• In-house control: While some still argue about which process is best  wet or dry shotcrete  experts agree that either will yield a great product if done correctly.  It really comes down to personal preference, cost and the quality of the local labor pool and ready-mix plants. Some builders and subcontractors prefer to have complete control over the quality of the mix, as opposed to relying on ready-mix plants. Gunite, or dry shotcrete, is the choice for them.

    Credit: SOUTH SHORE GUNITE POOL & SPA

    In-house control: While some still argue about which process is best — wet or dry shotcrete — experts agree that either will yield a great product if done correctly. It really comes down to personal preference, cost and the quality of the local labor pool and ready-mix plants. Some builders and subcontractors prefer to have complete control over the quality of the mix, as opposed to relying on ready-mix plants. Gunite, or dry shotcrete, is the choice for them.
  • Westward ho! Wet-mix shotcrete was long considered a bastion of the Northeast. But these days, the process is moving west, with Southern California, Phoenix and large swaths of the Pacific Northwest adopting it. Similarly, gunite, or dry-mix shotcrete, has seen its popularity increase on the East Coast.

    Credit: SOUTH SHORE GUNITE POOL & SPA

    Westward ho! Wet-mix shotcrete was long considered a bastion of the Northeast. But these days, the process is moving west, with Southern California, Phoenix and large swaths of the Pacific Northwest adopting it. Similarly, gunite, or dry-mix shotcrete, has seen its popularity increase on the East Coast.

Which is better — gunite or shotcrete?

It’s a conversation that continues more than 80 years after the process of pneumatically applying concrete was first used on swimming pools.

The conversation isn’t always so calm, as builder Tony Caciolo found out when he added a pool operation to his home building company about five years ago.

“I’ve been to all the classes with all the experts out there, and they’re six of one, half dozen of the other,” says Caciolo, president of Monogram Custom Homes and Pools in Coopersburg, Pa. “If you put 100 guys in a room, you can be sure half will argue about gunite and the other half will argue about shotcrete. I’ve been in seminars where people talk until they’re blue in the face arguing pros and cons.”

Unfortunately, this debate can surface during sales presentations, where builders sometimes badmouth the other process. “I know a salesman here who bashes the gunite process, even though that’s what he sold at his last job,” says Jim Sankey, president of James Sankey & Associates in Warminster, Pa.

Here, we look at the pros and cons of each process, along with some regional changes that have occurred.

Back and forth

Both sides of this argument generally take pride in what they do.

Guniters will remind you that New York’s Grand Central Station and Holland Tunnel were made with the gunite process, while shotcrete proponents point to new portions of the Weehawken Tunnel and the World Trade Center.

But the truth is probably represented more by the experience of Bill Drakeley, who shotcretes pools but also performs both processes for infrastructural construction. “It’s the type of job, it’s the requirements of the job and then the availability of the materials,” says the owner of Drakeley Pool Co. in Bethlehem, Conn.

Drakeley recently worked on a subway tunnel in New York, training and supervising 147 union workers using both gunite and shotcrete. To cover the 1 million square feet of surface, his crews shot 46,000 cubic feet of wet mix and 11,000 of dry.

“Most of our shooting was high volume, and we had to keep a good pace going,” he says. “The ideal method was wet [when] we could get the material there easily, versus some of the molding or some of the ring steel shooting where we had to use dry [because] we had to start and stop. … Getting a pump truck in certain parts of the tunnel was very, very difficult, so dry came in handy. So it’s the application.”

For the most part, professionals will admit that either process will yield a high-quality product if applied correctly.

“Shotcrete is a process, it’s not a product,” Drakeley says. “Hardened, in place concrete, whether dry [mix] or wet [mix], are equally as good,” he explains. “Once it comes out of the gun and goes onto the surface, your performance should be the same. Your technology is the same, your intentions, your design are all the same.”

It seems to be a matter of which method makes an individual builder or applicator feel more confident, the reputation in a given area and the cost and quality of local plants and workers.

But gunite, in particular, has taken a beating because so much of the quality relies on the workers, who must create the proper mix on-site.

