As a fabricator of natural and engineered stone, I know there are many adhesives to choose from in order to make your finished product really work, and if you don't use the right adhesives to laminate, seam and set your stone pieces, you may be planting a land mine that can come back to haunt you in the future.
There are many different problems that you, as a fabricator, can create for yourself if you are not using the correct glue or adhesive for the proper application. I had a guy call me this morning, just after I had started writing this article, that serves as a great case in point — he had done a couple of kitchen projects recently, using Absolute Black granite (it's not really a "true granite," but rather a "basalt" — I'll leave that whole discussion for a future article) and he could not figure out why his laminations were getting cracks perpendicular to his glue lines.
After asking a few questions to qualify my suspicions behind the cause of his problem, I told him that the probable cause(s) were most likely two factors: First, he was "torque-ing down" his C-clamps too tightly, and second, after finding out what type of glue he was using, I told him that he should not be using "knife grade" epoxy, but rather "flowing" epoxy when gluing up laminations on 2-cm Absolute Black, or any lamination for that matter. Now bear in mind that this is my opinion after having done slab fabrication over the last 23 years, and what I share with colleagues, clients and students is based on the "this is what works for me" approach.
Do you see what I mean about the problem my friend was having? He had the right idea, but the wrong approach. In fairness to him, he is relatively new to the industry and had not come across this type of situation in the past. He was basically using the wrong kind of glue to accomplish the task at hand. He did not start out with the "right" combination of products to perform his work.
You can avoid another disaster when it comes to laminations by using the correct glue for the appropriate stone type. For many years, I have glued my laminations thusly: Granite gets epoxy and marble/limestone gets polyester — and never the other way around. I was always taught that the oils in epoxy glues will not stain the majority of granites, unlike marbles and limestone, where I have personally seen distinct staining on more than one occasion as a result of using epoxy on these softer stones. Another byproduct of using the wrong setup (polyester to glue laminations on granite countertops instead of epoxy) is that I have also seen many failures. Often, this mistake is made because the polyester was cheaper or it set up faster. I have seen whole laminations that have fallen off of the front leading edge of counter tops — all traceable back to the wrong glue being used to accomplish a very specific purpose.
When it comes to setting individual countertop pieces that make up an assembly, I have seen many products used for adhering stone tops to the substrate or directly to the cabinets. The first slab countertops I ever installed (back in 1985) were set using good old 100-percent, pure silicone rubber. A lot has changed since then, and many guys still use silicone, but I have found other products for specific applications that actually work better and are more cost-effective.
One such product that I have personally been using for a number of years now is "Alex-Plus" latex caulk — don't laugh; it really works. I know there may be some of you that, after reading "latex caulk," are saying . . . what??? I said the same thing when a friend of mine shared this tip with me years ago, but then I started thinking — with the exception of cantilevered overhangs and raised bar tops, the shear weight of granite will hold most conventional 24-in.-deep countertops in place. The latex, when dry, holds the stone and prevents it from shifting laterally, just like any other type of adhesive. The big plus that I can see to using a latex caulk in this kind of application is when you have to return for some kind of repair that entails removal of the top (without damaging it). That is paramount. With silicones or epoxies, you will be taking out the existing top in chunks, and in most cases you'll be looking at a re-fab. This can be a disaster if you have no more of the particular stone left to work with, and in most cases Murphy's Law will kick in and guarantee you a scenario that makes having your gums scraped a lot more attractive.
One more way you can prevent having to go through a potential crisis time and again is to take the time to educate each of your customers in what is considered normal after their stone countertops are installed. This is (in my opinion) best done even before any money changes hands. One of the most common things that uninformed consumers freak out over is spots in the stone as a result of the moisture from the setting adhesive. This happens when the moisture in the adhesive is migrating to the surface of the stone so it can evaporate. When a customer sees the spots the day of or the day after the tops are installed, and the spots stay for a week or two, they will be calling you to complain. That is unless you educate them upfront and let them know the spots they are seeing are a normal byproduct of the setting process and will fade away in time.
In short, the best way to make sure that you are using the right adhesive is to keep on researching and looking for the best possible combination for seams, laminations and setting. And once you have the correct combination, "stick" with it — don't fix what ain't broke!