Building an outdoor fireplace with cinder blocks is a great way to add warmth and ambiance to your backyard. With some planning and DIY skills, you can create a beautiful and functional fireplace that will be a focal point for gatherings with family and friends.
Introduction
Cinder block fireplaces are durable, affordable, and easy to construct. The modular nature of cinder blocks makes them perfect for stacking and shaping to your desired design. With a little bit of masonry work, you can build a fireplace tailored to your space that will last for years.
A cinder block fireplace is also safer and more contained than a standard campfire or fire pit. The structure helps prevent sparks from escaping and reduces the fire’s exposure to winds. This allows you to enjoy the flickering flames without worrying about embers catching stray leaves or grass on fire.
Benefits of a Cinder Block Fireplace
Here are some of the main benefits of building an outdoor fireplace with cinder blocks:
- Durability – Cinder blocks are weather-resistant and can withstand high heat. A well-constructed cinder block fireplace can last for decades.
- Customization – The modular blocks make it easy to construct a fireplace in different shapes and sizes. Build it to perfectly fit your backyard.
- Cost-effective – Cinder blocks are an affordable DIY building material. Constructing with blocks costs less than materials like brick or stone.
- Portability – Cinder block fireplaces are not permanent structures. If needed, you can dismantle and move them to a new location.
- Safety – The fire is more contained than an open pit. This prevents embers from escaping and reduces fire hazards.
Planning Your Cinder Block Fireplace
Careful planning is required before beginning construction of your cinder block fireplace. Here are some key steps:
Choose a Location
- Pick a spot at least 10 feet away from your home, trees, fences or other structures. This prevents fires from spreading.
- Consider prevailing wind patterns so smoke does not blow toward the house.
- Check local building codes for any setback requirements or restrictions.
Design the Size and Shape
- Decide on overall dimensions based on your needs. Standard sizes range from 3-5 feet wide and high.
- Choose a traditional rectangular firebox or get creative with curved, rounded, or octagonal shapes.
- Incorporate decorative design elements like a chimney or hearth.
Select Safe, Heat-Resistant Materials
- Use solid concrete cinder blocks rated for high heat, not lightweight blocks.
- Choose heat-safe materials like steel, stone, or brick for top surfaces. Avoid flammable materials.
- Select a spark arrestor screen chimney cap to prevent embers from escaping.
Constructing Your Outdoor Cinder Block Fireplace
Once you have completed the planning phase, you’re ready to start construction. Follow these tips for building your fireplace:
Clear and Level the Site
- Remove any grass, plants or debris and level the soil.
- Compact the soil thoroughly before starting. This prevents settling issues.
- Consider adding a gravel base for extremely soft or uneven terrain.
Lay the First Course
- Place the blocks lengthwise to start the back wall of the firebox.
- Use masonry adhesive between each block for stability.
- Check that the first layer is completely level using a spirit level.
Build up the Back and Sides
- Continue stacking blocks to desired height, alternating direction between layers.
- Offset vertical seams between courses for better structural integrity.
- Construct side walls to match height of back wall as you build up.
Add the Front Wall and Smoke Shelf
- Leave front opening 1-2 feet wide depending on firebox size. This is where fuel is loaded.
- Construct front wall slightly shorter than back to create smoke shelf at top.
- Smoke shelf helps contain embers and allows smoke to vent up chimney.
Install Lintels Above Opening
- Place steel or masonry lintels above front opening and smoke shelf.
- Lintels support the structure above the gaps so courses don’t sag.
Complete Chimney and Top Surfaces
- Build chimney at least 5 feet above firebox opening for proper ventilation.
- Use cinder blocks or metal ducting for chimney then top with spark arrestor cap.
- Add thick, heat-safe surface material like stone, bricks, or concrete to tops of side walls.
Cure the Fireplace Before First Use
- Let mortar cure for 72 hours or per manufacturer instructions before lighting first fire.
- Curing slowly helps prevent cracks from developing.
- Do a test burn without prolonged exposure to high heat on the first fire.
Design Tips and Recommendations
- Incorporate vents under the smoke shelf in back wall to improve air circulation.
- Add decorative materials like stucco or stone facades for more visual appeal.
- Build the firebox taller rather than wider for better heat control and safety.
- Construct a hearth extension out of pavers or bricks to protect surrounding surfaces from sparks.
- Use high-temperature firebrick lining inside the firebox for added durability if desired.
Safety Precautions
Proper precautions should be taken when using your cinder block fireplace:
- Always have a fire extinguisher or water hose nearby when the fire is burning.
- Do not leave the fire unattended until ashes are fully extinguished.
- Avoid using flammable accelerants to light or stoke the fire.
- Extinguish the fire completely before going to sleep or leaving the area.
- Monitor children and pets closely around the hot fireplace.
- Allow ashes to fully cool for 2-3 days before removing to prevent re-ignition.
Frequently Asked Questions
How long does it take to build a cinder block fireplace?
With proper planning, an average cinder block fireplace can be constructed over 2-3 weekends as a DIY project. The total time will vary based on size and complexity.
What tools do I need?
Essential tools include a mason’s trowel, level, measuring tape, shovel, mortar mixing equipment, and masonry or concrete saw for cutting blocks if needed. Safety gear like gloves and eye protection is also recommended.
What type of mortar should I use?
Use Type S mortar for the high-temperature environment inside a fireplace. This mortar with lime content withstands heat better than other types.
How do I prevent the cinder blocks from cracking?
Proper block selection, using Type S mortar, and slowly curing the first fire helps minimize cracking. Maintaining proper drainage and not over-exposing the fireplace to water prevents freeze-thaw damage.
What maintenance does a cinder block fireplace require?
Remove ashes regularly, inspect for damage or cracks annually, and re-point mortar joints as needed. Taking preventative steps preserves the fireplace for many years.
Conclusion
Building a cinder block fireplace is an achievable DIY project that adds beauty and functionality to your backyard. With safety precautions and proper construction techniques, a cinder block fireplace can provide warmth and comfort for your outdoor gatherings for years to come. The modular nature offers creative options for designing a fireplace perfect for your space.