How To Build An Outdoor Fireplace With Cinder Blocks

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Outdoor fireplaces are a fantastic way to enjoy your backyard at night, even on cold weather. However, one question we often receive from homeowners is “How do I build an outdoor fireplace with cinder blocks?”

One of the advantages of building your own outdoor fireplace is that it can save you a lot of money on contracting costs while adding an application and appealing element to your outdoor space.

Admittedly, anyone can throw some block, brick, and mortar together and call it an outside fireplace, and a whole lot of people are eager to collect your money and do the job for you.

But unfortunately, there is no guarantee that the outcome will be well designed for smoke draw and safety. A good and functional fireplace is designed with accuracy.

However, the good news is that any DIYer can easily build an all masonry outdoor fireplace, you just need the right instructions, which is what you’ll get here.

That said, if you want to know how to build an outdoor fireplace with cinder blocks, that’s what the article is all about.

What is an Outdoor Fireplace?

An outdoor fireplace is typically a place for building fires outside of a home. Just like an indoor fireplace, an outdoor fireplace is usually added to a concrete patio, brick, or stone.

It’s usually made up of a firebox and a chimney, where the firebox is constructed with an incorporated smoke shelve although straight firebox designs are common since chimney draft is not always a problem for an outdoor fireplace.

Similar to indoor fireplaces, an outdoor fireplace requires regular cleaning and maintenance to ensure it always looks and performs at its best. Additionally, regular cleaning of an outdoor fireplace will help to keep it reasonably tidy and maintained and to also remove ash build.

Finally, an outdoor fireplace can serve as a decorative element, which lets homeowners enjoy a crackling fire while enjoying in their backyard.

What Are Cinder Blocks Used For?

Cinder Blocks

Cinder block (also known as concrete masonry units (CMU)) are generally used for building outdoor structures like fireplaces, pizza ovens.  Most people will refer to them as cinder blocks but there is a bit more technical term for them.

Cinder blocks come in different sizes and shapes for your outdoor projects.  There are solid ones, tall ones, short ones, and some are made with holes/voids.

Not only do they come in different sizes, but some cinder blocks that are classified with the same size can be a bit different allowing them to be used in a different way.

When shopping for concrete blocks, you only need to address them as cinder blocks and know a little about their sizes.  That said, the cinder blocks sold in the US are sized in inches.

Importance of Outdoor Fireplace in a Home

Outdoor Fireplace

Custom fireplaces can be integrated into nearly any part of a landscape to offer comfort, warmth, artistic appeal and functionality to a backyard.

Hardscaping elements such as fire pits and outdoor fireplaces can equally increase your home’s value when properly done, which is why they are massively gaining popularity amongst homeowners nowadays.

Additionally, an outdoor fireplace provides light and warmth to your backyard space during the colder winter months. Even when there’s snow, a fireplace creates a comfortable and unique atmosphere for your family and guests that will limit the chill. Not to mention, it’ll always give you a good reason to throw a party.

There is something thrilling about getting warm next to a fire, especially when it’s outdoors.

Read more about the benefits of an outdoor fireplace here.

Materials Needed For Your Outdoor Fireplace

  • Concrete cinder blocks
  • Stacked stone
  • Backer board
  • Chimney cap
  • Shovel
  • Water
  • Concrete trowel
  • Nails
  • Screwdriver
  • Mortar
  • Protective gloves
  • Tamper
  • Fireplace grate and a black pipe
  • Tape measure
  • Chalk
  • download
  • Cold chisel
  • Grinder, drill, and crowbar
  • Masonry hammer
  • Refractory mortar
  • Wheelbarrow or concrete mixer
  • Bar Clamp

How To Build An Outdoor Fireplace With Cinder Blocks

How To Build An Outdoor Fireplace With Cinder Blocks 2

There are basically many ways to build an outdoor fireplace with cinder blocks, but we’re going to cover the basic steps here. You can modify your fireplace as needed depending on your design.

1. Consider the purpose of your outdoor fireplace

There are several reasons you might decide to build an outdoor fireplace, but regardless of your reason, you will want to consider a few things to make your project a success.

Ambiance: Outdoor fireplaces can put you in the mood. A warm open hearth will provide an intimate setting for you, your family, and friends. If you like throwing parties in your home, consider building an outdoor fireplace with two open ends to contain more people.

A fire pit provides views from all viewpoints and the feel of a campfire setting, having one at the backyard of your home won’t be a bad idea.

Functionality: You can also build a fireplace that serves as a pizza oven or barbecue, but these designs are usually difficult. Additionally, think of any electrical installations (such as lighting or audio/visual cables) you may need to hide behind the fireplace.

2. Create a Dimension

Once you’ve decided what purpose your fireplace will serve, the next thing is to start the designing process.

In this case, you need to start by creating a dimension for the fireplace. The good thing is that your fireplace can be of any size, it all depends on what you want.

If you have an indoor fireplace in your home, then you can measure it to get an idea of standard fireplace measurements.

3. Build the Foundation

Now, let’s build the foundation of your fireplace. To do this, follow the steps below:

Step 1: Dig up a flat rectangular area of the soil about 10% larger than the footmark of the planned fireplace until you reach a firm subsoil. Standard sizing may be “3 x 4 or 4 x 6 feet” and subsoil is often at a depth of 4 to 6 inches.

