On the job with Dave Pettigrew
Pettigrew has refined a proprietary mix over the years that allows him complete control over mix color and consistency. He weighs out all ingredients proportionally ? rock, sand, water, powder color, fiber reinforcement and so on ? so that he knows exactly what is in the mix. This allows him to recreate exactly the samples his clients approved. In order to remain consistent, however, he gives special care in the grinding step. "When you hone down the surface you have so much sand you want exposed compared to rock and cement, and you want to keep that ration of sand/cement/rock uniform so it shows the appropriate amount of material," he explains.
When it comes to finishing, Pettigrew uses the technique and products that best fit the job. "I don't use any one type of sealer, I use what works best for the project and the effect the client wants," he explains. A project with a lot of voids or spaces might be best with an epoxy. "Or if they want a natural concrete feel I use a penetrating sealer and beeswax," he explains.
Pettigrew recently completed an outdoor kitchen project that consisted of five cast-in-place concrete elements. The star piece of the system is an elevated horseshoe bar poured around the metal supports that hold up a gazebo. Below that is a main prep area and sink, and behind is another concrete countertop around a custom stainless steel sink with a prep surface. Off to the side is a concrete tabletop near a grill. All slabs were poured 1.5 to 2 inches thick and reinforced with #3 rebar and 6 gauge galvanized sheets with 2-inch squares. "We cut those out and leave about an inch clear around the border and then reinforcement is poured monolithically in the concrete," Pettigrew says.
The project also included a concrete couch with a curved seat and a concrete back rest. The concrete back rest was made of block, and Pettigrew poured the seat and plastered the back rest to give it a nice texture. A matching concrete bench can be found in an outdoor shower.
Another recent project from Pettigrew is a rustic, stone-looking, small precast countertop for a kitchen in an architect's office. It has a mottled, natural stone appearance characteristic of sedimentary rock. Pettigrew used a special technique to achieve this look. After building the mold, he splattered it in an irregular pattern with a baking soda paste. Then he added a cement mix, which included natural limestone in place of the rock and sand. On top of that he hand-packed the concrete. Pettigrew says he often uses this travertine effect on precast columns and fireplace surrounds.