Nature appears random, yet that’s far from the case. Rocks change color and form for particular reasons, with aging and staining playing a role along with pressure from neighboring stones.
Experts like to say that every rock formation tells a story and to ensure that the tale rings true, designers should plan projects well in advance from the perspectives of aesthetics and construction alike. A detailed mapping system aids in client communication as well as helps maintain adherence to the design on the part of crews.
The design
Development of the concept begins with research. The designer should ascertain the clients’ needs as specifically as possible, including exactly what type of rock is to be formed.
It’s helpful to ask customers to select between rounded or angular shapes, and gray or brown tones. Color samples and photos can be effective, but some in the field prefer to show a piece of actual rock, perhaps from a local stone yard.
Installers can then analyze the sample specimen to replicate it. For example, if a given rock contains 10 percent gold, 1 percent red and 1 percent cocoa, those proportions can be expanded across a 1,000- or 2,000-square-foot project.
The client may want to replicate rocks from specific regions of the world, or imitate local varieties for an indigenous effect.
To prepare, some rock sculptors review photos from a variety of angles and distances. Images taken from farther away showcase the overall shape of formations, while close-ups indicate cracking patterns and subtleties such as color, lichens, algae growth and mineral stain.
Once a rock’s characteristics have been decided, it’s recommended that they be carefully documented so that the client, designers and crews are all working with the same expectations.
Using a schematic to decide where larger rocks and special features will sit is helpful in the planning of waterfalls, grottos, sitting areas and larger specimens. Establish the basic shapes, colors and cracking patterns of all rock. Then have the clients approve it.
A three-dimensional model leaves even less room for misinterpretation and can eliminate disappointments and possible lawsuits. People tend to understand a full rendering infinitely better than lines on a paper or screen.
If constructing a model, be sure to build to a scale of 1/2-inch or more because less than that makes it too cumbersome to accurately measure. Using these guidelines allows crews to work without constant supervision, and the finished product generally falls within a foot of the original plans.
It’s also important to remember that the model is where the story gets told. Why did a rock fall to create a natural bench? Where did cracks intersect, causing a chunk of rock to split? The model should address all of the variables, including basic shapes, the direction of strata in sedimentary varieties, and where major rifts, cracks and veins occur.
To further prepare the installers or carvers, some designers create a manual for the rock artists. It contains photos, dimensions and concrete mixes to be used.
To maintain consistency, color a portion of the rock at the start of the project, so installers can imitate it. Then ask workers to photograph their progress at least every other day, so a designer can inspect it.
Finally, create a pool wall that conforms to the rock. Most formations don’t follow a straight line; instead, the mass will generally bend, creating canyons and peninsulas. To mimic this effect with a raised bond beam, builders must design a wall that outlines this motion.
However, contractors can’t construct a straight wall and simply hang rock on it, especially in earthquake-prone regions. California earthquake tolerances only allow up to 18 inches of material to cantilever off the wall, which would prevent dramatic shaping.
The structure
The rock may be artificial, but the consequences of improper engineering and construction are all too real. That’s why many government entities are paying more attention to man-made rock structures, making sure that they adhere to concrete codes.
No universal regulations exist for artificial rock, but in many ways, the structures are akin to building a pool. They impose dead weight, are affected by soil conditions and may support people or earth.
While planning the project, it’s crucial to address engineering concerns and, if the rock will impose an extraordinary load, then seek help from an engineer.
Grottos, for example, place tons of weight on the ground as well as overhead. Retaining walls also must support a massive amount of soil. Consult with an engineer for both of these structures.
Once on site, start with a strong foundation. The ground’s surface is always subject to small movements, settling or raising, depending on the soil conditions. Thus, artificial rock needs a footing to properly anchor it in the soil.
A footing also prevents moisture from seeping underneath the rock and eroding, creating a void between it and the earth.
Some builders dowel their rockwork in the ground with rebar, but that’s not sufficient.
The rock is sitting right on the surface and can settle, which in turn, can cause cracks or impose weight that pulls on the pool.
Before installing the rockwork, make sure you moisten the footing because this will help ensure proper bonding.
It’s also important to remember that, like everything else, artificial rock is subject to gravity. If installing it on a slope, be sure to cut a flat terrace for the work, and consider pouring a slab because this would stabilize the rock even more.
Finally, build the rock itself for strength since, if not properly constructed, it can begin to deteriorate. There have even been cases where people have fallen through due to shoddy construction.
Start with a framework made from an appropriate reinforcement material such as rebar. This will make the project structurally sound.
Next, ensure proper encasement of the steel. Nos. 3 and 4 bars require 11/2- to 2 inches of concrete on either side, for a total thickness of approximately 4 inches. This is true regardless of the application.
On hollow rocks, this can pose a challenge. If using shotcrete, designers will need to plan for a backing against which to shoot in order to avoid filling in the whole piece. Make sure the backing is sturdy enough to remain motionless while the concrete is shot against it.
Many builders use burlap, which is not recommended because its flexibility creates a lot of movement and vibration during guniting or shotcreting. This prevents good encasement of the reinforcement.
Instead, use a well-secured, expanded metal lath or wire mesh. Some installers also shoot against foam. In addition, use dobies — those small concrete blocks on pools that separate the earth from the rebar — to prop the cage off the backing so that concrete goes all around it.
When attaching the framework to a wall or footing, insert epoxy in all the dowels rather than merely pounding the rebar into the hole with a hammer.
A No. 3 rebar is designed to carry 2,000 pounds of tension. Thus, if 2,000 pounds of tension is placed on it, the rebar will come out.
Also, remember to shoot with a concrete of the correct strength. Some codes require as little as 2,500 psi, but other officials and experts say it should be 4,000 to 4,500 psi.
Pool & Spa News would like to thank the following people for their invaluable contributions to this story:
Neil O. Anderson, president, Neil O. Anderson & Associates, Lodi, Calif.
Philip diGiacomo, founder, diGiacomo Inc., Denver
William Ehler, owner, Natural Design Swimming Holes, Auburn, Calif.
Rodger Embury, founder, Rock & Water Creations, Fillmore, Calif.
Ron Lacher, president, Pool Engineering Inc., Anaheim, Calif.
David L. Manwarren, president, David L. Manwarren Corp., Rancho Cucamonga, Calif.
Diane Minks, freelance rock artist, New York
Bruce Riley, managing director, RicoRock Inc., Orlando, Fla.
Matt Wilson, president, Outdoor-Republic, Pleasanton, Calif.
