Fireclay vs Ceramic – What is the difference?

Traditional Fireclay

A little more than a century ago when modern sanitary ware production began Fireclay was the only option available. This can still be seen in some old installations such as urinals and tends to be heavy and coarse. The materials are very refractory, which means they don’t melt during firing. It was difficult to produce and needed to be fired to about 2280 degrees Celsius, which is a huge energy use and at those temperatures the kilns also don’t last long. It had a very coarse grain so needed to be coated with a slurry (called engobe) to smooth it out prior to glazing and firing.

It was not very good finish and had a high-water absorption of around 13% meaning that germs could actually live and breed in the ceramic.

Vitreous China

Vitreous China was developed because of a demand for easier production, reduced costs, better finish and a more sanitary product. It is much finer and whiter using more refined materials and requires no engobe. Its glaze fires with a shiny, smooth, glossy finish making it easy to clean.

In material it is much less refractory, and differs from fireclay, in that there is more glass created within the body during firing that only requires 1200 degrees Celsius. This means it has a very low water absorption (0.5`%) and is therefore much more sanitary. The downside is that glass at high temperatures becomes fluid and therefore more distortion occurs.

Basin Distortion & Interpretation

The Gareth Ashton Basin quality selection standard is 3mm on a product over 400mm long. This calculates out to 0.6% whereas many international standards are 2% or more.

Fine Fire Clay

Fine Fire clay is a more recent development to create straighter and large products. It is a mixture of the materials of Vitreous China and more refined versions of the refractory materials in Fireclay.

Products produced from this material have very straight lines, so it is quite suitable to produce modern square lines. It tends to have a less smooth glossy glaze finish, and as it contains more refractory material less glass is created in the body during firing, so it has a much higher porosity (4- 6%) than Vitreous China. This makes it less sanitary than Vitreous China and as such cannot be used to produce toilets.

Also, because the body is porous it will take up water over time and expand ever so slightly, but as the glaze does not expand it will eventually crack and take on the appearance of old plates. (This is called crazing).