Boulder Bench Installation

Stone bench on boulders

Stone bench on boulders

This bench was installed in Biltmore Forest. The supports are ‘finger’ boulders that I cut down to a suitable length. The seat itself is a step slab, precut by the quarry. It’s exactly four feet long and eighteen inches from front to back. What follows is a brief view of installing such a bench. Unfortunately, I didn’t take pictures showing how I cut the boulders down which was mostly chisel work with some grinding to take off the ugly lumps.

I start by placing the supports. The googly eyes represent the center of the holes, where we start digging. If the orientation of the bench isn’t obvious, it’s a good idea to have a piece of cardboard or paper the same size as the bench slab. A life sized template lets you twist it this way and that, until you find the place the bench wants to be.

Once the holes are dug, I drop the supports in, onto a tamped base of pea gravel. Getting the supports leveled to each other and the tops flat is absolutely crucial. I use a cup wheel on my grinder to level off the tops. This is the most time consuming part of the installation. I had tested the design and assembly in BENCHLAB, but the way the stones relate in the actual installation means this step has to be refined in situ. Happily, I like making dust.

With the supports in place, I pour concrete around their bases. The top surfaces are flat, but I have used the grinder with a diamond blade to score the tops, giving the mortar a place to adhere. There’s about 7-8 inches of stone underground.

The seat slab weighs over 500 pounds. I use a pair of pressure treated 2″ by 12″ boards as a ramp to get the stone from the truck bed to the ground. I make sure it comes down the ramp facing in the right direction, with the top up. Then we just walk it up the ramp.
The first step up is a couple chunks of 4″ by 4″ scrap. Next, we lift it up onto standard 8″ blocks. From there we step up to the 12″ blocks. At each level, we remove the previous step, so there’s one less thing to trip over. It’s a heavy stone, but we’re never lifting it more than four inches and just one end at a time. The 12″ block is close to the full height. I bring a couple of extra bits of board to place under the stone to make sure it’s above the height of the supports. You want to set the slab down on the mortar bed, not slide it across it which risks pushing the mortar off.

Full disclosure, my helper Gary was there to make this install happen. I have done it by myself, but an extra pair of hands really helps.
I put a bed of mortar across the top of the supports and we set the slab on top. To finish it out, I adjust as needed to make sure everything is level, clean up the mortar joints and re-grade the area.

Then, I test the bench.

Yup, works.