Construct a Fireplace Method

The processes that are listed below to construct a fireplace are neither theoretical construction methods for a one-story fireplace nor standards and regulations. A stone fireplace wall surrounds the finished fireplace. The fireplace is flush with the wall and has a raised hearth that extends into the space. Brick is used to veneer the wall and the chimney on the exterior. This process is similar to the construction of masonry heaters.

This fireplace required a total of 1,100 bricks for the chimney, 600 bricks for the backup walls and throat, 75 bricks for the firebox, and 700 bricks for the shell. The foundation’s concrete blocks and the stone veneer are not included. It will take roughly 64 hours of labor to complete the fireplace for 4 skilled workers.

Step 1: The Foundation

Construct the majority of the fireplace foundation in tandem with the concrete basement wall by the concrete contractor. Simply pull the ash pit out beneath the fireplace of the 10-inch thick basement wall. In order to block off the fourth side of the ash pit, fill it with concrete masonry and leave a cleanout door in the wall for ash removal.

foundation of the fireplace

The firebox size is used to calculate the size of the fireplace foundation. In this instance, a first-floor firebox that was 3 feet wide needed a base that was 6 feet by 2 feet.

Step 2: The Foundation Top

Position the two sets of 4×6-inch angle irons from the foundation’s exterior wall to its interior concrete masonry wall at the top of the foundation. Seal the top by placing three rows of half-concrete blocks on the angle irons.

foundation top of the concrete fireplace

The half-shells are cut longitudinally from 4-inch-thick blocks, leaving room for a concrete hearth surface. Secure the blocks with mortar that is poured on the angle irons. Later, ashes are allowed to fall into the ash pit by punching a hole through the middle row of bricks with a wooden tool. To make hole punching simpler, this row of blocks is placed flat side up.

Step 3: Fireplace Outer Walls or Shells

Build the fireplace’s outer walls or shell. Use the brick to construct the shell, and for aesthetic purposes, rake the mortar joints. The shell is nine and a half bricks wide and three bricks in height when it is completed, reaching the top of the first story. Apply a Type N mortar to the interior to seal and weatherproof the shell.

constructing the shell

Step 4: The hearth

Place a reinforced concrete slab on top of the block halves that make up the ash pit’s roof. This slab supports the firebox and the higher outer hearth by cantilevering from the block infill wall. Cut into the room’s wood floor a rectangular hole to make place for the cantilever and raised hearth. The soffit of the cantilever is constructed using a temporary plywood sheet.

hearth for fireplace

Install the plywood sheet from the top of the block infill wall across the floor opening to a parallel floor joist. Position it at the joist and fasten with a nail to the top of a 2×4 that has been fastened to the joist’s side.

The plywood begins to lean forward from the block wall as a result, making the slab 20 inches into the room thinner and lighter. The #5 rebars are positioned every foot to reinforce the slab. The ash pit’s entrance hole is left open.

Following the setting of the concrete slab, the hearth is further stacked, first with a course of concrete blocks and subsequently with a course of regular bricks. The height of the hearth, which can be elevated as high as 1 1/2 feet or level with the floor depending on the owner’s preference, is determined by the number of brick courses.

hearth of the firebox

Chip off above the basement foundation wall along each side of the fireplace’s wall a small, 5-inch-wide piece of the wood floor is also. The final step is filling the resulting gaps with concrete to support the fireplace’s stone veneer front.

Step 5: The firebox

Place the firebrick floor of the firebox over the regular brick. The firebrick floor, also known as the inner hearth, is four bricks wide and five bricks deep. Set as closely together as possible (1/8-inch joints) the firebrick with refractory mortar.

Do note that making the joints too wide, is the most typical error made when creating the firebox. Wide joints could deteriorate more quickly.

Place on the shiner-side position the bricks for the side and back walls (the Brick Institute of America, however, recommends the thicker wall created by stretchers). The side walls are two bricks long and three bricks wide on the back wall.

Establish the angle between the rear wall and the side walls by this arrangement with the damper’s angle.
Flare out the side walls to the firebox opening, which is four bricks wide, while the back wall is centered on the floor (32 inches).

Carve the angles with his trowel that aren’t visible and don’t need to be exact. These are some of the bricks that make up the back angle.

Step 6: The firebox slope

The firebox must start to reduce to the size of the damper at a certain course height. The final four courses of the back wall are slanted toward the fireplace opening.

Each course had a 1-inch incline. On the end brick of the side walls, carefully measure and mark the angle. Then use a saw to cut the brick while maintaining the correct angle.

The back wall is then carefully placed at that angle. The bed joints of the first course that is slanted is laid thicker at the back of the joint than at the front in order to slope the back wall. The back wall should be higher if the angle is cut into the brick, and the side walls as well.  

sloping the firebox

The firebox’s back wall shouldn’t be curved. It looks less appealing to curve it because it is more challenging to align joints.
Fill the chips and cracks in the mortar seams after building the 31 3/4-inch-high fireboxes with a pointed trowel.

