What Porosity Means for a Ceramic Tile

Porosity in a tile refers to the proportion of the tile body that consists of open pores or voids rather than solid material. A highly porous tile has a significant network of interconnected spaces throughout its body that can absorb water, oils and other liquids. A low-porosity tile is dense and compact with very few of these spaces, so liquids have nowhere to enter.

Ceramic tiles are made from natural clay fired at relatively moderate temperatures. The firing process partially densifies the clay but does not achieve the full vitrification that happens when porcelain tiles are fired at higher temperatures and greater pressure. The result is a tile body that retains a degree of open porosity. The amount of that porosity varies considerably depending on the clay composition, the firing temperature and the format of the tile, whether wall or floor.

It is important to distinguish between the porosity of the tile body and the behaviour of the tile surface. Most ceramic tiles carry a glaze on their face which is a glass-like coating that is essentially non-porous. Water and most liquids do not penetrate a glazed ceramic tile surface under normal conditions. The porosity of the clay body becomes relevant only when the tile body itself is exposed, at the back, at cut edges, through grout joints or on unglazed ceramic tiles.

The Classification Standard: What BS EN 14411 Tells You

In the UK and across Europe, ceramic tiles are classified under BS EN 14411, which is the standard that governs tile water absorption rates. The standard divides tiles into groups based on how much water they absorb when tested under controlled conditions. A dried tile sample is boiled for two hours, soaked for a further four hours and then weighed. The difference between the dry and saturated weights, expressed as a percentage of the dry weight, is the water absorption figure.

The chart above shows clearly why ceramic wall tiles are not suitable as floor tiles: the standard permits water absorption above 10 percent for wall tile classifications, making those products significantly more porous than floor tiles. Using a wall tile on a floor not only creates a performance risk from water absorption but also means specifying a tile whose breaking strength is rated for vertical rather than load-bearing use.

What High Porosity Actually Causes in Practice

Understanding what high porosity means in theoretical terms is straightforward. Understanding what it causes in a real installation over time is more useful for making good tile decisions.

Does the Glaze Solve the Porosity Problem?

For surface staining and everyday water resistance, yes. The glaze on a glazed ceramic tile creates a non-porous surface layer that prevents liquids from reaching the porous clay body beneath. This is why glazed ceramic tiles are widely and successfully used in bathrooms, kitchens and other wet areas despite the underlying clay body being porous.

Where the glaze does not help is in the situations where the tile body rather than the tile face is the relevant component. The unglazed back of the tile sits against the adhesive and can absorb moisture from that direction. The cut edges of trimmed tiles expose the clay body directly. Micro-fractures in the glaze that develop over years of use in demanding environments can create pathways through which liquids begin to penetrate the surface.

Porosity Risk by Application

To see the full range of ceramic tile options available from our Elstow showroom, including glazed wall tiles, porcelain floor tiles and everything in between, visit our ceramic tiles Elstow page where you can also request samples and a no-obligation quote.

Porcelain vs Ceramic: The Porosity Difference in Numbers

The porosity difference between standard ceramic and porcelain tiles is not a minor variation. It is a fundamental material difference that explains almost every performance gap between the two product categories. Standard ceramic floor tiles absorb between 3 and 10 percent of their weight in water. Standard ceramic wall tiles can absorb more than 10 percent. Porcelain tiles are classified under BS EN 14411 as absorbing less than 0.5 percent. That is a minimum of six times less absorption and often twenty times less or more.

This difference arises from the manufacturing process. Porcelain clay is refined to remove impurities, pressed under significantly higher pressure and fired at temperatures 200 to 400 degrees Celsius higher than standard ceramic. The additional heat and pressure causes the clay particles to melt and fuse together in a process called vitrification, creating a tile body with very few remaining open pores. Standard ceramic firing does not reach the temperatures required for full vitrification, which is why the ceramic body retains its inherent porosity.

For the applications where porosity matters most, particularly outdoor use, wet rooms and areas of sustained water exposure, porcelain is the correct specification. For indoor applications on walls and in lower-moisture environments, glazed ceramic tiles manage their body porosity effectively through the glaze and perform entirely reliably for decades.

For related reading on how ceramic tile porosity affects real-world decisions about sealing, wet room suitability and frost resistance, the Ceramic Tiles Elstow Guide covers each of these topics in detail.