Jim Cox
Jim Cox
  • Tutorial Team
  • Springfield, MO

Flagstone Firepit for the Backyard

4 Materials
$30
20 Hours
Easy

How I used leftover flagstones from an old flower bed and some easy concrete technique to create an outdoor space.
flagstone firepit for the backyard
When I bought my home, it had a firepit made of those stackable Home Depot bricks. I used it a few times, but didn't like the look. It was time to clean it all out. I filled this in with dirt, reseeded and started at a new location in my back yard.

(If you have a riding mower, get yourself a dump cart for this kind of work - Worth every penny)
flagstone firepit for the backyard
Here's me getting an idea of how big I wanted it in the new location. I simply scattered rocks around to get an idea of what look I might be after. The flagstones were lining a flower bed in front of the house that I recently gutted. The new location is nearer the house and back porch. Look for a future project on the porch upgrade involving this firepit too.

The metal pan on the right is a stainless tank-end from a local manufacturer. It was in the back yard when I bought the house. ( Previous homeowner was a welding instructor at the college where I teach electricity. Lots of unusual metal items here and there. )
flagstone firepit for the backyard
White spray paint to mark my boundary
I set the metal pan in the middle and started measuring, marking, and digging. The pan was 36" diameter, so I grabbed a tape measure and went 42" from the lip and marked the ground with white spray paint. This is still a mess, but I had not done much masonry and had no Idea where this was going yet. Total seat of the pants engineering. When working with rock, a good pair of leather gloves are your best friend.
flagstone firepit for the backyard
Here's kind of a before and after in the same shot. I filled in the dug portions with river gravel from the same flower bed, and began laying the flagstones on top of it. You can see the gravel between the stones on the left side of this photo just outside the shade.
flagstone firepit for the backyard
Here are the stones temporarily placed on top of the river gravel. Rock, twist, and grind the stones into the gravel so they have a solid base under them. You want the gravel to meet the uneven surfaces on the bottom of the flagstones. I even went as far as to stand on them, but be careful when you have something not too solid underfoot.
flagstone firepit for the backyard
After the stones were placed on river gravel, I then removed each of them one at a time, and put sand underneath. I got two tubes of traction sand from a friend that had hauled them around in their pickup all winter, and then three bags from the local home improvement store. This was to give me a bit more adjustment on leveling. Confessing, I did a poor job on getting all the stones the same height. A string and a couple of stakes spread across my work area, or perhaps a nice long level, would have helped immensely. My goal was to have the stones level with the lawn.
flagstone firepit for the backyard
Cottage cheese tub for scooping sand
once all the flagstones were set firmly on the gravel/sand base, I filled in the gaps with a "concrete sand" a mix from the local home improvement store.
flagstone firepit for the backyard
I made sure the concrete sand got down against the base of all the flagstones first
flagstone firepit for the backyard
I used a dry paintbrush to smooth the concrete sand down level between the flagstones
flagstone firepit for the backyard
Here is the concrete sand spread between the flagstones. Note that the concrete sand is also all over the rocks. I wanted to clean this off.
flagstone firepit for the backyard
I simply rinsed the tops of the flagstones with a gardening wand until I could see the color. By total accident, I discovered this was enough water to soak thru the concrete sand. I never mixed a thing, seriously. I kept the water flow slow enough that the sand didnt' get disturbed as the water ran off the top of the flagstones. I didn't touch it up after wetting it either (but there may be a letter "C" hidden in the work somewhere ; )
flagstone firepit for the backyard
Here is the wet concrete sand between approx 1/3 the flagstones. Note that I did the whole firepit in 3 sections, which is why the area to the right still looks so rough. Again I had no idea if this idea would even work, so I was experimenting one $6 bag of concrete sand at a time.
flagstone firepit for the backyard
Well guess what - it worked. Here's the firepit after I wetted the last stage of concrete sand. It looks pretty good for an electrical engineer, right?  . The bigger rocks in the middle around the pan were placed in the concrete sand after it was wet to give them a place to sit securely. Just to the right of the pan you'll see a piece of pipe I stuck in the ground. More on that in a later project, but I'll give you a quick hint: I love outdoor cooking ♥
flagstone firepit for the backyard
A good shot of the completed firepit last August.

I waited until the following April to post this project. I wanted to see how it held up all winter before encouraging anyone else to do this. My son and I tried to level a few spots out with mortar, but only made a mess and went back and chiseled it out. GET YOUR FLAGSTONES LEVEL the first time, you'll be glad you did. I've had to repair a small gap or two where the bermuda grass has crept in. Some charcoal starting fluid and a lighter have gotten rid of it in a few places and it hasn't came back. This project is 'easy' in terms of details, but it was a lot of down on your hands and knees work. BTW, the stones are level with the lawn, and you're looking at all the maintenance done 100% with a riding mower. I can put the left front mower tire on the flagstone and make a quick lap in under 10 seconds, so the maintenance is super-easy as well.

Next I plan on coating it with a clear gloss concrete sealer, first because I prefer the wet look, and second I'll bet less water under the stones will make it last longer, and perhaps keep the grass from coming back. Feel free to chime in with suggestions etc, and I'll edit the post if it will improve someone else's work efforts.

Suggested materials:

  • Sand ($6 ea)  (Lowe's)
  • Concrete Sand ($6 ea)  (Lowe's)
  • River Gravel  (recycled)
See all materials

Have a question about this project?

3 of 4 questions
  • Trish Widdershoven
    on Apr 13, 2018

    I have a flagstone patio but I can’t keep it clean! I live in the Pacific Northwest...read lots of rain so I get surface blackening over the winter (ie mouldy I guess?) I can’t power wash cause the flagstone just disintegrates...maybe it’s sandstone??? Any suggestions on how to clean it and then seal it so it doesn’t happen again????

    • Dia29963273
      on Apr 18, 2018

      Spray it with white vinegar straight or you can mix some Dawn dish soap with the white vinegar. Better than clorox for the environment. You may need to use a scrub brush and some elbow grease. I use this solution for almost everything inside and outside the home.


  • Trish Widdershoven
    on Apr 13, 2018

    I have a flagstone patio but I can’t keep it clean! I live in the Pacific Northwest...read lots of rain so I get surface blackening over the winter (ie mouldy I guess?) I can’t power wash cause the flagstone just disintegrates...maybe it’s sandstone??? Any suggestions on how to clean it and then seal it so it doesn’t happen again????

    • Carol
      on May 6, 2018

      I was also going to suggest white vinegar you can also add lemon juice to it as well. This also works great in laundry instead of bleach

  • Alex
    on Apr 14, 2018

    Great job! Regarding the tank bottom, how's it holding out regarding rust??

    • Jim Cox
      on Apr 20, 2018

      Oh by the way, it has a 2" hole in the center so water drains thru when it rains


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