Building a custom patio
I live and work in the mountains outside Denver, Colorado. The terrain is steep and rocky. Excavation usually requires the use of explosives, so the homes are custom; each designed to fit the property. Here every project comes with its own set of unique challenges.
Asked for designing and building a custom patio, I met with the owners who led me onto a long wood deck. Adjacent to the deck was a slopping, bowl shaped area, covered in high grass, and littered with large stones. Steps led down to a 6-foot square landing made from two 3-foot by 3-foot stone slabs, each approximately 2½ inches thick.
The owners liked the color, texture, and mass of the existing landing and wanted the new patio to match the stone as closely as possible. The area where the patio was to be built was accessible only by a narrow path, so I wouldn’t be able to bring in any equipment; everything would have to be done by hand.
The first step was to establish the perimeter of the new patio. The area was an organic shape, bordered on one side by the existing deck and loosely defined by a crescent shaped hill on the other. To establish the curved line for the outer edge of the patio I used a garden hose, setting stakes at 4-foot on center along the curve. Once I had the footprint of the patio established, I pulled measurements from the existing deck to each stake and graphed the patio on paper, so I could estimate materials.
Using dry-lines, a spirit line level and plumb bob, I determined the area sloped downward 30-inches over 39-feet. I would have to excavate 15-inches from the upper end, and use the material as fill for the lower.
I had to “grub” the area, removing organic materials from the soil so that it could be used as fill. I worked the soil with a pick, landscaping axe and steel rake until I could separate the root mat left behind by the grass.
I needed a retaining wall at the low end. I wanted it to look like a natural rock formation, so instead of forming it from concrete, I built it with stones from the property. I pried large stones loose using a 6-foot steel bar, rigged a sled from plywood and rope, and dragged the biggest rocks I could down to the worksite, where I set them into position to form the retaining wall.
Once I had the retaining wall built and the area cleared down to bare soil, I set up a grid of string lines to establish where to cut and fill.
The ground contained nearly as much rock as soil, with stones ranging from 2 to 12 inches in diameter. In order to get good compaction, I had to remove the rocks. I did this using a homemade sifter similar to what you might see on an archeological dig. I built a 36-inch square frame from 2x4s and covered the bottom with ½-inch wire mesh. I placed the screen on top of a wheelbarrow, as I dug I’d throw shovels full of dirt and rock onto the screen. The dirt would fall through, and rock would be left behind.
The soil at the site was decomposed granite with a consistency between course sand and fine gravel. Normally I’d put down a layer of sand as a base for the concrete, but with the decomposed granite, it wasn’t necessary.
I used the stone landing as the starting point for the layout of my 3-foot square concrete pavers. The first line parallel to the deck was set to align with the outside edge of the landing and the first perpendicular line was set to the center of the landing.
I ripped 2x lumber into 1½- by 1¾-inch boards, using 16-foot material for the forms running parallel to the existing deck. I predrilled ½-inch holes at 3-foot on center through the 1¾-inch face of each piece. I cut 3-foot forms for use along the perpendicular lines. Using a countersink bit, I predrilled each end to accept a wood screw for attaching the 3-foot board to the full-length forms.
I set my first form parallel to the deck and using 12-inch spikes through the predrilled holes, secured the form to the ground. Then pulling measurements from my pre-established centerline I marked the parallel form to create 3-foot spaces between the short perpendicular form boards. I screwed the precut, predrilled boards to the long form. Then I set the next long form and continued to build out my grid. I periodically checked individual pavers to insure my layout was square. I made sure the spikes and screws where driven flush with the form to create a smooth surface for screeding the concrete. Where the formwork intersected the curved rock retaining wall and hillside, I cut forms to fit.
I brought in a small concrete mixer after determining the patio would be 650-square foot, requiring 3-cubic yards of concrete. Each 36-inch square paver required 1.12-cubic feet of material. The concrete was mixed in 2-bag batches, each weighing about 176-pounds, loaded into a wheel barrel and rolled to the patio. In all I moved more than 11,000-pounds of concrete for the job.
Using the existing stone slab as my color pallet, I picked three complimentary shades of New Look Cement Color synthetic mineral oxide powder. I set my dyes near the mixer, and alternating between colors, added a cup of dye to each 2-bag batch of concrete. After I poured the concrete into the wheelbarrow, I was careful to wash the remaining dye out of the mixer.
Each batch filled one paver, with a small amount left over. This was pushed into one corner of the next form. When the form was filled with a different batch and finished, the effect was a more natural blending of the three colors.
In order to have the finish surface more closely match the stone pavers, we purposely left slight arched trowel lines in the concrete. Once the concrete was placed, I covered the slab with plastic sheeting and let it cure 72 hours.
To strip the forms, I used a wrecking bar to pull the 12-inch spikes from the long form boards, and an impact driver to remove the screws that secured the 3-foot forms. Once the fasteners were removed, the forms came out with relative ease. Then we filled the gap between the pavers with sand.
– By Michael Davis, Framing Square Construction, Conifer, Colorado