Shining the Light on Water Absorption and How Levels Impact Tile Quality

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Any tile with a water absorption rate above 0.5% is classified as ceramic, not porcelain, Unfortunately there are increasing instances of inferior, high absorption tiles used in flooring across New Zealand which can compromise longevity and durability.

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What is the difference?

Porcelain tiles are defined by their low water absorption (≤0.5%),whereas most ceramic tiles absorb significantly more moisture, making them less durable, more prone to staining, and more vulnerable to long-term wear when used on floors.

'Porcelain' tile refers to a measured average water absorption across 4 - 6 samples of 0.5% or less (this is a minimum standard, and many porcelains are up to 10 times lower).

Ceramic tile has a water absorption at higher levels above 0.5%.

The superior lower water absorption of porcelain tile is a result of vitrification that happens when pressed clays, silica and feldspars are fired under intense temperatures of 1200 - 1300 degrees creating an inert, stable and highly durable tile.

Vitrification in tiles refers to a manufacturing process that creates a dense, glass-like surface, resulting in tiles that are durable, low in porosity, and resistant to stains and moisture.

The tile industry moved to porcelain production for floors in the 1990s starting with Italian manufacturers. Chinese and other Asian producers soon followed converting to porcelain. With this industry move, porcelain is still recognised internationally as the standard required for all floors internally. Porcelain floor tiles have significant longevity and performance benefits over ceramic tiles, especially in areas prone to moisture such as bathrooms, laundries and kitchens.

Why tiles are not all created equal: the firing process

In a market where there is often a focus to buy and purchase at cheaper rates, combined with limited understanding of potential issues by some importers, customers are at risk of unknowingly compromising the quality and longevity and performance of tile flooring.

When tiles are not fired at 1200 to 1300 degrees and are not in the Kiln for at least 35 to 45 minutes, an inferior product is produced. Some tiles on the New Zealand market currently have had firing time significantly reduced to only 25 to 30 minutes and possibly at lower temperatures, producing a compromised less dense material that has not been vitrified to an inert state (see above).

Most designers, if made aware of the difference between ceramics and porcelain and what the implications can be, will steer away from the underfired 1 to 3% material for the following key reasons:

Possible effects of higher water absorption tiles:

Higher water retention and spore and microbial/mould growth in wet area floors and shower enclosures
Increased absorption will reduce grout life due to the increased retention of water
Higher incidence of defective pieces in boxes
Post-production warping
Lower glaze hardness (PEI ratings)
Reduced warranties from manufacturers
Possible reduction in engobe which, with increased water absorption, can cause water marking and worse, staining
You cannot use 1 to 3% water absorption products externally in New Zealand
Longevity of the tile and system will be reduced compared to a porcelain.

Select true porcelain to minimise risk

Ultimately, with over 20% of floor tiles imported from China classified as ceramic rather than true porcelain, a clear understanding of water absorption thresholds is critical at specification stage. Differentiating between ceramic, standard porcelain (≤0.5%), and ultra-low absorption porcelain (≤0.1%) reduces risk in wet and high-traffic environments, supports long-term performance, and helps ensure specified materials meet durability, compliance, and lifecycle expectations over the full service life of the building.