How To Build Outdoor Fireplace Cinder Block

How To Build an Outdoor Fireplace with Cinder Blocks

Building an outdoor fireplace with cinder blocks represents a cost-effective and relatively straightforward way to enhance an outdoor living space. Cinder blocks, also known as concrete masonry units (CMUs), provide a durable and fire-resistant material for constructing a functional and aesthetically pleasing focal point. This article outlines the necessary steps involved in designing and building such a fireplace, emphasizing safety precautions and structural considerations.

Before embarking on the construction process, careful planning remains crucial. This planning phase encompasses selecting an appropriate location, determining the size and style of the fireplace, and procuring the necessary materials and tools. Compliance with local building codes and regulations constitutes a mandatory aspect of the planning process, often requiring permits to ensure adherence to safety standards and zoning requirements. Failure to obtain the required permits could result in fines or the need to dismantle the construction.

The choice of location should factor in prevailing wind direction, proximity to combustible materials such as trees and wooden structures, and the overall layout of the outdoor space. A level, stable surface is paramount for the foundation. The design should incorporate adequate ventilation for efficient combustion and smoke dispersal. The fireplace's size should align with the scale of the surrounding area, ensuring it doesn't overwhelm the space or appear disproportionately small.

Materials required for this project typically include cinder blocks, fire brick, mortar mix, sand, gravel, a reinforcing steel mesh, a metal firebox or fire-resistant liner, and a chimney flue. The quantity of cinder blocks depends on the size and design of the fireplace. Fire bricks line the firebox, protecting the cinder blocks from direct heat and extending the fireplace's lifespan. Mortar mix binds the cinder blocks together, creating a solid structure. Sand and gravel form the base of the foundation, providing drainage and stability. Reinforcing steel mesh strengthens the foundation. A metal firebox or fire-resistant liner provides enhanced fire safety and containment, and a chimney flue facilitates proper smoke venting.

Tools necessary for the construction process typically include a shovel, a wheelbarrow or mixing tub, a mortar mixing hoe or drill with a mixing paddle, a brick trowel, a level, a measuring tape, a hammer, a chisel, safety glasses, work gloves, and potentially a concrete saw for cutting cinder blocks. Proper safety gear protects the builder from potential injuries. The selection of quality tools ensures accurate and efficient construction.

Ensuring a Solid Foundation

The foundation constitutes the most crucial element of any masonry structure. A well-constructed foundation prevents settling and cracking, ensuring the longevity of the fireplace. The process begins with excavating the ground to a depth below the frost line, the depth at which the ground freezes in winter. The excavated area is then filled with a layer of gravel, which provides drainage and prevents water from pooling around the foundation.

A layer of sand is placed on top of the gravel, providing a level surface for the concrete pad. A reinforcing steel mesh is embedded within the concrete pad, adding strength and preventing cracking. Concrete is then poured into the prepared area, forming a solid, level foundation. The concrete should cure for several days before the cinder block construction begins. The curing process allows the concrete to harden properly, maximizing its strength and durability.

The dimensions of the foundation should extend beyond the footprint of the fireplace, providing a stable base. The foundation should be level and square, ensuring that the fireplace is built on a solid, even surface. Any imperfections in the foundation could translate into structural problems in the finished fireplace.

Constructing the Fireplace Structure

Once the foundation has cured, the cinder block construction can commence. The first course of cinder blocks should be laid carefully, ensuring that they are level and square. Mortar is applied between the cinder blocks, binding them together. A brick trowel is used to apply the mortar evenly and neatly. A level is used frequently to check the alignment of the blocks.

Subsequent courses of cinder blocks are laid in a staggered pattern, overlapping the joints of the previous course. This pattern, known as a running bond, strengthens the wall and prevents cracks from forming. Mortar should be applied liberally to all joints, ensuring a watertight seal. Excess mortar should be removed immediately with a trowel.

As the walls rise, openings can be incorporated for ventilation and access. These openings should be carefully planned and positioned to ensure proper airflow and functionality. Reinforcement can be added to the walls by inserting steel rebar into the hollow cores of the cinder blocks and filling them with concrete. This provides additional strength and stability, particularly in areas prone to seismic activity.

The firebox, the area where the fire will be built, should be lined with fire bricks. Fire bricks are specifically designed to withstand high temperatures and protect the cinder blocks from direct heat. The fire bricks are set in place with fire clay mortar, which is resistant to high temperatures. The firebox should be sized appropriately for the desired size of the fire.

Installing the Chimney and Ensuring Safety

The chimney flue is essential for venting smoke and gases away from the outdoor space. The flue should be sized appropriately for the fireplace, ensuring adequate draft. The flue can be constructed from metal or masonry. Metal flues are typically easier to install, while masonry flues offer a more traditional aesthetic.

The chimney should extend above the roofline of any nearby structures, preventing downdrafts and ensuring proper smoke dispersal. A chimney cap should be installed to prevent rain and debris from entering the chimney. The chimney cap also helps to prevent birds and other animals from nesting inside the chimney.

Safety constitutes a primary consideration throughout the construction process. Fire-resistant materials should be used throughout the fireplace's construction. The fireplace should be located away from combustible materials, such as trees and wooden structures. A spark arrestor should be installed on the chimney to prevent sparks from escaping and potentially igniting nearby vegetation.

The finished fireplace should be inspected thoroughly for any potential hazards. Cracks in the mortar should be repaired immediately. The fireplace should be cleaned regularly to remove accumulated ash and soot. The fireplace should never be left unattended while a fire is burning.

Building an outdoor fireplace with cinder blocks presents a satisfying project that enhances outdoor living. By following these guidelines and adhering to safety precautions, a durable and functional fireplace can be constructed, providing years of enjoyment. Careful planning, a solid foundation, precise construction, and diligent attention to safety are essential for a successful outcome.