When it comes to choosing an adhesive or sealant for your specific application, the task can seem overwhelming with so many different products on the market today. Although the two terms are sometimes used interchangeably, there are some critical differences that should be noted before making your selection. In this article, we will discuss the specific properties of both and their unique applications to confidently equip you with the information you need to grant your “seal of approval” and stick with it!

Sealants

Sealants are designed to eliminate gaps between surfaces and prevent things like dust or dirt from getting in. Due to the tight molecular structure of sealants, they are particularly effective in keeping moisture in or out of the components in which they are used. With a paste-like consistency that allows filling of gaps between substrates and minimal shrinkage after application, sealants contain fast-drying resins and epoxies that form a slick finish. Despite not having great strength, they provide thermal and acoustical insulation and may serve as fire barriers. Also used for smoothing or filleting, sealants are generally malleable and have high elongation when compared to adhesives. Commonly applied with a caulking gun or specialized applicator, multi-component sealants are composed of a base and applicator component. The activator is typically added to the base component and mixed for a set period of time before application. Single-component sealants, on the other hand, are commonly packaged in a cartridge and require no mixing or special equipment for application.

Sealant Types and Usage

Sealants are often used in joints between individual stone or metal panels, between stone panels and flashing, at expansion and coping joints in masonry, around window and door openings, and in joints at horizontal surfaces. The most common types of joint sealants include acrylics, silicones, polyurethanes, polysulfides, latex and butyls.

• Acrylics – Frequently used in residential and light commercial construction; suitable for both interior and exterior applications such as windows, doors, woodwork trim, walls, ceilings and electrical switch plates. Advantages: Paintable. Disadvantages: Exhibit a short open-time and can be difficult to cure or tool. Tend to shrink and distort over time. Not recommended to guard against water penetration.

• Silicones – Used in protective glazing systems and insulating glass units to improve thermal performance (minimize heat loss). Advantages: Excellent UV and heat stability, as well as low temperature resistance and high joint movement capabilities. Remains strong and flexible without peeling, cracking or distorting. Maintains a waterproof barrier, making it a good choice for showers, bathtubs, sinks and toilets or outdoor wet-weather conditions. Disadvantages: May stain some types of natural stone without primers and cannot be painted. Can take a considerable amount of time to fully cure.

• Polyurethanes – Typically used in industrial and commercial applications such as decking and flooring. Advantages: Paintable and bonds well without a primer to a variety of surfaces including masonry, wood and metals. Flexible and may be formulated for good UV, corrosion, chemical and water resistance. Seals and mends fiberglass extremely well. Disadvantages: Cannot be used in structural glass assemblies.

• Polysulfides – High performance sealants designed for joints that need to withstand prolonged immersion in liquids. Particularly useful in swimming pools, fountains, fuel and chemical storage tanks, or other locations where submersion must be tolerated. Advantages: Water and chemical resistant. Disadvantages: Requires a primer on almost all substrates and poor recovery limits their use in joints with high cyclic movements.

• Latex – Mainly used in residential and light commercial construction applications; best suited for interior finish applications. Advantages: Excellent paintability with latex paint. Water-based, easy to apply, cleanup and tool. Disadvantages: Should not be used for applications undergoing significant cyclic movement or for high-profile structures.

• Butyls – Excellent for outdoor applications and well-suited for applying on concrete, brick and stone. Effective on chimneys, gutters, flashing and aluminum siding. Sometimes used in curtain wall applications where adhesion to rubber compounds is needed. Advantages: Exceptional weathering properties, adhesion to most substrates and water vapor transmission resistance. Disadvantages: Stringy and difficult to apply. May not be suitable for UV exposure and limited movement capabilities. May harden and crack over time on exposed surfaces.

Adhesives

Adhesives are designed to permanently bind one surface to another, serving as a sort of “industrial glue” for a variety of applications. Although adhesives are more rigid, durable and powerful than sealants, they can be nearly impossible to remove. Generally comprised of more complex structures engineered to grip and bind on a cellular level, they require a better adhesion to surfaces in order for them to hold properly. Consequently, the surface must be thoroughly cleaned and/or specially treated to ensure a secure and long-lasting bond. Available in spray and paint formulas, adhesives will not always dry properly when used on an exterior surface.

Adhesive Types and Usage

• PVA (White/Yellow Glues) – For use on porous materials such as wood and paper. Advantages: Boasts a long open time and reversible bond with applied heat or moisture. Water-based and easy to cleanup. Dries clear. Disadvantages: Curing time can take up to 24 hours and items being bonded must be clamped together or weighed down for a minimum of 30 minutes. Not recommended for outdoor use since standard PVA adhesives are not water-resistant.

• Solvent Cements – Used to join PVC pipes, polystyrene and acrylic plastics. Advantages: Quick set and cure time with a very strong bond. Disadvantages: Will dissolve or distort thin materials and is generally not reversible. Solvent cement must be used and stored away from volatile or combustible products, heaters, pilot lights, open flames and other sources of heat. This product can explode and start a fire if it is used in the vicinity of combustible substances.

• Epoxies – Bonds to most substrates including metal, plastic, glass, ceramic, wood and many types of rubber. Advantages: Extremely strong and highly durable. Resistant to chemicals and able to resist creep under sustained loads. Various curing systems are available for specific applications. Disadvantages: Nonreversible and must be clamped while setting.

• Cyanoacrylates (“Super Glues”) – Bonds well to a wide variety of substrates, especially plastics. Advantages: Exceptionally strong bond. Cures instantly on contact with mated surfaces. Disadvantages: Poor shock or impact resistance (brittleness) and poor gap filling abilities.

• Contact Adhesives – Bonds heterogeneous materials such as wood and plastic or metal and plastic. Advantages: Adheres to almost anything, even non-porous materials. Offers instant joint strength development and flexible bonds due to elastomeric base polymer. Disadvantages: Immediate set does not allow for repositioning.

• Polyurethanes – Bonds both porous and nonporous materials such as wood, metal, rubber, leather, tile, glass, concrete, brick and many plastics. Advantages: Waterproof; Will set well in a wide range of temperatures and high moisture conditions. Requires no mixing, does not contain solvents and can be sanded, stained or painted. Disadvantages: Not as strong as epoxy, setting times can vary considerably and polyurethanes must be handled very carefully.