Is Clay Flammable?

In this article, we will evaluate the following question: “Is Clay Flammable?”, as well as other important subjects regarding many types of Clay materials such as modeling, raw, and air-dry clay.

Is Clay Flammable?

Overall clay cannot ignite, but it depends. There are many materials that are clay-composed, and people can use the word with different meanings. Normally, clay does not possess combustible materials within, but that’s only part of the story.

What is clay

Clay is part of the soil. Is a mix of minerals, rocks, sand, and sediments.

Clay is basically mud, it can be used as a synonym, but mud is usually formed by the top soil while clay is a mineral from within.

There are many types of raw clay, their source is what dictates its characteristics.

Where does it come from?

Clay comes from the soil. But how and where does soil come from?

Weathering is the driving force that allows soil and clay to exist. 

Over the millennia, wind, rain, running water, seismic activity, and all forms of life had slowly scratched the earth’s surface, allowing small dust particles of many kinds to assemble.

The particles then settled in a thin brownish layer, usually no longer than 1 meter. This is what we call soil.

To understand more of what soil and clay are we must look deeper into how weathering and life shaped our planet. This is a process we call pedogenesis. 

The soil formation process

If you ever tried to find information on where soil and clay came from, we bet it was not easy. In fact, it is not so ordinary to understand these processes but we will do our best to simplify them.

The mineral part of the soil is formed by physical and mechanical disintegration of the rocks that are close by (we call them parent rocks), and through chemical processes that happen after.

The surface of the ground suffers more from weathering and other forms of stress. The formation of the soil starts from the top. 

If we (literally) dig deeper into the soil we would see different sheets, we call them Horizons. They are the result of millions of years of complex events. 

Soil Horizons example.


As you can see from the picture above, the process of soil formation is intimately related to life itself. 

Plant roots have the very important task of slowly breaking down the parent material, shattering them into smaller pieces, and allowing water to infiltrate and promulgate this even more.

Therefore, not only will the original rocks play an important role in soil and clay formation, but the plants in a certain region too. But life also depends on the soil, so it’s a never-ending cycle.

Horizon O is where almost all of human life is settled.

All of our agriculture takes place in this same part.

The most important chemical process in pedogenesis is the formation of clay.

After various erosion agents take place, especially in humid environments, chemical weathering gives rise to many compounds that will compose clay.

We point out: 

  • The permanence of soluble materials like carbonates, bicarbonates, and silica;
  • The apparition of colloidal gels made of free heavy cations of aluminum and iron;
  • And microcrystalline sheet-like structures that can fix iron and aluminum hydroxides to their surface.

Geochemical and biochemical weathering are the most important precursors of clay formation, especially in the presence of water. 

The first is a characteristic of tropical climates. Can liberate completely the mineral constituents (silica, aluminum, and bases) into the soil.

The second, although, is characteristic of temperate climates where conditions are softer, so some microscopic crystalline particles remain undamaged.

This all, combined with specific local factors will determine what clay will look like.

Clays can be grouped according to their characteristics. Here are some examples:

  • Kaolinite.
  • Montmorillonite/ Smectite.
  • Illite.
  • Chlorite.
  • Vermiculite.


Clay has been used by humanity for handicraft and sculpting for at least 30.000 years, 18 thousand years before humans started farming.

Due to its malleability, clay has been used for many artistic and cultural purposes. Humanity has always been about expressing themselves, and will probably keep doing so.


Clay can be used directly with natural building techniques such as adobe, cob, and cordwood.

It can be used to compose plaster, floors, paints and as a precursor for many ceramic building materials.

There are studies showing that nanoparticles of clay can be used as an additive for construction materials, acting like a fire-retardant.


Clay is still a popular compound in DIY projects.

Some clays require heat to harden, some only require drying.

