A few years ago, my husband and I set out to build the most amazing fire pit, built right into our deck. Two years later, and that fire pit is the best gathering spot on any summer night. Roll up your sleeves and prepare to get a little dirty (and scraped, and scared, and sweaty...), once the pit is done you'll have created a perfect outdoor living space for you, your friends, and family.
Once you've located the perfect spot for your fire pit, and you have all of the necessary permits or permissions required, begin grading the dirt so that it is level. I'm not going to include deck building instructions, that's to complicated for one article, but if you are building a deck around the pit, mark it out now and start installing the footings. Also for the deck, make sure your fire pit is sitting square with in the deck space. If it's off, even a little, that's going to make some difficult lengthwise cuts on your decking.
Start your first level of your fire pit. 3 cinder blocks, end to end on the long side, holes up. That's the first side, then the 2 short sides get 2 more cinder blocks, end to end; and that should leave just enough space for the final side to get 2 more cinder blocks to squeeze in and make a rectangle. You should have used 9 blocks total. It's hard to explain so please refer to the picture:
Make sure this first level is level. Mix up a batch of the mortar according to the package instructions. You need to mortar between each block and that means removing the cinder blocks one-at-a-time and smoothing on the mortar between each block. Scrape away the mortar that "oozes" out on the outside sides. You can do the same for the inside "ooze" but it's not as important. The outside needs to stay smooth for the veneer layer.
Work quickly so your mortar doesn't dry up. Begin assembling the next layer, alternating the side with the 3 full cinder blocks to the opposite side of the rectangle. This will help stabilize the structure and lock everything together as the mortar dries. You'll need to mortar between every cinder block and spread an even layer of mortar between each layer. Check for level and lightly tap down any high spots. Keep the mortar "oozes" cleaned up on the outside.
Before you finish the last level, lay in the 4 pieces of re-bar, lengthwise. Space evenly. This re-bar is going to be what holds the grates on and the grates are what the wood will sit on when burning. The grates will be easy to remove for cleaning out the pit. Mortar the final level of cinder blocks. Just so you know: the re-bar is going to throw off your levelness on the top of the pit. You could notch out the cinder blocks so that the re-bar can lay flush or shim the rest of the blocks to be the same level. We didn't do either, and it turned out fine (just not perfect). Once the mortar dries, this would be the ideal time to finish building the deck around your pit.
Veneer! Out of 50 different kinds of stone veneer, we chose the river rock because it fits with our Northwestern style. This was also the most expensive part of our fire pit. There are many different schools of thought on how to lay out your veneer so that it looks natural. Make a template and lay out the stones, then mortar in place from the template arrangement is one popular way. We started with one side at a time, corners went on first. Mix up your batch of mortar that is specifically made for veneer. It's similar to tile, you smooth the mortar onto the back of the stone (frosting the stone like a cupcake) and "glue" or attach it to the cinder block. Continue all the way around, keeping your mortar bucket mixed. Now go back around and make sure everything is still attached and you are finished with this step. Let the mortar dry (or cure) for 2 days.
After the stones are set, use a flat head screwdriver to remove any excess mortar between the stones. It's time for grout. Mix up the veneer grout according to the instructions. You can use a grout bag, just like a frosting bag, it fills the grout in between the stones. We used the trowel and just packed the grout into the spaces. Keep the grout off the stone fronts/faces. You might want to keep a wet sponge nearby to wipe away any grouting accidents. (Oh yeah, tape off the deck before you start).
Almost done: Arrange the cap pieces along the top. We rented a concrete cutter (maybe it was a heavy duty tile saw?) so we could get those mitered edges. The cap stone also had to be cut to fit, depending on what cap stone you choose to use, it may be worth renting the cutter. Mix up one last batch of mortar to attach the cap stones to the tops of the cinder blocks. Make sure you keep the mortar off of your veneer face. Then you can fit the grill racks onto the re-bar shelf (we had to bend the ends of the racks to fit, we used a vice and a big pair of channel-locks, it was easy).
note Husband remembers using heavy-duty silicone to attach the cap stones.
Give your pit another 48 hours to set and you are ready to burn!