What Materials Do You Need To Build A Kiln?

A kiln is a thermally insulated chamber used for the firing of materials such as clay, glass, ceramics and metal in the making of objects such as pottery, bricks, and tiles. The purpose of a kiln is to bring materials to high temperatures for hardening, drying, setting or fusing while providing a controlled atmosphere. Kilns have been used for millennia to turn clay and other materials into useful and decorative objects.

The earliest kilns were pit kilns, which were holes dug in the ground and used for firing pottery and metalwork. Over time, technology improved and kilns have evolved into more complex electric and gas-fired kilns used today. The most common types of kilns used by modern potters and ceramicists include:

• Electric kilns – The heating elements are electric coils.
• Gas kilns – The heating elements are fueled by natural gas or propane.
• Wood-fired kilns – Burning wood provides the heat for firing.
• Raku kilns – Small, portable kilns used for raku firing.

When selecting a kiln, factors like the size, energy source, and desired temperature range help determine the best type for a given application.

Refractory Bricks

Refractory bricks are a crucial material for building a kiln. They are designed to withstand extremely high temperatures from the heating elements inside the kiln. Refractory bricks have high heat capacity, which means they can absorb and store large amounts of heat energy.

There are several types of refractory bricks to choose from when building a kiln:

• Fireclay bricks – These are made of at least 30% alumina and are resistant to temperatures up to 1,800°F. They are a common choice for kiln construction.
• High alumina bricks – With over 45% alumina content, these can withstand temperatures up to 3,000°F. They are more expensive but have increased durability.
• Silica bricks – Made of at least 93% silica, these bricks work well for temperatures up to 3,000°F. However, they are prone to thermal shock.
• Insulating firebricks – Lightweight and porous, these provide insulation and can resist temperatures up to 2,800°F.

Choosing the right type of refractory brick is crucial for creating a kiln that can reach and maintain the high temperatures needed for firing clay and other materials. The quality and thickness of the bricks will impact performance and durability.

Insulation

Insulation plays a critical role in kiln design and performance. It helps retain heat and maintain even temperatures throughout the firing chamber. Without proper insulation, a kiln would require much more energy to reach and sustain target temperatures. Insulation also protects the outer shell from high internal temperatures.

There are several types of insulation used in kiln construction:

Ceramic Fiber – This is a lightweight, flexible material made from high-purity alumino-silicate fibers. It can withstand temperatures up to 2300°F. Ceramic fiber comes in blankets, boards, and vacuum-formed shapes to fit various kiln designs.

Firebrick – Standard refractory firebricks provide insulation value in addition to their structural properties. Using multiple layers of firebrick can create an insulated wall in a kiln.

Perlite – This is a volcanic glass expanded with heat to form lightweight granules. It is mixed with binders to create an insulating concrete or plaster for kiln interiors.

The type and amount of insulation will depend on factors like the kiln’s operating temperatures, energy efficiency goals, size and wall thickness. A sufficient insulation layer helps create the conditions for even, efficient firing cycles.

Heating Elements

When building a kiln, one of the most important considerations is what type of heating element to use. Kilns can be fired using electricity, gas, or wood. Electric kilns are the most common for hobbyists and small studios because they are convenient, consistent, and easier to control than gas or wood. The main options for electric heating elements are:

Nichrome Wire

Nichrome is an alloy of nickel, chromium, and often iron that resistors heat when electricity passes through it. Nichrome wire coils are a simple and inexpensive heating element. They can easily be wrapped around ceramic posts in various configurations to distribute heat. However, they are less durable than other options.

Kanthal Wire

Kanthal wire is a ferritic alloy that performs better than nichrome at high temperatures. It holds its shape and strength better when glowing red hot. Kanthal wire coils tend to last longer than nichrome.

Ceramic Fiber

Ceramic fiber cores wrapped in a metal coil or foil can withstand very high temperatures. They radiate heat more evenly than wire alone. Ceramic fiber elements are rigid and durable. They are more expensive but can greatly outlast wire.

The heating elements significantly influence the performance, durability, and efficiency of an electric kiln. Carefully researching the options before building a kiln allows selecting elements that suit the budget and needs of the project.

Kiln Shelves

Kiln shelves separate ware from the floor of the kiln and support pottery as it is being fired. The shelf material needs to withstand high temperatures without warping or expanding. Ceramic shelves are the most popular option.

Ceramic shelves are made from ceramic materials that can handle the high temperatures inside a kiln without cracking or sagging. Cordierite is the most common material used for ceramic shelves. It has a low coefficient of expansion, meaning it resists expanding and contracting during the extreme temperature changes inside a kiln. This makes it an ideal shelf material.