Here are some examples of sculpting clay products and characteristics:

  • Ball Clay: a sedimentary clay mixed with other types of clay. Has a pale gray color.
  • Earthenware Clay: Used to create pottery and sculptures.
  • Fire Clay: will only harden after a very intense heat.
  • Kaolin Clay: used mostly in the production of porcelain. The color is very pale once it hardens.
  • Stoneware Clay: requires an even larger temperature than earthenware. It’s used in front yard landscaping.
  • Dough Clay: it doesn’t actually have clay as one of its constituents. Play-Doh is probably the most common product.
  • Polymer clay: this is used by many professionals and enthusiasts. You can bake polymer clay at 275°F for about 30 minutes per 1/4 inch of thickness.
  • Paper clay: paper is added to it to help bind the clay together.
  • Water-based clay: is considered cheaper, and dries out quickly

Other uses

Uses are countless. Let’s cite some:

  • Ceramics;
  • Refractory materials;
  • Ballistic materials;
  • Medical implants;
  • High-tech electronics;
  • Clay water filters;
  • Kitchen utensils.

Clay chemistry and properties

Clay is a very versatile material. This is because its chemical properties are very unique and complex.

As explained before in this article, clay is composed mainly of minerals. But unlike other minerals like rocks and carbonates, it’s soft. This happens because of its complex chemistry and the water content within.

Clay components, structure, chemistry, and effects are so wide that there’s no specific nomenclature to be followed. 

When dealing with specific scientific questions regarding clay materials, each material must have its clay mineral constituents and origin detailed, so only then the subject can be studied.

The chemistry of synthetic clays and clay-like compounds will not be explained in this article. Only a general explanation will be provided.

If we looked close to clays we’d see macrocrystalline forms. Geometrical structures composed of silica and aluminum compounds, highly bonded with oxygen and other ligands, in sheet forms.

But the sheets are interleaved with another layer composed of water and ions, which allows malleability. As a result, clay resembles a lot like quicksand.


As you can see from the picture, when clay dries the water leaves, so its properties change, and hardness arises.

But when it’s fired above 1000°C, the silica components react with each other and new chemical bonds are formed. The result is a very hard and cohesive compound.

Clay flammability

It is not safe to assume that any form of clay will ever ignite or catch fire, but the fire hazard is practically unreal.

You have to put clay under a lot of heat to alternate its characteristics.

Clay is an inorganic compound, it’s made of minerals and can’t ignite. The only things that can catch fire are organic compounds.

But it doesn’t mean that nothing will occur if clay is tossed in the fire. 

Burning some forms of clay is required to give birth to porcelain, pottery, some construction materials, and many other things.

But if in a material clay is only one of the constituents, we can’t assume it’s safe to burn it, but most materials will be. Check the FAQS section below for a more specific explanation of common clay materials.


Many materials are named clay. It is not flammable in its raw form. Clay is considered a fire retardant material for many purposes.

Frequently Asked Questions (FAQS): Is Clay Flammable?

Can air-drying clay catch on fire?

It’s not likely that it will. But if you add flammable components to it like certain paints, it might. Also, it will start crumbling out after intense heating or in an open fire. It shouldn’t be put in a kiln.

Is air dry clay heat safe?

It can resist some heating, but not much (about 76°C/170°F).

If you heat it too intensively, put it on a kiln or microwave, it will crack and become unusable. It’s unlikely that it will start a fire but can still heat and harm you.

Can you make an ashtray out of air-drying clay?

Air drying clay can’t go in direct contact with heat. If you wish to make an ashtray using it, you will need to assemble another kind of fire-proof material on top, in a way

Is clay safe for candles?

Yes, but only if another fire-proof material is added so the clay doesn’t get in direct contact with the fire or heating. Clay can’t normally burn but it can crack under intense heat or temperature variation.

Is modeling clay flammable?

It depends. There are many kinds of modeling clays, and not all of them are actually made of clay.

Normally they can’t catch fire. Some of them must be fired so hardness occurs, some are hardened in the air and can’t be heated. But all of them can heat and burn you because of that, so the best is to follow label instructions if applicable.


DUCHAUFOUR, R. Pedology: pedogenesis and classification. Springer Science & Business Media, 2012.

Bergaya, F., & Lagaly, G. (2006). Chapter 1 General Introduction: Clays, Clay Minerals, and Clay Science. Handbook of Clay Science, 1–18. doi:10.1016/s1572-4352(05)01001-9

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