Stone World had the opportunity to talk with Integra Adhesives about all things adhesives including chemical make-up, the difference in the various types offered, and how technological characteristics of these products have evolved in recent years

Stone World: I know this can be a complicated question, but a question I get a lot is, “How do adhesives actually work?” They get that two things stick together with the use of an adhesive, but what is actually happening that creates that bond?

Integra Adhesives: There are two types of adhesion — mechanical adhesion and chemical adhesion — and adhesives in our industry do a little bit of both. Our glues are applied as a liquid then cure and become solid.

Mechanical adhesion occurs when the liquid glue flows into crack, holes and other imperfections on the stone surface. Once it cures and solidifies, it cannot “flow” or change shape so it is wedged in those cracks and holes.

Chemical adhesion occurs when active molecules/groups in our formulations react with chemicals on the surface of the stone. Since this forms actual chemical bonds, it is not dependent on the surface shape and tends to be the stronger type of bond.

Unfortunately, the reactive groups that our glues can bond to aren’t evenly distributed on the surface of the material — especially in natural stones. That’s why it’s beneficial to have good mechanical adhesion as well. Having both chemical and mechanical adhesion present is what results in the strongest bonds.

Where porous surfaces may fail to bond is typically the result of a lack of chemical adhesion and where smooth polished surfaces may fail to bond is typically the result of a lack of mechanical adhesion.

How have adhesives changed over the past 10 years or so?

Adhesive technology has changed along with the needs of the industry. We’re seeing greater demand for accurate, consistent color matching — especially in the trending white quartz/stone design palettes. White adhesives need to be much closer than most other colors in both tint and concentration. Any deviation from this can result in a visible line, which is quite pronounced on stark white surfaces.

We offer a wide color palette, including whitest whites, for the best color matches of today’s demanding surfaces.

Interior design is seeing countertop slabs being applied vertically for walls and fireplaces, and large waterfall edges, so adhesives have had to adapt to increase shear strength and reduce sag after application. Demand for outdoor installations has also forced adhesives to adapt to weathering conditions and ultraviolet exposure.

What can fabricators do for the strongest bond possible with whatever adhesive they are using?

The first point is to make sure to use the correct adhesive for bonding. Seaming adhesives are not intended to bond to metal, wood or to provide structural support. And carefully follow the instructions provided by the adhesive supplier. This is particularly important for proper cartridge piston leveling, purging and dispensing.

Rougher surfaces will increase surface area and improve physical adhesion. Getting full coverage of the surfaces to be bonded is key to forming a strong bond. In order to ensure completely whetting out the surfaces, when using a non-sag adhesive it should be dispensed into the middle of the seam, whereas a high-sag adhesive should be dispensed at the top of the seam. Squeeze out of excess adhesive along the top of the bond line is a good indicator of having the proper amount of adhesive and proper whetting of the surfaces to be bonded.

Properly cleaning the surfaces to remove any dust or contaminants will make sure any available active groups we can chemically bond to aren’t blocked for chemical adhesion. Having a properly cleaned surface is probably the most important thing.

Avoiding bonding to cold stone or using cold adhesive will help improve bonding. The adhesives used in our industry generate, and require, heat to cure. If the substrate is too cold, the reaction may not go to completion and that WILL result in lower bond strengths. Also, ensuring the stone surface is dry will aid in forming a strong bond.

Integra Adhesives products are qualified using rigorous mechanical testing using proven methods on various substrates to verify their strength and versatility on various surfaces.

Integra’s adhesives do not require undercutting or extra surface preparation other than simple surface abrading.

How about for a miter, anything special/different they should do to have the strongest miter possible?

The process is mostly the same. Some fabricators think that increasing the miter angle will assist in bond strength, but in actuality, the seam widths should be the same as with a lamination or a deck seam. Miters should be kept under 45.5°. Other than that, the process is mostly the same.

What are the benefits of using a cartridge-type system for adhesives versus some other system?

Cartridges guarantee the correct mix ratio every time so you will not only get the best strength possible for the formulation, you will also have repeatability between cartridges. The mix tips will also help to ensure an even distribution of adhesive along the seam (no big puddles or missing areas). Cartridges also offer ready-mixed colors for perfect matches every time rather than hand-mixed colors in bulk systems that will vary from fabricator to fabricator and job to job. Cartridges offer much greater consistency over bulk systems in both cure, bond strength and color. The cartridge system also offers ease of use and reduced health and safety risk due to reduced exposure.

What special/different things should a fabricator due when rodding a countertop? If anything.

Making sure to choose the right adhesive for the job is the first step. Fiberglass rodding is the ideal material of choice. Fiberglass won’t rust, isn’t prone to expansion and contraction, and won’t be visible through lighter-colored surfaces. Cutting the channel to the appropriate size is also key, and using an adhesive that’s designed for gap filling tolerances that complement those dimensions. Adhesive tends to shrink during cure, so cutting a channel that is excessively large compared to the rod leaves more room for material shrinkage, which can result in cracked stone.

Anything else you want to mention about adhesives that fabricators should know?

While methyl methacrylate (MMA) adhesives are known to have a distinctive odor, these adhesives are classified as non-toxic and fabricators are urged to refer to the Safety Data Sheet (SDS) for specific health and safety risks before using. We have found Integra MMA adhesives to bond to a variety of surfaces, including the new porcelain and compact sintered stones.