This bad rap has some historic explanation, says Drakeley, who also is a member of the American Concrete Institute’s 506 shotcreting committee main body. “The reason the ACI and specifying engineers kind of look down on pool people is the absolute horror stories that have come out about pool construction over the last 30 years,” he says. “Most of those horror stories are from the dry side.”

Others agree.

When researching whether to incorporate a shotcrete or gunite operation into his Atlanta-area plastering business, Shawn Still found that gunite had a bad reputation.

“There are a lot of variables for quality control,” says the general manager of Olympic Pool Plastering in the Greater Atlanta area. “If done right it’s a great product. But here we’d find you may have a section of floor that’s 5,000 psi and then another section that’s 1,800 psi, whereas with shotcrete, it’s going to be a more consistent psi throughout the entire shell.”

Regional shifts

But that reputation doesn’t hold in other areas. Because of this, the regional lines are beginning to blur as far as who uses shotcrete and who uses gunite. It used to be conventional wisdom that the Eastern part of the country used shotcrete, while the West went with gunite.

Pennsylvania’s Lehigh Valley is the birthplace of gunite. But, ironically, it traditionally used wet-mix for pools. But when Caciolo did research before opening his operation, he found that was no longer the case. He cites at least one local builder who used to use wet mix and had to fix serious failures. “He switched over to gunite and hasn’t had a problem since,” Caciolo says. “Just about every builder in our area has switched to dry mix gunite.”

He doesn’t know if the problem is the skill level of the applicators or the ability of local batch plants to make timely deliveries of the concrete in such a rural location. “But I can tell you that since the guys switched to gunite, those cracking problems have gone away,” Caciolo says.

Where the Northeast long has been considered a home to shotcrete, the Tri-State area — the parts of New York, New Jersey and Connecticut surrounding New York City — has moved more toward gunite in about the past five years, says David Reeves, president of GSI Pool Finishes in Philadelphia. “It’s 10-to-1 gunite,” he says.

Conversely, parts of the West, which used to be gunite territory, have begun switching to shotcrete. The process has especially gained popularity in Southern California and the Phoenix metro area. Builders and applicators cite the ability to rely on batch plants to maintain the quality, but they also made the move due to price. Contractors report that a gunite operation costs an average of 30 percent more to start up due to equipment costs. Because batch plants deliver the material, the shotcrete process requires fewer trucks, less clean-up, no materials storage and, some say, fewer crews (although they still should meet ACI standards for staffing a job).

More alike than different

There are some things with which neither gunite nor shotcrete proponents will argue.

For instance, guniting requires a significantly higher start-up investment than shotcrete. But it also is more forgiving timewise than shotcrete. In order to maintain its integrity, a truck containing wet-mix concrete for the shotcreting process should be emptied within 90 minutes of the material being dispatched. On the other hand, dry-mix concrete for the guniting process is mixed at the nozzle on an as-needed basis, allowing crews to stop and start on a project and really take their time on detail work.

But some builders have found a workaround on that issue. For instance, South Shore Gunite Pools & Spas has purchased a portable mixer, which will create the wet-mix concrete on site. “We mix our wet on-site, so we only mix as much as we can use at the specific time, then we stop and catch up,” says Robert Guarino, president of the Chelmsford, Mass. firm.

But there are some aspects of this discussion on which the sides differ. For instance, some say gunite is better for jobs that require stopping overnight or for a length of time. This perception can be attributed in part to the time crunch that goes along with the shotcrete process, but it also comes from the fact that wet-mix concrete has more water, and therefore, is more prone to shrinkage cracking. This leads some to state that, with the surface cracks, the final product is not sound if not shot monolithically.

That perception is false, Drakeley says. He contends that a shotcrete job can be stopped for up to a year then picked up again, with the right surface preparation, which involves the same routine that a gunite crew must go through to shoot onto previously shot concrete. “There are no expansion joints, no bonding agents needed, no cold joints. Preparation is exactly the same for dry or wet: You get your joint prepped properly, open the pores in a three-dimensional bond plane. You get it in something we call an SSD condition — saturated surface dry — and you spray your mix design into those pores, and it makes a chemical as well as physical bond.”

In fact, it’s rare for his crews to shoot an entire vanishing-edge wall in one day.

