Fake Rocks & Boulders

Making Artificial Rocks
(c) 2009 Some Rights Reserved
by Tom King

A friend of mine makes his living building rocks and designing exhibits for zoos and theme parks. Billy Williamson’s notable work is incredibly lifelike and graces zoos and theme parks all over the country. He kept pestering me to come and help him work on a structure he called a "feed lot for Rose Queens". The structure was a backyard waterfall, stream and swimming pool in the backyard of a local member of Tyler, Texas high society. The waterfall includes a Batcave-style garage underneath the falls where the owner planned to store his Bentley. I finally agreed to join his crew for an afternoon and found myself in welding gloves with an odd bending tool, bending and tying ¼ inch rebar in the Texas summer sun. I was sore for a week. What I learned:


Base

The first part of building artificial rocks is to create the basic shape. You do that by driving rebar into the earth and then using a bending tool to create the skeleton of the rocks and boulders you plan to construct. The vertical rebar, once bent is cross braced by laying horizontal rows of light rebar tide at the point where the bars cross. The tying is tedious, but if you use standard tie wires and a wire tying tool, you can make pretty quick progress. So long as you keep the bars close together and don’t make gaps too large, it’s pretty hard to mess things up. Leave room under the rocks to crawl around under there because you will need to place plastic sheeting behind the rebar.



Backing

Attach heavy gauge plastic sheeting behind the rebar. Use wire ties to pull the plastic up against the rebar to prevent pooling of concrete behind the rebar. Be careful not to rip the plastic. Duct tape can be used to cover tears and holes.

Chicken Wire


Chicken wire makes a perfect framework for the surfaces of artificial rocks. It is shapable, easily cut and quickly attached to the rebar framework. Once all the surface of the structure is covered with chicken wire, go back and tweak the shape a little. Make boulder shapes, cracks, crevices and ledges as you go. Use your creativity. You can even create artificial tree stumps, fallen logs and other natural looking bulky structures.

Concrete

There are two ways of applying the concrete. Lightweight vermiculite or gunite normally used in swimming pools and decks works very well here. The only problem with using a pump, you have to finish the job in one go. For large jobs, this may not leave adequate time to do basic sculpture. To get the proper look for rocks, mix gunite or vermiculite concrete in a wheel barrow and trowel it onto the wire frame. You’ll have to play with the thickness of the mixture to insure it penetrates the wire and rebar without being so thin it is runny. Build up a layer that is at least an inch an a half to 3 inches thick and smoothly covers the rebar and chicken wire. In some places the coating of concrete will be thicker to fill gaps between the chicken wire and rebar. Make sure the rebar below is covered so the rock formation will be strong. Use a flat trowel to smooth the surfaces into the basic rock shape. Do a section as large a section as you can do in half the time you have for the day. Work from the bottom up and apply gently so as not to break through the underlying layer..


Surfacing

When the first layer is partially cured, mix up  a sand aggregate concrete mixture (the kind used for stucco walls and similar surfaces and start at the beginning of the base section you just did. Spread a thin layer of wet finish over the concrete base. You may mix rock colored surface stain in with the mixture or spray coat it on later if you have any special effects in mind. Cover the surfaces of the concrete shapes completely.  Go section by section so your working surface doesn't dry before you can texture it.

Texture

Next, cover the large flat areas with aluminum foil. Do not crumple the foil, but wrinkle it just a little bit and then spread it over the still wet ‘rock’ surfaces and press down firmly as shown in the picture. The foil will give the ‘rock’ surfaces a natural texture.

Cracking


After about 5 minutes, remove the foil and use the edge of the trowel to etch a few cracks into the concrete and to trace seams and layers between separate rock shapes. This takes a steady hand, but don’t make the lines too straight either. Vary depth and width of surface striations to imitate features of natural rock. Lightly brush the rock surface with a paint brush to remove concrete crumbs and create a weathered look. Allow the concrete to set overnight before putting weight on it.

Finish

Once the “rocks” are set and dried, brush or spray on stain. Even if you applied stain to the finish itself, you should add contrasting colors to accent cracks, seams and shadows. It requires an artist’s eye and a lot of practice as you can see from these shots of Billy Williamson’s finished projects. It’s an art form and if you ever get a chance to work with someone like Billy who understands it, take the job! Mimicking Mother Nature is a whole bunch of fun!


This is one of the exhibits at Tiger Creek Wildlife Refuge that Billy designed and help build (below).  Tiger Creek is home to a large collection of rescued tigers, tiger cubs and other big cats located just north of Tyler, Texas.  Tiger Creek is a not for profit organization providing rescue services and shelter care for tigers and big cats.

These tigers below are enjoying the summer sun sprawled on the waterfalls and rocks built by Billy and the volunteer crew and Tiger Creek staff.

 These guys play rough, but the rock formations can handle the pounding.

 This next exhibit was built for a Tennessee zoo by, also by Billy Williamson.  The black bear in the exhibit enjoys the waterfall and stream in his new home.

This fat bear is having a little soak.  Not a single rock here is real.  All were sculpted by hand using the method described above as was the creek below in a chimpanzee exhibit.

Note, there is not a single loose item in the picture below.  Chimpanzees love to throw rocks and loose objects.  Billy's knowledge of chimp behavior led to this design in which everything in the river is part of a single piece of concrete, sculpted and staied to look like an ordinary stream full of rocks and deadfall trees, but without the hazard to keepers and visitors of having a loose rock heaved at you by a mischievous chimp.

Photos (c) 2009 by Tom King, Tiger Creek Wildlife Refuge and Billy Williamson (All Rights Reserved)