A flat rod prior to being imbedded in slot.
The wet epoxy is being poured into the slot
Top: The rod is being set into wet epoxy already poured in the slot.
Bottom: The rod is being “seated” in epoxy.
Pictured above is a rodding failure. The fabricator failed to remove the dust after cutting slots and used polyester to set the rods.
As a new or future fabricator of natural stone, one thing that you have probably heard, seen or read about is a technique known as rodding. What is rodding and when is it warranted?
What’s It All About?
Rodding is not rocket science. Rodding, in my opinion, is simple and cheap insurance for you, the fabricator. Technically, rodding is the act of strengthening a piece of stone by the insertion or imbedding of a reinforcing rod with epoxy glue. If you have ever been stuck in traffic due to road construction and seen steel rebar being laid down ahead of a concrete pour, that’s the same thing. When I explain rodding to my customers, I use the “rebar in the concrete” analogy, and the “scared deer in the headlights” look on their faces almost always changes to the old “Oh . . . I get it” look.
Traditional rodding techniques employ cutting a slot in the back side of a piece of stone along the length of the piece about 1 1/2 in. back from the front edge and 1 in. in from the back edge. The slot is usually ⅜ in. deep in 2-cm stone, and ½ to ⅝ in. deep in 3-cm stones. The slot will usually be ⅛ in. wider than the width of the rodding stock. For example, ¼ in. round stainless steel stock usually has a ⅜ in. wide slot cut in the back side of the slab.
Once the slot has been cut, the slot is then vacuumed out to evacuate all dust particles. The rod material is then “roughed up” with a coarse grit stone to give it more ability to hold the glue that will be used to “grab” to the roughened metal. This also removes any rust if the rod material is cold steel. Fiberglass flat rods can also be used and require a bit less preparation than steel. Aluminum, however, should NOT be used because it has a different rate of expansion than natural stone causing cracking of the stone in the right conditions. (I have seen this a few times in the last couple of years, so take my advice: Rodding, good. Aluminum, bad.) The steel or fiberglass rods are cut to size so they will fit into each slot without having to be forced in. They are then removed to await final imbedding into the back side of the piece.
Next, epoxy glue is mixed up in the proper ratio of hardener to resin. Each piece should be completely dry before this next step. The rods are placed back into the appropriate slots so they are below or flush with the underside surface of the stone after the epoxy has been poured into each slot. The rods are then pushed down into their appropriate slots, and the excess epoxy is scraped off while the glue is still “plastic.” After, the pieces are set aside to dry, undisturbed, for about four to six hours depending on the ambient temperature of your shop.
Once the glue is dry, the back side of each piece is quickly ground down with a coarse steel cup wheel to remove any latent amounts of glue that did not get scraped off when the glue was wet. Once this step is completed, the piece is now considered to be “rodded.” After rodding, the piece will be stronger and more resistant to flexural breakage due to the inclusion of the steel rods in the back of the stone. Again, you can look at this as cheap insurance — especially if you have lots of bumpy roads to travel over in order to get your piece to its final destination.
TO ROD OR NOT TO ROD
This rodding technique should be performed on any piece of stone that has a potential to break — from the moment it comes off of the saw until it gets installed. Some fabricators rod all of their pieces regardless of size. Other fabricators limit the pieces they rod to anything that will have a cutout done, either at the shop or on-site, prior to final installation. Pieces that are good candidates for having rods imbedded in them are pieces that have a cooktop cutout, all undermount sinks, self-rimming sinks if the cutouts are done before the final installation, extra-large pieces like islands, pieces with overhangs, and especially pieces that already have fissures in them like gneisses and schists. Any stone that is extra brittle and has visible fissures in it should be rodded.
Rodding is an easy and cheap way of making a weaker piece of stone stronger and should be used any time you have a natural stone that could break during transit from your shop to the jobsite. Here’s an added bonus: Your customer will reap the benefits of having their pieces rodded since the rods will stay in the stone forever, helping to increase a piece’s ability to resist breakage.
Just because a piece is rodded does not mean it will never break. Remember to remind your customers that the rods are there to help strengthen the piece, but it could still fracture due to abuse.