What Kind Of Brick Do You Use For A Fireplace?
When constructing a fireplace, choosing the right type of brick is one of the most important decisions. The bricks must be able to withstand extremely high temperatures without cracking or breaking down over time. There are several options to consider when selecting bricks for a fireplace, each with their own advantages and best use cases.
The main types of bricks used for fireplaces include fire bricks (also called refractory bricks), clay bricks, castable refractory, soapstone, and common bricks. Fire bricks are designed specifically to endure intense heat, while clay bricks provide an attractive look. Castable refractory is an extremely heat resistant concrete-like material used as an alternative to bricks. Soapstone is a natural stone valued for its high heat retention. Common bricks are cheaper but may not withstand heat as well.
In this article, we will explore the properties and best uses of each type of brick to help you choose the right option for your fireplace.
Fire Bricks
Fire bricks, also known as refractory bricks, are a type of brick made from refractory ceramic material that can withstand extremely high temperatures, typically above 1000°C (wikipedia.org/wiki/Firebrick). They have special properties that make them suitable for lining fireplaces, ovens, and furnaces.
Some key properties of fire bricks that make them ideal for high heat applications are:
High heat tolerance – Fire bricks are designed to withstand continuous exposure to temperatures above 1000°C without decomposing or cracking. Their chemical composition and porous structure gives them a high melting point. This allows them to stand up to the intense heat of a fire or furnace (https://theconstructor.org/building/fire-bricks-properties-types-uses/29377/).
Low thermal conductivity – Fire bricks have low thermal conductivity, meaning they do not allow heat to pass through them quickly. This keeps the heat contained in high temperature areas like fireboxes, and protects the surrounding structure from damage. The porous nature and limited conductivity prevents rapid heat transfer (https://theconstructor.org/building/fire-bricks-properties-types-uses/29377/).
Refractory Bricks
Refractory bricks are specifically designed to withstand extremely high temperatures and are commonly used to line fireplaces, fire pits, kilns, and furnaces. They are made from fire clay or other refractory ceramics that can resist heat above 1000°F.
Refractory bricks have a higher alumina content than typical clay bricks, ranging from 30% to 90% alumina. The high alumina content gives them superior resistance to heat. They are very dense and non-porous, which prevents heat transfer. Their low porosity also makes them resistant to corrosion from ashes, chemicals, and slag.
Common types of refractory bricks include fire bricks, high alumina bricks containing over 50% alumina, and insulating fire bricks which have lower density and heat conductivity. The strengths of refractory bricks include:
– High refractoriness to withstand flames, heat radiation, and contact heat
– Good load bearing strength at high temperatures
– Excellent thermal shock resistance
– High erosion and spalling resistance
When selecting refractory bricks for a fireplace, factors like the operating temperature range, physical stresses, and environment need to be considered to find the optimal balance of properties. Properly installed refractory brick fireplace lining can last for decades.
Clay Bricks
Clay bricks are one of the most traditional materials used for building fireplaces. They have been used for centuries to construct fireplaces and chimneys due to their durability and heat resistance properties. However, regular clay bricks do have some drawbacks when used in fireplace construction.
The main issue with using standard clay bricks for a fireplace is that they are prone to cracking and spalling when exposed to high heat over time. Unlike firebricks which are designed to withstand extremely high temperatures, regular clay bricks are only fired during initial manufacturing to around 1000-1250°F. This makes them susceptible to damage as fireplace temperatures can routinely exceed 2000°F.
As the clay bricks heat and cool during fireplace use, they expand and contract. This puts stress on the brick that can cause cracks and fragments to break off (spalling). Once damaged, it accelerates deterioration of the bricks and compromises the integrity and safety of the fireplace structure.
While clay bricks lend a classic look, fireclay bricks are a better choice for fireplace construction. Fireclay bricks are fired at much higher temperatures so they can endure repeated heating cycles without cracking or spalling.
Castable Refractory
Castable refractory is a cement-like material that is used for fireplaces and high heat applications up to 3000 degrees Fahrenheit. It is made of calcium aluminate cement and high alumina content, giving it superior heat resistance compared to other materials like clay bricks. Castable refractory can be molded and shaped when wet, then sets very hard once dry and cured, similar to concrete. It is installed monolithically, meaning it is cast all at once into the entire shape needed, as opposed to individual bricks.