Step 2: Using a tamper, compact the base of the excavated area and spread two inches of gravel or more in the bottom for drainage.

Step 3: Create a rectangular frame with 2 x 6s of the same size and shape with the foundation and let it rest on top of the gravel. Adjust the gravel’s grade as required to make the frame level.

Step 4: Cut support elements out of 2 x 4s with one pointed end, and hammer them into the ground in different places next to the edge of the frame to prevent the concrete’s pressure from bending the 2 x 6s.

Step 5: Fill up the frame with concrete and let it set for 24-hours before moving to the next step.

4. Build the Fireplace Base

The fireplace will mount on a cinder block base on the foundation. These are normally the height of 2 or 3 cinder blocks and are always 3-sided so one can store firewood on one side.

However, you can build your fireplace according to your own design following the steps below:

Step 1: Spread a 1-inch thick layer of cement in an 8-inch wide strip around the concrete’s perimeter pad and put the first sequence of cinder block on top of it – spreading a half-inch layer of cement in the vertical joints between each of them.

As you move on, you want to ensure that each block is level, plumb, and square.

Step 2: Spread a half-inch layer of cement on top of the first sequence of cinder blocks, and install the 2nd sequence. This sequence should be offset from the first one so that each cinder block connects the joint between the two under it.

Additionally, you’ll be required to cut the last block in this sequence by half so comes even with end of the first sequence.

Step 3: Keep on laying cinder blocks until you reach your desired height.

Step 4: Spread a half inch thick layer of cement on top of the last sequence and install the hearth block on the top of the cinder block base.

Chimney Cap and Hearth Walls

Chimney Cap and Hearth Walls

The fire will be sited on the hearth block and the 3-sided hearth wall structure will contain the flames. Also, the footprint of the walls can be the same as the base or you can slightly bring them in to create a shelf on the outside of the hearth walls.

The ideal height is 3 or 4 feet is, but they can be adjusted based on your own choice. The chimney cap will be supported by the hearth walls.

Now, have the following in mind while building the hearth walls and chimney cap:

  • The hearth walls should be built with the cinder blocks in the same manner you constructed the plinth
  • Once the cement has cured for about 24-hours, mortar a base of hearth brick on top of the fireside block using a heat resistant mortar
  • Using a 3/8-inch joint of refractory mortar, mortar fireside bricks on the 3 hearth walls interior
  • Spread a 1/2-inch thick layer of mortar on the last segment of the fireplace walls and then install the chimney cap

Install The Exterior Veneer of Your Fireplace

The last step on how to build an outdoor fireplace with cinder blocks is to cover the exterior of the cinder block with a beautiful surface. This could be stucco finish, manufactured bricks, or just a natural stone. It all depends on your preferred visual style.

You can also consider trimming the exterior at this point. For instance, you may choose to install a curved opening for the hearth, which will need a wooden frame to support it.

Additionally, the materials you chose for the exterior finishing will also determine the installation tactic, in this case, it’ll be better to just go with the manufacturers’ specifications.

Outdoor Fireplace Style Options to Consider

Outdoor fireplaces come in different designs and looks and can be gas burning or firewood. If you decide to use gas, it’s important to get a professional for this part so he can install the gas lines and logs once you’re done building your fireplace structure.

There are equally outdoor fireplace kits that make the process of building one pretty easy and also makes it easy to get a particular style.

Some style options you can consider include pizza oven fireplaces, stacked stone fireplaces, and kiva-style or adobe designs.

Frequently Asked Questions about Outdoor Fireplaces

Can you build a fireplace with concrete?

Fireplaces must be built with heat-safe materials such as concrete, brick, stone, or block for the exterior. Also, the firebox (where the flames burn) must be built from fire-rated bricks or steel that can endure extreme heat.

How much does it cost to build an outdoor fireplace?

Usually, an outdoor fireplace will cost anywhere from $1,500 to $20,000. However, it will basically cost an average of $3,000 to build a fireplace.

Unfinished contractor models and pre-made kits typically cost from $1,500 to $9,000, while custom projects usually cost from $8,000 to $20,000, depending on your choice.

However, if you decide to build your own outdoor fireplace yourself, the cost will be much lower as you won’t have to pay a contractor. Good enough, you can do this by simply following the steps shared above.

Do I need a permit to build an outdoor fireplace?

You may not necessarily need a building permit to build an outdoor fireplace, but you will probably need permits for any plumbing or electrical work.

How thick should the fireplace footing be?

Masonry fireplaces footings and their chimneys must be built with solid masonry or concrete of at least 12 inches (305 mm) thick, it’s also important to extend at least 6 inches (152 mm) beyond the foundation wall on every side.

For a better understanding of this DIY project, here’s a short video that’ll also show you how to build an outside fireplace with concrete:

How to Build an Outdoor Fireplace with Concrete Blocks | Summary

I believe by now you already know how to build an outdoor fireplace with cinder blocks. But remember, this is just one of the steps.

After you’ve built your fireplace, you can then start decorating your new outdoor room to your taste so you can enjoy it to the fullest. For example, adding solar deck lighting will improve the attractiveness and ambiance of your fireplace.

Remember also that you can hire a contractor to do all the work for you, but we always recommend doing it yourself as this will save you a lot of money in the end. Building a fireplace will not only bring you and your family lots of outdoor fun but will also add value to your home.

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