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How to Build a Cultured Stone Outdoor Firepit

Approximate reading time: 6 Minutes

Add the style of stone, without the cost, to your outdoor firepit using cultured stone veneers.

What is cultured stone?

Cultured stone is a cost-effective solution for interior and exterior projects that provides the same beauty and performance of natural stone veneer.

Here's what you'll need:

Materials
  • Cement Board
  • Polymer-modified Mortar
  • Cultured Stone
Tools
  • Margin Trowel
  • London Brick Trowel
  • Gatorback Mortarboard
  • 5-gallon Bucket
  • Eggbeater Mixer
  • Mixing Drill
  • Masonry Brush
  • Utility Knife
  • Bucket Scoop
  • Level
  • Grinder with Masonry Cutting Disc
  • Screw Gun
  • Drill
  • Drill Bits
  • Circular Saw
  • Tape Measure
  • Wood Clamps
For Your Safety
  • Safety Goggles
  • Safety Gloves

Installing Cultured Stone

Cultured stone is made of concrete and many styles rival the look of natural stone or veneers, making it the perfect solution for cladding both interior and exterior home projects.  Since this stone is manufactured, it is more uniform and easier to cut, making installation simple. 

Working with Cultured Stone

The cultured stone we selected for our outdoor firepit has no visible mortar joints giving it a dry-stacked appearance.  The stone color can vary quite a bit, depending on the color pattern you choose. All of our stones have the same height, but they have long, medium and short lengths, along with corner pieces which make wrapping around an outside corner easy. As you apply the stone, you’ll want to mix the size, pattern, and color for a random look. 

The structure for our firepit was cladded in ½” thick cement board which is ready for masonry.  This saves you from having to prep the surface with additional lath materials or a scratch coat.  The stone can be applied directly to the cement board with a special polymer modified mortar.

Some stones will have to be cut to length to fit within the project.

 Grinder

A grinder and masonry cutoff wheel will quickly cut them in half. Sometimes stones have excess concrete from manufacturing around the back edges. A brick trowel will easily knock off any excess concrete. 

Step 1

Protect the surrounding areas

The first step is to protect the area that you’re working around. Construction paper and masking tape work great for patios, decks, and floors.

Next, set a spacer to keep the stone from touching the bottom surface. We used some scrap wood planks which were about 3/8” thick.

Dry layout the first row of stones to get an idea of how to place them.

Next, it’s time to mix the mortar.

Step 2

Mix Mortar

Following the manufacturer’s instructions, add the proper amount of mortar and water into a 5-gallon bucket.

Mix the mortar, checking for consistency as you go. It should hold firm on the trowel once it’s ready. If not, add more water and mortar mix.

Gatorboard

Once it’s mixed, pour it out onto a mortar board. This will make it easy to scoop the mortar onto the stone. Remove any additional mortar from the bucket with a bucket scoop.

Step 3

Install the First Row of Cultured Stone

Since the stone is manufactured, it is much more uniform and easier to cut, making installation simple.  You will want to start from the bottom of your structure, then stack by layer, moving upward.

Using a trowel, scoop a liberal amount of mortar and butter it onto the back side of the first corner stone. This should be applied relatively thick and cover the entire back.

Butter
Then position the first piece and press it into place, wiggling it for a good bond. Make sure it’s level and straight in both directions. The mortar on the backside should squish out some. 

SquishRemove any excess mortar with the trowel after the stone has been applied.

Now grab the next stone and butter up the back side with mortar. Place the stone and squish it into place. Again, remove any excess mortar after installation. 

Pro Tip

As you apply the stone be careful not to apply any pressure against the corner stone that’s already installed. Any pressure against stones that are already installed can break the mortar bond.

Continue to place stones towards the other end, occasionally checking the row with a level to keep them straight and flush.  A gentle tap with the bumper of your trowel can be just enough to line up a tile that may be a little out of place.  Be sure to mix and match the length, texture, and color for a nice random look! Note that the stones will vary in height slightly, so small gaps may appear in the narrow stones, but don’t worry because the small gaps add to the overall look and character of the stone.  As you approach the corner you’ll need to check and see if the corner block or last block before the corner will need to be trimmed. 

Step 4

Trimming the stone

If you prefer to cut a straight stone as opposed to a corner stone, go ahead and install the corner stone first. Check it for level and then go back to fill in with straight stones. This means that one of the straight stones most likely will have to be cut to length.

To cut a stone to length, first mark the location of the cut. Then transfer a straight line across the back side with a square. Using a grinder, cut into the back side.  Then flip the stone over and make a cut on the front face.

Mark        Cut back side        Cut front

Note:  The cutoff wheel may not cut all the way through. To remove the waste, you can usually just break the stone off by hand.

Pro Tip

When you cut cultured stone it will leave an exposed edge, which has no color. One way to hide a cut edge is within other stones. On areas where the edge will be exposed, bury the cut edge against another stone. 

Hide

Step 5

Stack Up Additional Rows

Continue working your way around to complete the bottom row. Once the first row is done, you can start on the second row. Our fireplace insert had a control panel and vent openings that we had to work around. Cut the stone to length to work around these open areas.

Control Panel

Remember to clean up excess mortar during installation. A masonry brush can help clean up small, dried chunks of extra mortar.   

Step 6

Install the Final Row

Once you get to the final row, you’ll more than likely need to cut the stone to a narrower height. A tile saw with a fence will cut it straight and accurately. Clamp the fence to the desired height and cut the stone with the back facing down. Then flip the stone over and cut it on the front side. If the cut doesn’t go all the way through you can break the stone in half by hand.

Cut the corner stones the same way, on the back with the face down first, and face up for the second cut. Then use the grinder to cut as deep as you can into the corner. Again, the stone will need to be broken apart since the blade won’t cut all the way through. 

Step 7

Finish Up

Once the rows are complete, it’s time to decide what to do for a top. We chose a concrete countertop with a black stain.

Final

Finally, call a local, licensed gas professional to connect your fuel components.

Be sure to check out MARSHALLTOWN’s high-quality tools to make your next cultured stone project a success! 

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