Here’s What Concrete for Fireplace to Use For

Did you know that when concrete mortar is exposed to higher temperatures, its tensile and compressive strengths decrease? With this in mind, identifying appropriate material is critical for beginners and DIYers looking to cut costs on renovations. So, which concrete is best to construct a fireplace?

Concrete for fireplace is made from a mix of high alumina cement and refractory aggregates like crushed bricks, limestone, or slag. Allow for a number of days of drying and curing before exposing it to high heat, and always reinforced the firebox with brick or metal/steel.

This post will go over the benefits of high alumina cement and refractory aggregates for fireplaces. We’ll also go over the qualities of concrete when exposed to high temperatures, as well as some of the advantages and disadvantages of using these materials to build a fireplace.

modern fireplace

For a fireplace, what type of concrete should you use? – diy concrete fireplace

To protect the surface of a fireplace from severe temperatures, use concrete such as Rutland Castable Refractory Cement. High alumina cement (HAC) and sand, which is made up of calcium aluminates, will be used as aggregates. Its toughness makes it perfect for high-heat environments.

Because of its durability and capacity to resist fire, concrete is frequently considered for fireplaces. Concrete mixing for your fireplace is pretty simple, and there is a wealth of material available online to assist you.

However, because concrete changes significantly when exposed to heat (which we’ll discuss later), there is a correct and wrong way to do this.

Cement with a high alumina content

Grinding minerals like lime and chalk produces high alumina cement (also known as calcium aluminum cement). This is ground and heated, then cooled and ground once more.

Because of its great heat resistance, it is frequently employed in chimneys and furnaces, despite its origins in sewers and underwater construction.

Because it is so fine, it must be handled with a mask and safety goggles.

Refractory Cement

Simply put, refractory cement is cement with heat-resistant qualities, such as refractory particles. They are frequently pre-mixed and packed to make them easy for the user to use.

The key component in “heat-resistant concrete,” also known as “high alumina cement,” is high alumina cement, and there are two types to consider:

In areas of extreme heat, such as the hot face of a kiln, high-grade heat-resistant concrete is employed.

In places with less heat, low-grade heat-resistant concrete is utilized.

Refractory Aggregates with High Alumina Cement Concrete

As previously said, sand, crushed bricks, and HAC, such as the Rutland Castable Refractory Cement from, are required to make your fireplace robust and durable.
Though standard cement and mortar would suffice for fillers and even around some of the sides, the firebox needs something extra-durable. The firebox is usually made of brick or metal to provide long-term endurance. You still need the added protection of putting concrete with refractory aggregates behind and around this.

Is it possible for concrete to explode in a fireplace?

When concrete is exposed to extremely high heat, it can explode. A concrete slab was heated to roughly 600ºC  (1,112ºF) in a recent Empa study, and it exploded due to a severe loss of strength. Because most fires reach such high temperatures, it’s important to strengthen the materials for further protection.

Concrete is made out of sand, cement, and water, and it is reinforced to improve its performance in major construction projects like skyscrapers and bridges.

Unfortunately, according to a study published in the Cement and Concrete Research Journal, concrete explodes due to the same features that make it strong: a lack of pores.

These small pores prevent moisture and steam from escaping, allowing concrete pressure to build up easily. Parts of the concrete blow away as a result of the increased pressure, which some refer to as an explosion.

How to Protect Your Fireplace from High Heat

Heat-resistant refractory concrete can withstand intense temperatures and, as the name implies, can be utilized for hot-face applications. The surface of a hot-face application is in direct contact with the principal source of heat.

To ensure a durable and robust fireplace, I recommend mixing heat-resistant cement with your concrete, such as Meeco’s Red Devil Furnace Cement from This substance will safeguard your fireplace up to 2,000 degrees Fahrenheit (1093.33 degrees Celsius), which is far higher than normal fire burns.

fireplace inside the room

Concrete Properties at High Temperatures

Concrete’s mechanical qualities deteriorate at temperatures above 300°C (572°F). The following features are responsible for the durability and reliability of concrete used in a fireplace:

Tensile strength
Compressive strength

Let’s take a deeper look at each of them in the sections below.