Cordierite shelves come in various sizes and thicknesses. Thicker shelves are more durable and hold heavier loads. The size of shelf needed depends on the kiln dimensions and the types of pieces being fired. Small shelves allow flexible shelf stacking while larger shelves hold more pieces. Most ceramic shelves have small half-circle cutouts that allow heat circulation. Multiple shelves stack inside the kiln to fully utilize the space.

Stand/Frame

One of the essential parts of building a kiln is constructing a proper stand or frame to provide structure and support. The frame holds up the kiln chamber and ensures stability while firing. Most kiln frames are made from welded steel, which provides strength to withstand high temperatures without warping or sagging over time.

When designing a kiln frame, considerations include weight capacity, size of the kiln chamber, and portability if needed. The stand must be able to safely hold the weight of firebricks, insulation, and other kiln components. Steel tubing, angle iron, or channel can be cut and welded together to form a sturdy base. The frame also elevates the kiln off the ground for better air circulation and ventilation underneath.

In addition to structural steel, other framing options include heavy gauge wire shelving, tubular steel furniture frames, or cement blocks. Portable and mini-kilns may sit atop a wire stand or steel table legs. The frame configuration depends on individual kiln design, permanent versus movable setup, and weight of the materials. Properly constructing the stand is key to building a secure and long-lasting kiln.

Ventilation

Proper ventilation is critical for a well-functioning kiln. The purpose of ventilation is to control airflow and allow oxygen into the kiln to aid in complete combustion of the fuel. Good airflow also ensures even heat distribution and helps expel harmful fumes. There are several components that facilitate effective ventilation:

Peepholes – Small openings in the kiln wall that allow a view inside the kiln to monitor the progress of firing. Peepholes also allow some air intake.

Dampers – Adjustable metal plates that regulate airflow into and out of the kiln. Proper damper use controls oxygen flow for clean, efficient firings.

Chimney – The exhaust flue at the top of the kiln that allows hot air and gases to escape, creating natural draft through the kiln. The chimney’s diameter and height impacts the strength of the draft.

With the right ventilation components properly adjusted, oxygen can flow through the kiln, fuel can burn completely, fumes can escape, and the ware can fire evenly – all critical aspects of a successful firing.

Wiring and Controls

For electric kilns, proper wiring and controls are essential for safe and effective firing. Here are some key considerations:

The kiln should be wired to meet electrical code requirements based on the kiln’s power needs. Consult an electrician to ensure proper wire gauge, circuit breakers, and connections. The wiring needs to safely handle the kiln’s electrical load.

Invest in a programmable controller to allow custom firing profiles. Many controllers allow you to program ramp rates, target temperatures, and hold times. This level of control is important for consistent results. Popular controllers include Bartlett, Skutt, and Paragon.

Choose a controller with ramp/hold programming and multiple programs. Look for features like delay start, alarm warnings, and error codes. Make sure it can accommodate the number of thermocouples needed for your kiln.

Place thermocouples properly to allow the controller to regulate temperatures accurately. On most electric kilns, at least two thermocouples are recommended.

Get a back-up adjustable high limit control for overfire protection. If anything goes wrong with the digital controller, the back-up will shut the kiln off at a preset temperature.

Install all controls and wiring per manufacturer recommendations. Pay close attention to technical specifications and wiring diagrams.

Safety Equipment

Proper safety equipment is crucial when operating a kiln due to the extreme temperatures involved. Severe burns or other injuries can result if precautions are not taken.

Heat-resistant gloves, such as leather or specially coated gloves, are a must when loading and unloading the kiln. Normal fabric gloves will not withstand kiln temperatures. Safety glasses or goggles should also be worn to protect eyes from infrared heat and dust.

An apron made of leather or fire-resistant materials provides protection when standing near the opening of the kiln. Sturdy closed-toe shoes are also recommended when firing a kiln.

A respirator or dust mask should be used if the kiln produces dust or fumes during firing. Proper ventilation of the kiln room is also important.

Having the proper safety gear on hand ensures firing the kiln can be done comfortably and injury-free. Never take shortcuts when it comes to protecting yourself around extreme heat.

Additional Accessories

Though not entirely necessary, there are some useful accessories that can enhance your kiln experience.

Kiln wash is a protective coating that can be applied to kiln shelves, posts, and the interior kiln walls. It helps prevent materials from sticking during the firing process. Choose a kiln wash made specifically for your kiln’s temperature range.

Kiln furniture refers to posts, props, stilts, and saggars used to elevate and support artwork in the kiln. These accessories allow ample airflow and prevent contact between pieces. Kiln furniture is typically made from ceramic or refractory materials.

A pyrometer is a thermocouple device used to accurately measure kiln temperatures. While most kilns have a built-in thermocouple, a pyrometer can give you a secondary reference point. A pyrometer with a chart or graph feature allows you to visualize the firing curve.