Some also say the gunite process is more suitable for work that requires precision, such as vanishing-edge and perimeter-overflow weirs that must be almost perfectly level and smooth to facilitate even flow. The finer aggregate needed for dry-mix concrete to be mixed at the nozzle makes it easier to cut a perfectly flat surface with little to no texture, some say.

But Still says his crews can cut just as flat of a surface as his guniting counterparts. The trick? Order a small-aggregate mix. This isn’t available in every area, but it’s a requirement for Still.

“The size of the stone makes a huge difference,” he says. “No. 89 stone is what you have to use for tighter radiuses. [It’s] a 3/8-inch stone ... a tiny little pebble. They compact really well. If a [vendor] says they don’t have it, we usually won’t use them. I’m not going to be on the hook for an ugly shell because of the type of concrete that they provided. If all you have is No. 7, which is half-inch stone, then it’s way too big. You can’t do anything with that.”

Guarino comes at it from another position. He shoots both wet and dry but specifically prefers wet for vanishing edges. He finds it easier to get the wet mix to completely encapsulate the larger, often doubled-up rebar found in these features.

“The dry mix wants to build up on the face of the rod,” he says. “And sometimes you’ll generate voids behind the rods as the wall’s being constructed. It doesn’t flow very well on its own, so you have to be very aggressive with your nozzlemen and your nozzle techniques ...”

Another perception says that shotcrete is automatically more reliable, since the batch plant can certify the concrete’s strength. Successful gunite, on the other hand, relies on crews having the integrity to resist adding too much water, and to use the right amount of cement, rather than going heavy on the less expensive sand.

But builders such as Caciolo and Sankey like being in charge of the product’s strength and integrity. “[With shotcrete] you don’t get to see what’s happening — you don’t get to see the mix,” Caciolo says. “Whereas when we’re shooting gunite, we can see right then and there what the mix is like. If it’s too wet, they turn it down; if it’s too dry, they turn up the water.”

This also means that he makes sure to be on the site during the guniting phase to supervise, he adds.

Besides, gunite proponents say, there are ways to cheat at shotcrete, too. Shotcreters can add water as surely as guniters, Reeves says. And not all plants provide a stellar warranty. “Here, it’s certified on the truck. Then once it leaves the truck, there’s no certification, no warranty.”

Additionally, you have to be confident that the scales at the plant are always set accurately. In Reeves’ experience, the same plant fulfilling the same order might fill his hopper with 6,000 pounds of concrete one day, and 8,000 the next, because the scales are off.

“You can cheat on anything,” Sankey says. “It’s all in the quality and the pride.”

For some professionals, the term gunite sounds like fingernails on a chalkboard.

Since the mid-1960s, the American Shotcrete Association refers to both forms of pneumatically applied concrete as shotcrete, with one called wet-mix and the other dry-mix. However, the pool and spa industry continues to refer to them colloquially as gunite (dry mix) and shotcrete (wet mix). The term “gunite” came from the Cement Gun Co., which acquired rights to the technology just over 100 years ago and now is owned by German manufacturer Putzmeister. The wet-mix process came in the 1950s. The ASA veers away from the term gunite because it was once a trade name.

Because the trademark no longer exists, this article continues to refer to the dry-mix process as gunite in light of the industry’s familiarity with this term.

However, because shotcrete is the term approved by the American Concrete Institute, the word will appear in legal documents and proceedings, whether it is referring to wet- or dry-mix.

More than rhetoric

For some professionals, the term gunite sounds like fingernails on a chalkboard.

Since the mid-1960s, the American Shotcrete Association refers to both forms of pneumatically applied concrete as shotcrete, with one called wet-mix and the other dry-mix. However, the pool and spa industry continues to refer to them colloquially as gunite (dry mix) and shotcrete (wet mix). The term “gunite” came from the Cement Gun Co., which acquired rights to the technology just over 100 years ago and now is owned by German manufacturer Putzmeister. The wet-mix process came in the 1950s. The ASA veers away from the term gunite because it was once a trade name.

Because the trademark no longer exists, this article continues to refer to the dry-mix process as gunite in light of the industry’s familiarity with this term.

However, because shotcrete is the term approved by the American Concrete Institute, the word will appear in legal documents and proceedings, whether it is referring to wet- or dry-mix.