Beware of Countertop Failure Caused by Rust

Editor’s Note: This month, Jim Heaphy celebrates 20 years writing for KBDN. All of us at KBDN congratulate him on this milestone and thank him for his important contributions to the magazine over the past two decades.

It’s been 20 years since I started writing this column on countertop fabrication. I hope my readers have gained some useful understanding of countertop issues through my writing.

To commemorate this anniversary, I’m inviting my son, James, to collaborate with me on this column. James is a talented stone repair technician with valuable insights about how to avoid problems with natural stone countertops. He is also knowledgeable about solid surface, quartz, butcher block and concrete countertops.

Cracking and Rust

Sometimes a countertop fabrication technique intended to prevent a certain problem can inadvertently cause a more serious problem. Natural stones are brittle and the narrow strip of material that runs along a sink cutout or a cooktop cutout is obviously a potential weak spot, especially during the process of transporting or installing a countertop. If a countertop isn’t moved gingerly the stone could crack across that narrow strip.

The first time that we saw a different kind of problem, we were shocked. This countertop did not have a short crack across the narrow strip in front of the sink. Instead, there was a very long and ugly crack right down the center of the narrow strip in front of an undermounted stainless steel sink.

What could have caused such a failure? It seemed counter intuitive; the countertop should have cracked perpendicularly across that strip, if it cracked at all. Operating on the principle of boldness and self confidence, we agreed to try to solve the problem, hoping to learn more through the repair process.

What we learned was that the 30"-long crack was caused by an attempt to prevent a 3"-long crack. Stone fabricators use a reinforcement technique known as “rodding” to strengthen these thin parts of a countertop. While the countertop is upside down on a work bench, a groove is cut down the center of the strip parallel to the cutout. A reinforcing rod is placed into that groove, and encapsulated with an appropriate resin poured into the groove.

Tests conducted by the Marble Institute of America show that “threaded round steel rod significantly strengthens the stone by 50% in load and 600% in deflection.” All seems very good so far.

But what could have caused the dramatic failure we saw? In order to repair the edge, we had to disassemble the various cracked pieces of stone and rebuild the area. When we did so, we discovered a steel rod, heavily covered with rust, embedded in the granite directly beneath the cracked area. The rod diameter was swollen dramatically, as bulky rust replaced the denser steel. It became apparent that the rod itself was the cause of the problem.

We’ve since done some research that sheds light on this failure. This type of problem is detailed in an article by J.E. Harris in a scientific publication called Advances in Fracture Research. Harris writes that “oxidation is usually accompanied by a net expansion so that when it occurs in a confined space, stresses are generated in the metal component itself or in any surrounding medium such as stone or cement. So much energy is released by oxidation that the stresses generated are of sufficient magnitude to deform or fracture all known materials. This can be very damaging and the process has been termed ‘oxide jacking.’’’

This problem affects everything from nuclear power plants to historic masonry buildings. Oxide jacking led to the collapse of the Mianus River Bridge in Connecticut in 1983, killing three people.

Recommended Reinforcement

The Marble Institute of America published a “Detail of Rodding Reinforcement” in 2005, which recommends that reinforcing rods be made of “stainless steel, mild steel or fiberglass.” In a technical bulletin about rodding, MIA states that “stainless is preferred but not required.” Mild steel appears to be the culprit here.

As long ago as July 18, 1915, The New York Times published an article called “Rust and Mild Steel” about the replacement at that time of wrought iron by mild steel. This article stated: “No sooner had mild steel been in use a short time then it unexpectedly developed great susceptibility to rust.”

The problems associated with mild steel and rust in moist environments have been known for nearly 100 years and yet mild steel is still considered an acceptable reinforcement in areas of a countertop where moisture is likely to be present. The only known advantages of mild steel rod in this application is that it is inexpensive and widely available. We would submit that the potential for oxide jacking is a far more significant disadvantage.

To repair this problem, we first had to eliminate the cause. It became clear that water had seeped between the top surface of the sink and the underside of the granite, eventually wicking into the area of the mild steel rod, initiating rust.

Using a rotary tool and a variety of diamond bits and wheels we dismantled the edge, gaining access to the steel rod to remove it entirely. This procedure also allowed us to adequately clean the surfaces and prepare them for reassembly using a knife-grade epoxy. The result was a repair that was structurally stable, but its appearance was not inconspicuous.

There was minor lippage in the area and the epoxy was a uniform color, highlighting the repair. Grinding and polishing of the area was required to eliminate the lippage.

To address the cosmetic issues with this repair, we used an ultraviolet reactive resin to emulate the patterning and coloration of the granite in the areas where the epoxy was very visible. The advantage to this system is the ability to quickly cure a cosmetic resin fill. Exposure to UV light hardens the resin in less than five minutes, allowing work in the area to resume quickly.

The final steps were to reseal the stone, neatly recaulk the undermount sink and tidy up. The homeowner was advised that the silicone sealant around the sink should be inspected frequently, and reapplied as needed.

Once we could see the cause of the problem, we better understood it and were successful in repairing it. Since then, we have seen and repaired about eight additional examples of the same problem.

Installation of improper reinforcing rods may not be the most common problem with natural stone countertops, but it sometimes results in a catastrophic and dramatic failure that could easily have been prevented. Our recommendation to stone countertop fabricators is simple – use threaded stainless steel rod or fiberglass rod when reinforcing this way. Avoid the use of any reinforcing material subject to rust.

We also recommend that the Marble Institute of America revisit the countertop rodding procedure, and issue a statement strongly discouraging the use of mild steel reinforcing rods, or any other material susceptible to rusting or corrosion.