I recently built an in ground fire pit in my backyard using landscaping flagstone and construction adhesive. With a total cost of around $80 and an afternoon of work I've got a fire pit that will last a very long time. Here's how I did it!
Step 1: Gather Your Materials and Tools
I built my fire pit using 30 landscaping flagstones and 4 tubes of heavy duty construction adhesive. 30 stones will give me 3 rings of 10 with an approximate inner diameter of about 30 inches. The size of the fire pit is completely up to you, for a bigger pit add a stone or two to each ring, and for a smaller pit remove a stone. Keep in mind that the more stones you add you the more construction adhesive you may need. In addition to the flagstones and construction adhesive I also used a small level, pickaxe, flathead shovel, rubber mallet, small garden shovel, a small brush, and a caulking gun.
Step 2: Select Your Location and Lay Out Your Stones
Be sure when you're selecting a location for your fire pit you are a good distance away from your house, there aren't any low hanging tree branches above where the pit will be placed, and there is plenty of space around the fire pit for seating. Arrange your stones in a circular pattern. Be sure to get them as close and tight together as possible.
Step 3: Mark Out and Dig Your Hole
After you've arranged your stones in a tight circle use the pointed end of your pickaxe to drag a line around the outside of your stones. This will mark the outside edge of your hole. Once you've marked the outside edge of your hole, remove the blocks and start digging. The hole will need to be a few inches deeper than one stone is tall.
Step 4: Check Your Hole for Depth and Diameter
Once you feel like you've got your hole deep enough and it's dug out all the way to the line you marked, start placing your blocks inside to check that the depth and diameter are both good. If the hole is too small around or not deep enough remove the blocks and make the necessary adjustments. After you've got your hole to the right size and depth place your stones inside in a close tight circle.
Step 5: Level Out Your Bottom Layer of Stones
Making sure your bottom layer of stones are flat and level is the most important part of the build. With out a level and flat base the rest of the stones stacked on top won't be level or flat. Start by checking one stone with your level. Using your rubber mallet you can hit the stone in order to compact the dirt underneath it and get it to sit flat and level. After hitting it a few times, check the stone with the level again. Be sure to check both front to back and left to right with the level to make sure it isn't leaning forward or backward or side to side. If you're unable to get the stone level you may need to lift it up and either remove a high spot in the dirt underneath with the garden shovel, or add a small amount of dirt to raise it up. If you need to add dirt, just sprinkle it in loosely and allow the weight of the stone to compact it. Check it for level again and hit it with the rubber mallet as needed. Once you get one block level and flat continue the process around in a circle until you've leveled every stone.
Step 6: Brush Off the First Layer and Glue and Stack the Remaining Stones
Once the first layer is flat and level brush off any excess dirt to prepare for gluing the next layer. Apply a liberal amount of construction adhesive to the bottom of another block, turn it over and stack on top of the first layer. Over lapping two blocks on the layer below it. Continue gluing and stacking the remaining stones on the second level. Glue and stack the third level in the same way making sure you offset that level as well. Check the top layer for any wiggly blocks. If you find one, remove it and add a liberal amount of extra construction adhesive. Replace the block and allow it to settle down gently in to the pile of construction adhesive. This way when the adhesive dries the block will be firmly connected to the layer below.
Step 7: Back Fill the Edges and Compact the Dirt Around the Fire Pit
Once all the blocks are glued down, come back with some of the extra dirt you removed when digging the hole. Backfill around the edges and compact the dirt around the fire pit. Allow at least 24 hours for the construction adhesive to cure before starting a fire.
Step 8: Enjoy Your New Fire Pit
After the construction adhesive has cured for at least 24 hours, light a fire and enjoy your new fire pit!
For more info check out the video.