Compressive Strength

Concrete’s compressive strength refers to how much weight or pressure it can withstand. To put it into perspective, it is determined by “pressing together” the concrete, which is usually accomplished by placing a large weight on top.

As the temperature rises, so does the compressive strength of concrete. Concrete loses moisture content when it heats up owing to evaporation, therefore the proportions of the mixture and the type of particles have an impact on the strength of heated concrete.

Due to the amount of water utilized, compressive strength is reduced less in lean concrete (liquid and pourable) with a low cement percentage. When the compressive forces that keep concrete together weaken, it becomes vulnerable to cracks and even explosions.

Tensile Strength

The ability of concrete to resist cracking under tension is referred to as its tensile strength. Unlike compressive strength, which determines the strength of concrete when it is “pressed together,” tensile strength determines the strength of concrete when it is “pulled apart.”

However, just like the compressive strength of concrete, the tensile strength of concrete diminishes as the temperature rises.


At low-stress levels, the stiffness of concrete is frequently constant. It does, however, decrease when the temperature rises and stress levels rise.

Concrete has a low coefficient of thermal expansivity, which refers to the tendency of matter to change shape, volume, or area in reaction to changes in temperature. To avoid cracking, concrete should be built with provisions for expansion.


Steel-reinforced concrete is prone to spall. Spalling is defined as little pieces of material flaking away from the main body. It typically occurs when steel rebars rust.

When concrete is heated quickly and the steam produced by the moisture inside cannot escape quickly enough, pressure forms beneath the surface. Spalling will occur when the pressure rises, and it can be highly dangerous.

Spalling is more likely to occur at high temperatures, as is the case with each of these features. However, this may be the one to look out for in a fireplace, as the area is unlikely to be “pressed” or “pulled.” Instead, problems with moisture and pressure from within are more common.

Concrete Fireplace Benefits

Concrete has grown in popularity as a material for fireplaces, countertops, roofing, floors, and sinks over the years. It’s highly adaptable, and it’s one of the DIYer’s first choices for building fireplaces.

If properly cared for, it is both durable and long-lasting.

When combined with elaborate designs, it can boost the value of your home.
Because the block absorbs and then redistributes any heat created, it can improve the heating efficiency of your home.

Concrete Fireplaces’ Drawbacks

Concrete fireplaces, as popular as they are, may be harmful under the wrong circumstances, as we’ve already demonstrated. It’s more probable that anything will go wrong if it’s not done by professionals because many DIYers use cheaper materials and don’t always know how to assure safety.

Because they require a foundation and are sometimes heavy, concrete fireplaces are difficult and expensive to install.
Because they require clearance from combustible materials, they take up a lot of space in a room.
They aren’t good for the environment.

How to Care for a Concrete Fireplace

Even the nicest fireplaces can crack and deteriorate if they are not properly maintained. Your fireplace and chimneys should be inspected at least once a year to maintain your home’s safety. These inspections will ensure that you have the necessary clearances, that the structure is sound, and that deposits are not present.

The good news is that keeping your fireplace in good working order is simple. Here are some easy steps to follow:

Make sure you’re using the right kind of wood.
Install carbon monoxide and smoke alarms.
Keep an eye out for creosote and soot build-up.
Concrete fireplaces, on the other hand, are low-maintenance and long-lasting.

Last Thoughts

Concrete may be utilized to beautify both indoors and outdoors if it is chosen with design in mind. Because of its durability, it is a versatile and popular choice.

You should be able to create a gorgeous, safe, and conversation-inspiring fireplace if you take the appropriate precautions and reinforce your concrete with high alumina cement and refractory aggregates.


What other type of cement is used for concrete fireplaces?

QUIKAIRE® Fireplace Mortar (No. 88620-21) consists of silate-containing reinforced cement caulk used to seal and repair broken or chipped wood tucks in masonry and fireplaces.

tag: diy concrete fireplace makeover, seams, budget-friendly, affiliate links, attaching the cement board, 09 pm

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