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How to Build an Indoor Brick Fireplace

Nothing says warm and cozy like an indoor brick fireplace. Building your own takes some hard work, but the end result can truly enhance the appeal of your home. To make this project a bit more manageable, try purchasing a fireplace masonry kit. This should include most of the supplies needed to complete this DIY indoor brick fireplace project.

Getting Started

First, select the area of you home you wish to install the fireplace. Some of the most common spots for a fireplace are the living room, dining room, and bedroom. Measure and mark out the area before you begin to make sure the spot you chose has the wall space required and viewing area you desire for your fireplace.

Constructing the Hearth and Fireplace Foundation

The standard size of the hearth is around 4 inches thick. The base of the hearth must be built while taking into account the weight of the chimney and firebox which it supports. It must also be deep enough for the hearth extension which is normally around 18 – 20 inches forward of the opening.

For the base, you must construct the hearth foundation about 3 inches below your current flooring. This will allow for enough room and support to accommodate the inner hearth and hearth extension.

Building the Frame

When building the framing for your fireplace, take into account at least 2 inches of space is required between combustibles and the exterior wall of the fireplace. Also the outer combustible wall should be at least 4 inches thicker than the framing masonry. This will prevent flames from extending past the combustible wall and can also allow for some decorative freedom for the mantel piece.

Inner Hearth Construction

Mix mortar by following the instructions on the packaging. When building your base, be sure to account for the amount of space needed to fit the firebox. Spread the mortar and begin to lay the firebrick base. Make sure to leave 1 1/16” wide joints between each brick.

Building the Firebox

Place the steel framed glass fire doors where you envision the opening of your fireplace, tape this area off with painters tape. This mark out will act as a guide for building the firebox.

Begin building the firebox using refractory mortar and firebricks. When laying the firebricks, make sure they are set so that they form the front edge of the covings while meeting the back side of your painter’s tape template.

Backing Up the Firebrick

In order to ensure the sturdiness of the base and frame, back up your firebrick with concrete block. Start by laying the 4 x 8 x 16 concrete blocks on the hearth base and build them up until the firebox walls are at least 8 inches thick. Make sure to leave air space between the masonry and outer shell during construction so the firebox has room to expand when it becomes hot.

Setting the Throat

Your kit should have come with a fireplace throat. This should be installed on top of the firebox using refractory mortar. Once the throat is set it will provide the fireplace with the correct firebox depth and fireback width. Now build up the masonry to the top of the throat creating a 13.5 inch platform above the fireplace opening. Once the platform has been constructed, you need to set the damper. Make sure the hinge of the damper opens and closes freely. When properly installed, the valve should open forward.

Forming the Smoke Chamber

Use vitrified clay to form a smoke chamber over the damper. Make sure the damper valve still opens and closes freely after forming the smoke chamber. Joint the clay together with mortar and build up the masonry about 4 inches thick around the chamber.

Building the Chimney

The chimney must be at least 4 inches thick around the flue in all directions and must extend at least three inches above the roof line. Using refractory mortar and firebrick, construct the chimney so that it is at least 4 inches away from the exterior combustible wall of your home.

Once you finish your fireplace, be sure to let the mortar set for at least a few days before lighting your first fire.