives are moisture curing. They dry by going through a chemical reaction with the moisture in the air or the substrate.

Moisture curing changes the chemical content of the adhesive, but does not reduce the volume, so there is no shrinkage. With latex and solvent-based formulas, the water content in the adhesive evaporates out, sometimes causing a volume shrinkage of >22%.

Installers must consider several factors when choosing an adhesive for their project, including 1) the type of material the adhesive will be applied to, 2) the environmental conditions during application and the 3) adhesive’s performance characteristics. Let’s look at each of these in more detail.

Materials & Surfaces

First, you need to consider what surfaces will be bonded together. Are they porous or non-porous?

Construction adhesives work best when one of the surfaces is porous, but there are some adhesive technologies that can work for all non-porous surfaces:

• Latex adhesives must have a minimum of one porous surface.
• Solvent adhesives work for both porous and non-porous surfaces but are NOT recommended for polyethylene, polypropylene or polystyrene based materials.
• Polyurethane adhesives work for both porous and non-porous surfaces but are NOT recommended for use with rigid polystyrene.
• Hybrid adhesives – which often combine the speed of an instant grab formula with high strength – work for both porous and non-porous surfaces. They are NOT recommended for some rubbers or flexible sheet goods.

Environmental Conditions

Next consider the environment where you’ll use the adhesive. Is rain in the forecast? Is it hot and humid or dry and cold? Curing and long term performance will be impacted by the temperature and relative humidity, so you will need an adhesive technology designed to address these factors. The adhesive you choose to use in a functioning, in-use bathroom will likely be different than one that is still under construction.

Also, consider if you will be applying the adhesive outdoors or inside. Some adhesives are low odor, making them the right choice for occupied spaces.

Performance Characteristics

Finally, consider how you want the adhesive to perform. Are you looking for an instant hold or do you need the ability to reposition the material for several minutes? For example, consider the application of a chair rail in a home. Having some working time can aid in leveling and overall application.

The most important performance characteristics often include:

• Bond strength: How strong does the bond need to be?
• Permanence: Will the bond ever need to be broken?
• Working time: How fast will the bond be created? Will you need to hold the materials in place or brace them in some way?
• Flexibility: Does the bond need to remain flexible for expansion/contraction? For example – will it be used outdoors and need to respond to seasonal changes?

Certain adhesive products may indicate their intended usage: look for labels specifying applications such as molding and paneling, tub surrounds and landscaping.

What’s the right adhesive for your next project?

There’s a lot that goes into selecting the right adhesive – and the choice you make could depend on the situation at-hand. Installing subfloors on a dry, sunny day is very different than installing them on a cold, rainy one. Paying attention to these considerations can help you get the bond you need for a secure, long-lasting finish. 

But remember, if you’re ever stuck when it comes to adhesives, give us a call. At OSI, we have product applications specialists ready to help.