Q&A / 

Decorative Patio Stones

DEAR TIM: I was on vacation before Christmas visiting relatives in southern California. I love outdoor plants so we visited a place called Huntington Gardens in Pasadena. There I saw the most unusual patio and sidewalk paving. Never before had I seen such beauty and thought it was fake. Different small stones that were different colors and shapes were combined to create a gorgeous pattern. How can I duplicate this or at least get close to what I saw? I intend to do this myself. What needs to be done to ensure all the hard work doesn’t fall apart, crack or otherwise deteriorate. I live where we get freezing weather unlike sunny southern California. Mary S., St. Paul, MN

DEAR MARY: I’ve built lots of patios in my life and many years ago built a medium-sized decorative stone-encrusted fishpond for my wife at our second home. What’s more, I’ve walked on that patio you saw in Pasadena. In fact, I photographed it for my own records because it was so unique. I believe I know exactly how the master stone masons built that patio and the connecting sidewalks. While there I knelt down and studied it.

Here’s just a small section of a massive patio and sidewalks constructed with decorative stones at the Huntington Gardens in Pasadena, CA. © 2016 Tim Carter Builder

If you intend to duplicate exactly what you saw, you’re going to spend quite a bit of money to make the curved pieces of stone that create the border around the rounded white stones you saw. I can only imagine what the price of that might be. If it’s out of your budget, think about going with a pattern that can be done with straight pieces of stone you cut to fit. I agree that the curved border and curved pieces of border that connected the emblems are part of the overall beauty of what we saw.

You’ll also have to source all of the materials you saw in that patio. Besides the curved stone border sections, you just need to locate the smooth white stones and the thin gray rock that was installed on edge in between the white pebble emblems.

It could be very difficult to source these near your home and you may have to substitute other material that looks similar. In fact, you may discover that you can find other stone that has colors that look even better than what you saw. Be sure the stone retailer can prove to you that the stone you choose can withstand freezing temperatures in a horizontal position in the ground. Not all stone can survive these conditions.

The first thing you need to do is create a scale drawing of what you have in mind. This drawing will help you estimate the number of curved pieces of cut stone for the borders. Be sure you order no less than 20 percent more than you think you’ll need. Some may get broken in transit and you simply can’t afford to run short of this special material.

Based on what I saw at that patio and without doing any forensic snooping which would be very unprofessional since it’s not my patio, I estimate the finished patio covering was about 1.5 inches thick. Both the curved border pieces and the thin stone on edge would be the same height. This makes it somewhat simple to install most of the finished stone.

Beneath the decorative stone you and I saw I’m sure there’s a poured concrete sub-base patio. This is how I built all of my past decorative brick patios. The brick I used happened to be 1.5 inches thick and I set them in about a half inch of cement mortar.

I’d pour the concrete slab 5 inches thick and I’d have one-half-inch steel reinforcing bars in the middle of the concrete in a grid pattern much like common graph paper. The steel should be no more than 2 feet on center in both directions. This steel prevents the concrete from developing wide cracks and it helps keep the concrete all in the same plane over time. It’s important the concrete is poured on well drained compacted soil.

The concrete slab needs to be finished with a sandy or broom-finish and it must be in the same plane. Be sure it has some tilt to it so water drains off the slab and doesn’t puddle. Any water that falls on the patio needs to be able to drain away.

Because you live where it freezes, I’d design your patio so it drains water away from the underside of the decorative stone. I’d want the decorative stone to sit on top of small rounded pea gravel that’s about 1 inch thick on top of the concrete. Water that falls on the patio will pass down to the pea gravel stone and then gravity will pull it to the sides of the patio. Be sure the low side of the patio allows this water to drain away through a buried pipe system on the outside edge of the patio. This prevents water from collecting under the decorative stone which will freeze in winter and cause havoc.

The center of the emblems would be installed using pigmented Portland cement mortar and fine sand. I’m sure the masons at Huntington Gardens used pure silica sand and white Portland cement based on my inspection. Silica sand is a great material because it’s a uniform color and quartz is such a durable mineral. You can easily get bags of silica sand where you live.

The rounded stone were set in fresh mortar to hold them in place. I’d make a strong mix of 2.5 parts sand to 1 part Portland cement. It will require some practice to get the mortar so it lays flat in between each rounded stone. I’m sure you’ll have to use a small stick or tool to tap the wet mortar to get it to the required height.

To achieve perfect results, I’d build a small patio first. You can test out your skills there to ensure the materials will all work well together. Don’t underestimate what water will do to the patio system in the winter months. You must engineer a way for rain water to rapidly flow off the top of the decorative stone and from beneath them.

Be sure to purchase some excellent knee pads as you’ll need them. You’ll spend countless hours on your knees building this patio, but it will be worth it.

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