Step 7: The damper

Install a steel angle lintel from side wall to side wall across the fireplace opening once the firebox has been constructed. Leave the last course of each side wall about two inches short in the front to accommodate the lintel. The lintel supports the damper and the masonry above the firebox opening (known as the fireplace face).

After installing the lintel, place a 36-inch-wide damper, laying it on a bed of mortar laid over the lintel and the top course of the firebox. In order to prevent smoke from escaping out the fireplace front, put the mortar on the lintel to seal the seam. For this step, utilize ordinary mortar; refractory mortar is only used in the firebox.

Install the damper a few courses above the lintel rather than immediately on it, according to the Brick Institute of America (BIA). Wrap the damper in a compressible, combustible material, such as fibrous insulation, and then place it atop a thin layer of mortar to allow for thermal expansion and damper movement during fireplace operation.

Install an extra lintel above the damper to prevent it from bearing the masonry load. The thermal expansion of the damper may cause tension and cracking of the masonry if it does bear on the damper.
Additionally, put a compressible, noncombustible material at the steel angles’ masonry-embedded ends.

Step 8: The Throat

Cover the damper with four courses of bricks, leaving space for the damper door to open upward.
Corbel the side and front walls an inch at the fifth course, while leaving the back wall straight. The throat, also known as the smoke chamber, is corbeled an inch in each course until it is 10 1/2 inches wide, or the breadth of the square clay flue tiles that line with the chimney.

working the fireplace's throat

Divide the horizontal distance to be corbeled by the number of courses to determine how much to corbel each unit. The National Fire Protection Association (NFPA) 211 states that smoke chamber walls shouldn’t be taller than the width of the fireplace entrance and shouldn’t slope greater than 45 degrees from the vertical. The minimum thickness for walls should be 8 inches, or 6 inches if firebrick is used as the lining. Additionally, they need to be at least 2 inches away from combustible materials including drywall, exterior sheathing, and wall studs.

Install the final two courses before the flue liner as headers, per BIA, and should be cut to a length that completely supports the flue liner’s perimeter without impeding the flue liner opening.

Lay the first flue tile after mortaring the throat’s top. To seal the neck, apply the mortar to the outside.

Step 9: The Backup Wythes

Erect the firebox while also laying two wythes of regular brick around it. They merely serve to protect the firebox from fire. These wythes don’t need to be carefully laid because they aren’t exposed.

Fill the remaining spaces between the firebox and the shell with the concrete block once the backup wythes reached the height of the damper. Used masonry block because it could be stacked more quickly than several courses of brick. Position the blocks above the first-floor ceiling, supporting the chimney’s raked stones (Step 11).

making the backup wythes

Step 10: The fireplace’s front

Complete laying the brick support for the fireplace face once the throat is attached to the chimney flue. In order to apply the final stone veneer finish, insert corrugated flexible wall ties in the brick bed joints.

building the fireplace shell

Step 11: The chimney 

Since NFPA 211 calls for nonwater-soluble refractory cement, apply mortar together to the flue tiles from end to end and place them as the chimney is being constructed around them. Put the bricks to match the tile height as each tile is added.

The chimney will rise over the house’s roof from the fireplace’s throat. It needs nine and a half flue tiles and is six and a half bricks wide. Reduce the shell of the building to the width of the chimney by slicing it on a rack from the outside. Cover the racked face with thin, rectangular stones.

fireplace's chimney

Without the stones, it is necessary to lay numerous battered courses of brick to narrow the shell to chimney width. The stone supplies a good, weather-resistant surface. To create a place for the chimney, cut a hole in the roof overhang using a chain saw or equivalent tools.

The highest point of roof penetration must be 3 feet higher than the chimney top, which is required by code to be 2 feet higher than any component of the roof within 10 feet. The chimney top in this instance is 16 feet from the roof’s apex. For the fireplace to get a favorable draft, built the chimney 2 feet higher than the peak.

Step 12: The chimney cap

Leave a space on each side of the flue when it is centered in the rectangular chimney shaft. Under the next-to-last chimney course, insert a short steel conduit tube across the gap to seal it off. The top two courses of brick should then be positioned on the tubes, with the last course being placed about 8 inches below the top of the flue tile to make room for the cap.

The last course protruded 5/8 inch past the course underneath it in order to make a recess for pouring the cap, to form a drip, and for aesthetic purposes.

chimney cap

Set a rectangular timber frame on the edges of the last course and fill it with concrete to create the 4-inch-thick concrete cap. Take down the wooden structure after the concrete hardens. Finished the chimney by covering the flue tile with a spark arrestor screen, a square wire basket that prevents fly ash from exiting the top of the flue.

To stop water ingress, BIA advises using flashing cast-in-place caps. Between the cap and the brick chimney, flashing also acts as a bond break. A minimum 1-inch air gap should be left between the flue tile and the cap to allow for the vertical thermal expansion of the flue tile. A polysulfide, butyl, or silicone sealant filled the air space and was held by a backer rod.

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