Ask the Builder: Pavers laid in sand are no match for burrowing animals

I installed an attractive concrete paver patio for my wife seven years ago. I knew it would fail, but I didn’t know when. She wanted the patio completed as soon as possible. This tight deadline dictated that I had to set the patio stones on sand instead of mortaring them to a steel-reinforced concrete slab.

My new flat patio soon was not so flat. The sand beneath the pavers was being transported away grain-by-grain by union members of chipmunk miners local 104. They found the sand easier to dig through than the sandy soil under my lawn. The concrete pavers provided a sturdy roof to keep their nests dry.

I live in central New Hampshire. The winters bring cold weather. Frost heave is a reality. The up and down seasonal movement wreaks havoc on things that rest on the soil. Ancient stone walls built two hundred years ago to outline livestock pastures tolerate this movement to a great extent. Flat patio and sidewalk stones not so much.

The greater threat is burrowing mammals like chipmunks, mice and who-knows-what. In my case, it’s chipmunks. These cute furry demons are as prolific in my neighborhood as the vacationers who overrun my state year round.

Chipmunks tunnel through soil like you might dig in a huge pile of styrofoam packing peanuts. It’s child’s play for the tiny creatures to create an extensive labyrinth of interconnecting tunnels. They do this for survival, and it’s baked into their DNA.

My large-format concrete pavers range in size from 8-by-16 inches all the way up to 16-by-24 inches. The pavers are 2.5 inches thick. They’re heavy. The chipmunks can’t move the pavers, but they can make them drop an inch or more by removing the dry sand beneath them.

My wife asked me to repair the uneven patio a month ago. Some small and medium pavers would tip back and forth as you walked on them. The last thing I want is for my bride of 50 years to fall and break her hip.

I didn’t know the extent of the damage when I came up with my repair plan. I thought at first that just a few stones needed to be lifted back up. I purchased a few bags of dry sand and a bag of pure Portland cement. I was going to mix three parts sand to one part cement and place it under the sunken pavers.

My plan was to start at one corner of the patio and work a rectangle that was about 5 feet wide and 12 feet long. I was stunned when I lifted up the first paver. Fifty percent of the sand was gone. A small maze of tunnels was under this large paver. The interconnecting tunnel system grew as I pulled up more and more stones.

Three pavers in the center of the patio required an emergency repair. I pried up a small 8-by-16-inch paver. I then lifted two adjacent larger pavers. I stood back in awe shaking my head looking down at the local chipmunk cafeteria.

Packed dried oak leaves were brought from outdoors. The chipmunks used these to create a nest. Next to this was a pile of 30 to 50 fresh acorns. The chipmunks, no doubt, were not happy that I had discovered their lair.

Sand and cement was not going to do the job. I had to come up with a permanent fix.

I purchased 25 60-pound bags of dry concrete mix. I also purchased ⅜-inch steel reinforcing rods. My new plan was to install a thin, flat concrete slab that the pavers would rest upon. The chipmunks would never harm this new 2-inch concrete slab.

The steel rods laid 16 inches on center in both directions would ensure the concrete would stay in the same plane over time. The chipmunks might recreate their tunnel maze in the gravel and soil under the slab, but the concrete will span the 2-inch-wide tunnels and not drop.

I removed all the old sand. The hole was now 4.5 inches deep below the top of the patio. My plan is to install the dry concrete mix in two 1-inch lifts. The first lift will be compacted and I’ll lay the steel rods on the mix. I’ll then install the second inch of dry concrete.

I’ll take great care in getting this second concrete mix layer flat to resemble the surface of the sand as I installed it seven years ago. I’ll then mist the concrete with water to start the hydration chemical reaction that transforms the concrete into artificial stone.

A day later I’ll lay the concrete pavers on the hard concrete. They’ll be installed in the exact same interlocking pattern as I did seven years ago. The chipmunks delight my wife, but for me they’ve become my back’s nemesis.

Your takeaway should be this. If you have tunneling mammals where you live, don’t use sand. Install dry concrete mix in place of the sand. Don’t forget to put in the steel rods.

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