How To Build An Outdoor Fireplace With Concrete Blocks

Constructing an outdoor fireplace is a rewarding project that enhances the aesthetics and functionality of outdoor living spaces. A concrete block fireplace offers durability, affordability, and design flexibility. This article provides a comprehensive guide on how to build an outdoor fireplace using concrete blocks, outlining the necessary steps, materials, and safety precautions to ensure a successful and enduring outcome.

Planning and Preparation

Prior to commencing the construction process, meticulous planning and preparation are crucial. This phase involves selecting a suitable location, obtaining necessary permits, designing the fireplace, and procuring the required materials and tools. Neglecting any of these steps can lead to complications and delays in the project.

The first step is selecting an appropriate location for the fireplace. The location must adhere to local building codes and regulations, specifically regarding setback distances from property lines, structures, and flammable materials like trees and fences. It is recommended to consult with the local municipality or building department to ascertain specific requirements and obtain the necessary permits before any construction begins. The chosen location should also consider factors such as prevailing winds, visibility from seating areas, and access to fuel storage.

Designing the fireplace is a critical aspect of the planning process. The design should incorporate the dimensions, style, and features of the fireplace, as well as the materials to be used. Common design elements include the firebox size, chimney height, hearth dimensions, and any decorative features. Consider the overall aesthetic of the outdoor space when choosing a design. Blueprint or sketch a detailed plan with precise measurements. This will serve as a guide during the construction phase and will help ensure accuracy.

After finalizing the design, a comprehensive list of materials and tools needs to be assembled. Essential materials include concrete blocks, mortar mix, fire bricks, flue liners, gravel, rebar, and possibly decorative stone or veneers. The quantity of each material will depend on the size and complexity of the fireplace design. Required tools typically include a shovel, level, trowel, brick hammer, concrete mixer (optional), measuring tape, safety glasses, work gloves, and a wheelbarrow. Having all materials and tools readily available before starting construction will streamline the process and minimize disruptions.

Building the Foundation

A solid and level foundation is paramount for the structural integrity and longevity of an outdoor fireplace. The foundation must be capable of supporting the weight of the entire structure and preventing settling or shifting over time. Constructing a proper foundation involves excavation, gravel base installation, and concrete slab pouring.

Begin by excavating the area for the foundation to the specified dimensions and depth, as determined by the fireplace design. The excavation should extend beyond the footprint of the fireplace by at least six inches on all sides. The depth of the excavation will depend on local frost line requirements, but typically ranges from 12 to 24 inches. Remove any topsoil, vegetation, and debris from the excavated area.

Next, install a gravel base within the excavated area. The gravel base serves as a drainage layer and helps to prevent frost heave. Spread a layer of compacted gravel to a thickness of at least four to six inches. Use a tamper or plate compactor to thoroughly compact the gravel. Ensure the gravel base is level across the entire surface.

Pour a concrete slab over the compacted gravel base. The concrete slab should be at least four inches thick and reinforced with rebar for added strength. Construct a form using wooden boards to contain the concrete. Place the rebar in a grid pattern within the form, ensuring it is elevated above the gravel base using rebar chairs or small pieces of concrete. Mix the concrete according to the manufacturer’s instructions and pour it into the form. Use a trowel to smooth and level the concrete surface. Allow the concrete to cure for at least 48 to 72 hours before proceeding with the next steps. Keep the concrete moist during the curing process by covering it with plastic sheeting or burlap.

Constructing the Fireplace Structure

With a solid foundation in place, the next step is to construct the fireplace structure using concrete blocks. This involves laying the blocks in a staggered pattern, applying mortar evenly, and ensuring proper alignment and leveling. Building the firebox with fire bricks is also an essential part of this stage.

Begin by laying the first course of concrete blocks around the perimeter of the foundation. Apply a generous layer of mortar to the top of the foundation and the bottom of each block. Set the blocks in place, ensuring they are level and aligned. Use a level to check both horizontal and vertical alignment. Maintain a consistent mortar joint thickness of approximately 3/8 inch between blocks. Stagger the joints between courses to enhance the structural integrity of the fireplace.

Continue laying courses of concrete blocks, working upwards to the desired height of the fireplace. Apply mortar to both the horizontal and vertical surfaces of each block before setting it in place. Periodically check the alignment and leveling of the blocks using a level and plumb bob. Use a brick hammer to gently tap the blocks into place as needed. Remove any excess mortar from the joints using a trowel. As the walls rise, consider adding rebar vertically within the block cores for added reinforcement.

Construct the firebox using fire bricks. Fire bricks are specifically designed to withstand high temperatures and are essential for protecting the concrete blocks from the direct heat of the fire. Line the interior of the firebox with fire bricks, using fireclay mortar to adhere them together. Ensure the fire bricks are tightly fitted and that there are no gaps between them. The firebox should be large enough to accommodate the desired size of the fire and should have an opening for ventilation.

Installing the Chimney and Finishing Touches

The chimney is a critical component of the fireplace, responsible for venting smoke and combustion gases safely away from the outdoor space. Installing the chimney involves selecting appropriate flue liners, constructing the chimney stack, and ensuring proper draft. Adding finishing touches, such as decorative stone or a veneer, can enhance the aesthetic appeal of the fireplace.

Choose flue liners that are compatible with the size and type of fireplace. Flue liners are typically made of clay or stainless steel and are designed to withstand high temperatures and corrosive gases. The size of the flue liners should be proportional to the size of the firebox. Install the flue liners within the chimney stack, ensuring they are properly aligned and supported. Use mortar to seal the joints between the flue liners.

Construct the chimney stack using concrete blocks, following the same techniques as used for the fireplace walls. The chimney stack should extend above the roofline of any nearby structures to ensure proper draft. The height of the chimney stack will depend on local building codes and regulations. Add a chimney cap to prevent rain, snow, and debris from entering the chimney. A chimney cap also helps to improve draft and prevent downdrafts.

Enhance the aesthetic appeal of the fireplace by adding finishing touches. Consider applying a decorative stone or brick veneer to the exterior of the fireplace. This can be achieved using thin-set mortar and following the manufacturer’s instructions. Other finishing touches may include adding a mantel, hearth, or decorative accents. These elements can be customized to match the style of the outdoor space. Ensure all materials used for finishing touches are weather-resistant and suitable for outdoor use.

Following these steps carefully ensures a durable and visually appealing outdoor fireplace constructed with concrete blocks, creating a focal point for outdoor enjoyment.