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Are Cinder Blocks Good For Fire Pits? (Essential Reading)

by Lianne Jones May 25, 2022

Are Cinder Blocks Good For Fire Pits?

If you have always wanted a fire pit but thought it was too big a job or too expensive to build, think again. We have put together all you need to know about building a fire pit using cinder blocks.

Cinder blocks are a great way to make a simple fire pit that you can enjoy all year round.

They are lightweight and inexpensive, ideal for a weekend project that you and the whole family can do together.

So let us guide you through the process of building a fire pit and making your backyard the place to hang out this summer. 

Is A Cinder Block The Same As A Concrete Block?

Cinder blocks and concrete blocks are both concrete masonry units (CMU) and are made from three basic elements, cement, water and aggregate.

Traditionally, concrete blocks were manufactured using stone aggregates, which made them quite heavy.

In the early 20th century, in an effort to reduce the weight of the concrete blocks, manufacturers started adding cinders to the cement and water instead of stone. This was a cost-effective way to increase mason productivity by making the blocks lighter.

By using the by-products of coal production, this was one of the first instances of sustainable practices. Later on, volcanic cinders were also introduced as an alternative to stone aggregate.

The practice of adding cinders to concrete continues today. Although, they are not the only lightweight concrete masonry unit available.

Other similarly lower density concrete blocks have been introduced using synthetic aggregates such as expanded polystyrene.

So not all lightweight concrete blocks will be cinder blocks, and you cannot tell a cinder block from a synthetic lightweight block just by looking at it. But to all intents and purposes, they are all concrete blocks.

An important distinction however is the use to which each of these blocks is put. All concrete masonry units used in construction must meet minimum requirements and building codes.

Make sure that the concrete blocks you intend to use are fit for purpose. 

Our question is can you use concrete blocks to build a fire pit, and if so, which ones are the best to use?

Are Cinder Blocks Suitable For Fire Pits?

With the above information in mind, you will now be able to decide if cinder blocks are a good fit for building your fire pit.

Cinder blocks are a non-flammable material, so there is no reason why they cannot be used for this kind of project. 

Perhaps the better question to ask yourself is do you want your fire pit to be a temporary or permanent fixture of your home. This will help you figure out exactly what kind of material you should be using. 

A temporary fire pit can be constructed in a couple of hours as a simple DIY project. If you know you want a more permanent fire pit, then you will need to set aside a weekend to get it built. 

For a temporary fire pit, cinder blocks are absolutely fine to use. You just need to figure out what size you want it to be and calculate the number of blocks needed.

The point of using cinder blocks for a temporary fire pit is that they are not designed to be exposed to high temperatures for long periods of time. A fire that is enclosed in any way is safer, but will also heat up the surrounding materials. 

Over time the cinder blocks may begin to show cracks and there is a danger that under high prolonged heat they could fail and cause injury.

However, if you are only using the fire pit occasionally or for short periods of time, the cinder blocks should last a few years.

If you intend to have a permanent fire pit, then you will need to put more thought into the design and the materials that you are going to use.

While you can still use cinder blocks to create the shape and structure of the fire pit, you will need to line it with a fire rated material.

How Many Cinder Blocks Do I Need?

How Many Cinder Blocks Do I Need?

Once you have decided whether you are having a temporary or permanent fire pit, you can choose a size and design.

This will determine how many cinder blocks you will need. Also take into account how many people will be sitting around the fire pit at any one time.

A circular fire pit that is three feet in diameter is sufficient for 3-4 people. For every additional person you want to accommodate, add one more foot.

Larger designs will need more blocks than smaller, simpler designs, but this depends on the size of the blocks that you are using.

A small, simple and temporary circular fire pit can be made from less than 20 cinder blocks at 8” x 8” x 16” which is the most commonly used.

A square fire pit is potentially much easier to build than a circular one, but will take up more space.

For a temporary fire pit just place a square of blocks on the ground and then add another layer of blocks on top making sure that these span the joints of the blocks below.

For a 3 ft x 3 ft square fire pit, you would need between 24-28 cinder blocks at 8” x 8” x 16”.

You can add concrete cap blocks on top to give it a neater finish, but make sure you don’t make the fire pit too high, or you won’t benefit from the heat it throws out.

How To Build A Fire Pit Out Of Cinder Blocks 

Once you know that a fire pit is allowed, and you have checked the local ordinances, you need to decide where your fire pit is going to be located.

Avoid overhanging branches and make sure the fire pit is at least 20 feet from your house, deck or other flammable structure.

Clear the area where you are building the fire pit. You can put a fire pit directly on dirt, but it’s better to put some kind of fireproof material underneath.

Any grass should be cleared away, and it’s a good idea to dig down a couple of inches to give the blocks a foundation.

For a circular fire pit, mark out the area with string or with spray paint. Place the first block, making sure it is level and stable on the ground.

Add the rest of the blocks so that their corners are touching. Ensure that there is allowance for some airflow.

Then add the second layer of blocks, making sure that they straddle the joints of the blocks below. This makes the structure more stable.

Test the height of the fire pit by sitting on a chair that you intend to use for that purpose. Add or take away a layer accordingly.

A fire pit that is too high will direct all the heat upwards and will not benefit the people sitting around it. If you want to do some cooking on your fire pit, add a grill to the top.

If you enjoy using your temporary fire pit, you could make it permanent by adding fireproof mortar to the blocks.

You should also consider lining a permanent fire pit with metal or fire bricks to make sure that it lasts.

What To Know Before Building A Fire Pit

Before beginning your fire pit project, you will need to check if fire pits are permitted in your neighborhood and if you will need to apply for any permits or meet any regulations.

Your local fire department, municipal office or homeowners association should be able to help.

Regulations can vary by state, city, county or even neighborhood, so make sure you are clear on what is and is not allowed before you proceed.

Aside from locating your fire pit sensibly as previously mentioned, there are two other rules you need to follow.

The material that you burn should not produce toxic gasses or excessive smoke, even paper or magazines can do this.

Clean, dry, split firewood should be all you are burning. The other rule is that a fire pit should be supervised by an adult at all times.

A fire pit is a great addition to your backyard and a welcoming and fun feature. As long as it is done safely and responsibly, you can enjoy being outside even when the weather turns chilly.

It is also a great way to teach young people about the benefits as well as the potential danger of fire. So it serves as a wonderful educational opportunity too.

Having the chance to enjoy your outdoor space is priceless, and with a simple, inexpensive cinder block fire pit you can do that all year round. And don’t forget those marshmallows!

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