According to Rutland’s website, their Castable Refractory Cement “chemically sets and dries as hard as brick” with strengths over 5000 psi, far exceeding the requirements for firebrick. This makes it an ideal cement for fireplaces and wood stoves. It can be used to make custom shapes and sizes for the firebox, and provides excellent protection from heat. My Material Warehouse’s Heat Cast 40 is formulated specifically for high temperature applications up to 3000°F.
Soapstone
Soapstone is a natural stone material that has been used for centuries in wood-burning fireplaces and stoves. It is praised for its ability to absorb, store, and slowly radiate heat over long periods of time. According to Four Reasons Why Soapstone Stoves are Worth the Investment, the dense nature of soapstone allows it to soak up heat from the fire like a “thermal battery.” The stored heat is then gradually released into the room, helping maintain comfortable temperatures long after the fire has gone out.
The density and thermal properties of soapstone make it an excellent material for fireplace and stove surrounds. Soapstone is non-combustible and can withstand extremely high temperatures. It’s also a poor conductor, meaning the exterior surface stays relatively cool to the touch while the interior absorbs heat from the fire. According to some enthusiasts, soapstone stoves provide a gentle, even heat perfect for whole home heating.
On the downside, soapstone can be quite heavy and requires extra structural support. It’s also more expensive than some alternative natural stone or masonry options. Overall, soapstone remains a classic, time-tested material appreciated by many seeking the comfort and old world charm of a masonry fireplace or stove.
Common Brick
Common brick, also known as face brick, is one of the least expensive options for brick fireplaces. It is mass-produced for typical masonry and construction projects, not for high heat applications like fireplaces. Common brick is made from clay and fired at lower temperatures than firebrick, so it cannot withstand the intense heat of a fire over time. Using common brick in a fireplace is not recommended because it can crack or break down after repeated heating and cooling cycles (https://sdinspect.com/blog/fireplace/). The cracks allow heat and embers to pass through to the structure behind the fireplace, creating a potential fire hazard. For these reasons, common brick should be avoided for fireplaces despite its lower cost and wider availability.
Choosing Brick Type
When choosing brick for a fireplace, there are four key factors to consider:
Heat Rating
Some bricks, like fire bricks, are specifically designed to withstand high heat. According to this source, fire bricks can resist temperatures up to 2,800°F. Refractory bricks are another good option for heat resistance.
Durability
Bricks like fire bricks and refractory bricks tend to be very durable and resistant to cracking or crumbling over time. According to this source, clay bricks may be less durable in a fireplace setting.
Aesthetics
For appearance, burnt clay bricks or concrete bricks often look most attractive around a fireplace. Their color and texture can complement traditional fireplace designs.
Cost
Common bricks tend to be the most affordable option, while specialized fire bricks cost more. Refractory bricks also tend to cost more than basic clay bricks.
Brick Installation
Proper installation is critical for a safe and functional brick fireplace. The mortar used to adhere the bricks is an important consideration. Traditional mortar mixes include Type N, Type S, and Type M, with Type N commonly used for firebrick installation since it withstands high temperatures. Insulative mortars like refractory mortar provide extra protection. When laying bricks,spread a layer of mortar on the back of each brick and press firmly into place.
Insulation between the firebox and surround is also key. Fibrous blankets or boards help prevent heat transfer to the surrounding structure. An air gap of 1-2 inches provides further insulation. Proper ventilation with outside air intake allows for good airflow. This removes smoke and prevents gases from accumulating in the home. Builders must closely follow fireplace construction codes for clearance to combustibles to prevent safety hazards.
Conclusion
In summary, the best bricks for fireplaces are fire bricks, refractory bricks, and clay bricks. Fire bricks are specifically designed for fireplace and chimney construction. They can withstand extremely high temperatures and thermal shock. Refractory bricks are similar to firebricks but are more porous. While they work well for fireplaces, they may need to be sealed or glazed. Clay bricks also withstand high heat and are an attractive, classic choice for fireplaces. Other options like castable refractory, soapstone, and common brick have drawbacks in terms of heat tolerance, durability, or aesthetics.
When selecting bricks, consider the design, exposure to heat and flames, durability needed, and aesthetic preferences. Proper brick installation using mortar and following building codes is also critical for safety and longevity. With the right bricks and masonry techniques, you can build a beautiful, long-lasting fireplace as a focal point in your home.
