What Concrete Blocks Do You Use to Build an Outside Fireplace?

Adding an outdoor fireplace to your home can increase your outdoor ambiance while giving you somewhere warm to gather on cool nights. When it comes to the right concrete blocks for your fireplace, you can use more or less any concrete block available, because concrete blocks in a fireplace provide structural support. Before building a concrete block fireplace, you should understand how to use your concrete blocks and what other materials you need.

Close-up of texture and pattern of cinder block
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Purchase concrete blocks at a hardware store or building supply outlet.

Outdoor Fireplace Construction

Outdoor fireplaces employ concrete blocks for structural integrity and support. As a very hard, weather-resistant, relatively inexpensive material, concrete blocks make an ideal construction medium for independent outdoor structures such as fireplaces. When you build an outdoor fireplace, you use concrete blocks as support and protection for the overall structure of the unit, though the actual fireplace contains little or no concrete, because concrete blocks offer inferior heat resistance when compared to materials like bricks.

Types of Concrete Blocks

When it comes to building a fireplace, you can use any type of concrete block you want. Generally speaking, concrete blocks you purchase from a hardware store or supplier all exhibit the same basic qualities. When you buy blocks, you can tell the salesperson what you need them for to get the best quality concrete. However, references such as the Ace Hardware guide to working with concrete blocks generally recommend any generic concrete blocks you can find for fireplace construction.

Block Shape

You may need to use specially shaped concrete blocks in some applications when it comes to building your outdoor fireplace. For instance, if you want to build a circular fireplace or include circular elements, such as a round chimney, you should use manhole blocks, or concrete blocks specifically designed to surround circular areas. Or, if you want to taper your chimney, you can purchase concrete blocks with tapering sides. If you build the brick part of your fireplace in any shape other than a square, you need specially shaped concrete blocks to surround this area. Always design your fireplace before building, so you know whether you need specially shaped blocks, how many and in what shapes.

Other Material

Firebricks are almost always used to line the actual fire pit of your outdoor fireplace. This material is exactly what it sounds like, brick designed for use with fire. You also need a flue lining to fit within your concrete blocks. Usually made from clay, this flue lining rises from the firebrick area and serves the purpose of removing smoke from the fireplace. Avoiding the use of concrete blocks in applications more suited for brick and clay can help improve the lifespan and performance of your outdoor fireplace. You may also want to purchase a decorative facade to cement over the top of your concrete block fireplace frame, to add aesthetic value to the unit.