Finishing Touches on a Flagstone Patio

See the second part of a flagstone patio installation where stones and sands are added to the design. 

Come to find, a new patio is the ULTIMATE in summertime happiness, and I’m not just saying that, this thing is awesome. After we laid the flagstones over the course of last week, I was pretty excited to finish the project, and there wasn’t a lot left to do: Just laying in some extra detail, and filling all of the cracks with polymeric sand.

This special detail came in the form of beach pebbles that we’ve accumulated over time. The smooth, colorful, and plentiful little rocks added special detail, and also filled in the bigger cracks where we weren’t able to get the flagstones close together. The finished patio is really beautiful, and I’m so proud of it.

If you’re working with big irregular flagstones and not bringing a stone saw into the mix, you’re bound to have a few big gaps. We considered this upfront, and therefore spent an hour on the beach collecting some little rocks that would find a new home in the backyard.

The pebbles themselves, while small and of varying colors, looked really great in contrast to the massive flagstones. I spent an afternoon on the ground with a rubber mallet tapping them lengthwise to wedge them in between spaces in the rocks, far enough down to feel well-anchored in the sand, and also flush with the top of the flagstone so they wouldn’t be inclined to trip anyone.

Most of our gaps were small – one to two inches – which we knew our high performance Techniseal Polymeric Sand could easily accomodate. But there were also some big gaps. As we worked to lay the flagstones, we had worked hard to make sure these big gaps were dispursed all around the patio, knowing that we wanted to use the pebbles, and we wanted them to be used in a similar way around the entire space. It might have looked silly if all of the flagstones lined up perfectly on the left, and there were tons of big gaps on the right, you know what I mean?

Here is a bigger gap visual:

Once that same gap was filled in tightly with various pebbles, it looked like this:

And when all of the cracks had been sufficiently filled, the flagstone patio looked like this:

To be honest, we’re not sure how well these pebbles will hold in place, even after being coated with Polymeric Sand, but it was a risk we wanted to take. When you’re a professional DIY-er, you accept that what you’re doing is often an experiment.

We weren’t able to find any tutorials strongly advising for or against using pebbles as a detail, but I’ve seen it being done more and more often in landscaping design, so I figured it was worth a try. If it comes down to it, we will be able to remove them and fill the entire crack with polymeric sand. And from what we understand, it’s not as though the polymeric is going to keep even the flagstones themselves from shifting, so anything could happen. We made the best underlayment that we could, but nothing’s guaranteed to be permanently locked in place, so I’ll hold my breath during the winter months and see how the patio looks come spring.

I’ll be specifically honed in to see how the pebbles hold around the edge. I used the biggest of the stones here in an effort to keep them really anchored, embedding them upwards of 6″ deep into the ground.

We used a bunch of pebbles, but tried not to go into pebble-overload mode either. They were used sparingly in small cracks (spaces one to two inches wide), but not in every small space.

The pebbles look tiny in comparison to the flagstone rocks, but don’t be fooled – many are the size of my fist (and bigger!). And just to keep showing you pictures because I love it so much, my favorite little grouping looked like this:

Once the rocks were set, we cleared the surface of any remaining leaves and twigs that had fallen on the stones with Pete’s leaf blower, and then began to fill the cracks with polymeric sand. We bought four bags of the Techniseal Polymeric Sand (HP) because we were dealing with wide paver joints and also high humidity. I chose the Granite Gray color of sand, although I was told that the tan color is also popular for flagstones. True story: We only used two bags of polymeric sand, so I was able to return the other two and save $75. (I assume they over-estimate these kind of things so we don’t have to make another trip back to the store for more, but also, the stones took up a fair chunk of the space we needed to fill!)

To focus our application efforts, we made a little hole in the top corner of the bag, and treated it like a baker might treat a frosting piping bag; the sand poured out in a very controllable/minimally dusty fashion.

While I poured, Pete followed behind with a small hand brush from the shed, and made sure that all cracks were filled evenly. He also made certain that there was no sand sitting on top of the stones, because anything that sat compacted in the creases of the stones was bound to harden on them (polymeric sand hardens in a cement-like way, which is great for keeping weeds out of your patio area, but not the kind of thing you want to be inhaling or spreading all over your stones like beach sand).

We used the leaf blower one last time before wetting the surface, but lightly so that we didn’t inadvertently blow the sand from between the stones. By focusing on aiming at the big rock surfaces, we didn’t do any damage. Before the polymeric sand was set, it looked like this. Note how much of the stones ended up being embedded in the sand, and how little was really exposed:

Wetting the polymeric sand is the big nervewracking part of the whole project; once it’s wet, it’s gonna set. Using shower mode on our hose sprayer, I lightly coated the surface, working from the bottom of the slope up towards the part of the patio that was graded higher. I only wet the area for about 30-45 seconds, but then followed back up with two additional light spray downs to make sure that the sand was saturated.

As advised by the polymeric sand packaging, I also used the leaf blower to clear any standing water off the stones themselves, forcing it into the surrounding cracks. White haze is common and easy to clean (like when you’re grouting tiles in your shower or on your floor), but if I could prevent it on flagstones by breezing it away with a forceful air, I was going to do it.

Once it’s saturated and sits for awhile, you’ll immediately be able to feel it becoming more cement-like to the touch. After it was soaked, it looked like this:

After a few hours, it was noticeably compact. And once we left it to dry for 24 hours, voila! Beautiful.

The sand had hardened becoming cement-like, locking the stones together firmly. Hopefully they’ll hold together well for a long time; the winter months will be a good test to see how it holds up to freezing and thawing.

And stepping back, the patio as a whole looks beautiful. I immediately accented it with my old metal fire pit and some adirondack chairs that we recently acquired.

Note: It had rained the day I took this picture. The only noticeable flaw? A single rock on the left hand side of this photo sits just a hair lower than it’s neighbors. Didn’t notice it until it began sprinkling. Mini-pool. Live and learn. And try not to focus on it, because the other 98% of the surface is amazing and well-draining.

Our neighbor had a few trees cut down earlier in the year, and at that time we snagged a single piece of the trunk that had been cut very straight on both sides. My intention had been to dry it out and bring it inside as a side table, but it works really nicely out here too.

I hope some of you taking on your own patio projects! Overall, it wasn’t cheap but it would have cost a lot more if we hadn’t done it ourselves. Here’s the rundown:

  • 2 palettes of irregular flagstone = $840 (but we didn’t use all of it, and may find another use for it, or Craigslist it to get some of our money back).
  • crusher run stone, 2 yards: $100
  • base sand, 1 yard: $35
  • high-performance polymeric sand, granite gray, 2 bags: $70
  • approximate delivery charges = $165
  • TOTAL: $1,210.00

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