Concrete Block Outdoor Fireplace Plans
Build a durable, weather-resistant outdoor fireplace using concrete blocks. This complete guide covers design, materials, step-by-step construction, and safety for your backyard project.
Why concrete block? Concrete block (also called cinder block or CMU) is an affordable, fire-resistant, and structurally solid material for outdoor fireplaces. With the right plans, you can create a custom fireplace that lasts for decades — and it's a rewarding DIY project for intermediate builders.
Why Choose Concrete Block for Your Outdoor Fireplace?
Concrete block is one of the most practical materials for an outdoor fireplace. It handles high heat well, resists weather, and provides a solid masonry structure that can be faced with stone, brick, or stucco later. Many homeowners choose this approach because it balances cost, durability, and ease of construction. If you're still deciding between a built-in masonry fireplace and a freestanding unit, our built-in vs freestanding fireplace guide can help clarify the trade-offs. For those who prefer a simpler DIY project, our DIY fireplace hub offers many alternative designs.
Unlike wood-framed structures, concrete block won't burn, rot, or warp. It also holds heat well, radiating warmth long after the fire dies down. If you're considering an outdoor fireplace for a patio or covered area, a block structure can be designed to fit your space — much like the planning that goes into outdoor covered patio with fireplace and kitchen layouts.
Materials & Tools for Your Concrete Block Fireplace
Before you start, gather the right materials. The exact quantities depend on your fireplace size, but here's a general list for a typical 6-foot-wide, 8-foot-tall outdoor fireplace.
Concrete Blocks
Standard 8x8x16 inch CMU blocks. You'll need roughly 80–120 blocks for the main structure, plus half-blocks for corners.
Mortar Mix
Type S or N mortar for outdoor use. Plan on 6–8 bags of 80 lb mortar mix for a medium fireplace.
Fire Brick
For the firebox interior. Fire bricks withstand direct flames and high temperatures. You'll need about 30–40 bricks.
High-Temperature Mortar
For laying fire bricks. This is essential for safety and longevity. See our guide on high-temperature mortar for fireplaces.
Concrete Footing Mix
For the foundation. A solid concrete footer is critical — the fireplace is heavy and must not settle.
Rebar
#4 rebar for reinforcing the footing and vertical cores. This adds structural integrity.
Firebox Liner or Insert
Optional but recommended: a steel or cast iron firebox insert can improve efficiency and safety.
Tools
Masonry trowel, level, rubber mallet, masonry chisel, circular saw with masonry blade, mixing tub, wheelbarrow, shovel, safety glasses, gloves, and hearing protection.
Step-by-Step Concrete Block Fireplace Plans
Follow these steps carefully. If you're new to masonry, practice laying a few blocks on a flat surface before starting the actual structure. Also, check local building codes — some areas require permits for outdoor fireplaces. Our article on fireplace permit requirements explains what to look for.
- Plan and mark the layout. Choose a flat, stable area away from overhanging trees or structures. Mark the footprint with stakes and string. A typical outdoor fireplace is 6 feet wide, 3 feet deep, and 8 feet tall. Consider the proportions relative to your patio or room shape so it feels balanced.
- Pour the concrete footing. Dig a trench at least 12 inches deep and 8 inches wide around the perimeter. Add rebar, then pour concrete. Let it cure for at least 48 hours. The footing must be perfectly level.
- Lay the first course of blocks. Start at the corners and work toward the center. Use mortar and check level frequently. This is the base of your fireplace.
- Build up the firebox. After 3–4 courses of block, begin forming the firebox opening. Use fire bricks for the interior walls. The firebox should be lined with fire brick and high-temp mortar. Leave an opening for the chimney.
- Continue the chimney and outer walls. Keep laying blocks, leaving a flue opening. The chimney should extend at least 2 feet above the highest point of the roof or nearby structure. If you're unsure about venting, our chimney and vent guide is a helpful reference.
- Install a chimney cap and spark arrestor. This prevents water from entering and keeps embers from escaping. It's a small investment for safety.
- Finish the exterior. Once the block structure is complete, you can apply a stone veneer, stucco, or brick facing. This is where you can get creative — many homeowners choose surrounds for gas fireplaces as inspiration, even for wood-burning units. For a natural look, consider DIY stone fireplace techniques.
- Cure and season. Let the mortar cure for at least 7 days before lighting a fire. Start with small fires to gradually cure the fire brick and mortar.
Pros and Cons of Concrete Block Outdoor Fireplaces
Advantages
- Highly durable and weather-resistant
- Excellent heat retention
- Affordable compared to custom masonry
- Can be faced with any material
- DIY-friendly for intermediate builders
- Does not rot or burn
Considerations
- Heavy — requires a solid footing
- Labor-intensive to build
- Not portable
- Needs proper drainage to prevent cracking
- May require permits
- Chimney must be correctly sized for draft
Design Ideas for Your Concrete Block Fireplace
Concrete block is a blank canvas. You can leave it as-is for a rustic, industrial look, or cover it with stone veneer, brick, or stucco. Popular options include:
- Stone veneer: Gives a traditional, natural appearance. Our DIY stone fireplace guide covers techniques.
- Stucco finish: Smooth and modern. See stucco fireplace DIY for step-by-step.
- Brick facing: Classic and warm. Works well with DIY brick fireplace methods.
- Shiplap or wood accents: For a farmhouse look, though wood should be kept away from the firebox. The DIY shiplap fireplace tutorial is useful for accent walls.
If you're building an outdoor kitchen or patio area, you might also consider incorporating a pizza oven or a smokeless fire pit nearby for a complete outdoor living space.
Safety & Maintenance Tips
An outdoor fireplace is a great addition, but safety comes first. Always keep a fire extinguisher nearby and never leave a fire unattended. Clear away leaves and debris from the area. Inspect the chimney and firebox annually for cracks or blockages. For ongoing care, refer to our outdoor fireplace maintenance guide. Also, ensure furniture and decor are kept at a safe distance — the principles in furniture distance from fireplace apply outdoors too.
If you're using the fireplace for cooking, never use accelerants. And if you live in a wildfire-prone area, check local regulations about outdoor burning.
Frequently Asked Questions
How long does it take to build a concrete block outdoor fireplace?
For a typical DIYer, expect 2–4 weekends. The footing needs curing time, and mortar must set between courses. Rushing can compromise structural integrity.
Do I need a permit for an outdoor fireplace?
Many municipalities require a permit for any masonry fireplace, especially if it's permanent. Check with your local building department. Our permit requirements guide explains the general process.
Can I use regular concrete blocks for the firebox?
No — regular CMU blocks can crack under extreme heat. The firebox interior must be lined with fire bricks and high-temperature mortar. The outer structure can be standard concrete block.
How do I prevent smoke from blowing into my patio?
Chimney height and draft are key. The chimney should be at least 2 feet taller than anything within 10 feet. Also, check for proper airflow. Our fireplace smoke problem article covers common fixes.
Can I convert my concrete block fireplace to gas later?
Yes, but it requires planning. You'd need to run a gas line and install a gas insert or log set. It's easier to plan for this during the initial build. See converting wood-burning fireplace to gas logs for details.
Ready to start your project? Compare top-rated outdoor fireplace kits and inserts to complement your concrete block build.
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