Tile Water Absorption Standard: ANSI A137.1
When you shop for tile, you encounter a long list of specifications: PEI ratings, DCOF values, shade variation codes. Water absorption is one of the most foundational of these numbers. It tells you how much moisture a tile's body will take in, and that single figure has a direct bearing on where the tile can safely be installed.
Water absorption is expressed as a percentage of a tile's dry weight. A tile that absorbs 0.3% of its weight in water behaves very differently from one that absorbs 8%. The denser and less porous the tile body, the lower the absorption rate, and the better the tile performs in wet, high-traffic, or exterior environments.
Understanding how this number is measured, who sets the standard, and what the categories mean gives you a more reliable framework for evaluating tile before you buy.
How Water Absorption Is Measured
The test method used to determine water absorption is standardized under ANSI A137.1, the American National Standard Specifications for Ceramic Tile. The current edition is ANSI A137.1:2022.
ANSI, the American National Standards Institute, is a private, non-profit organization that accredits standards-developing organizations. ANSI does not write tile standards itself. The tile-specific content within A137.1 is developed and maintained by the Tile Council of North America (TCNA), which was established in 1945 as the Tile Council of America and renamed TCNA in 2005 to reflect its expanded membership across North America.
The test involves drying a tile sample to a stable weight, submerging it in water under controlled conditions, then measuring how much water the tile has absorbed. The result, expressed as a percentage, determines which of four absorption categories the tile falls into.
The Four ANSI Water Absorption Categories
Impervious — 0.5% or less
Impervious tile absorbs virtually no water. This category covers most porcelain tile, which is fired at high temperatures using finely ground clay bodies that produce an extremely dense, low-porosity product. Impervious tile is appropriate for wet areas including shower floors and walls, steam rooms, pool surrounds, and exterior applications where freeze-thaw cycles are a concern. It is also the standard for commercial installations subject to regular wet cleaning.
Vitreous — 0.5% to 3%
Vitreous tile is suitable for most floor and wall applications, including areas with moderate moisture exposure. It performs well in bathrooms, kitchens, and laundry rooms where it will not be submerged or exposed to standing water for extended periods. Many porcelain tiles fall into the vitreous range, though the impervious category is generally preferred for wet floors.
Non-Vitreous — greater than 7%
Non-vitreous tile has the highest porosity of the four categories and is limited to interior wall applications. It should not be used on floors and is not suitable for wet environments. Many decorative wall tiles, including certain hand-painted and artisan ceramic tiles, fall into the non-vitreous range. The classification reflects a design-first material rather than a performance tile.
Semi-Vitreous — 3% to 7%
Semi-vitreous tile is intended for interior use only and should be kept away from wet areas. These tiles are not appropriate for shower installations, exterior walls, or any location where sustained moisture contact is likely. In dry interior applications such as feature walls, backsplashes above the waterline, or low-traffic decorative floors, semi-vitreous tile can perform acceptably.
Why Absorption Rate Matters Beyond Moisture
Water absorption affects more than just how a tile handles wet conditions. It also influences:
Freeze-thaw durability.
Water expands when it freezes. A tile with high porosity will absorb more moisture, and if that moisture freezes, the resulting expansion can cause cracking or spalling. Only impervious tile is reliably frost-resistant and appropriate for outdoor use in climates with freezing temperatures.
Stain resistance.
A more porous tile body is more likely to absorb spills, cleaning agents, and grout haze. Impervious and vitreous tiles are significantly easier to maintain in high-use environments.
Grout and installation compatibility.
Higher-absorption tiles may require different mortar and grout specifications. Some porous tiles need to be pre-wetted before installation so they do not pull moisture out of the mortar bed before it has cured. Your tile installer should always reference the TCNA Handbook for the appropriate setting materials for each absorption category.
Choosing the Right Category for Your Project
For most residential floor projects, especially in bathrooms and kitchens, impervious or vitreous tile is the practical choice. If the space will see regular moisture, prioritize impervious. For dry interior floors with lower traffic, vitreous tile covers most needs.
For wall tile in dry locations, the full range of categories is technically available, though impervious and vitreous tiles remain easier to maintain. Non-vitreous tiles work well as accent or decorative elements where aesthetics outweigh performance demands.
Exterior applications require impervious tile without exception. No other category provides the freeze-thaw resistance needed to hold up through seasonal temperature changes.
Frequently Asked Questions about Tile Water Absorption Standard
Water absorption is the percentage of water a tile's body absorbs relative to its dry weight. It is measured under standardized test conditions defined in ANSI A137.1 and indicates how porous the tile body is. Lower absorption means a denser, less porous tile that performs better in wet, exterior, and high-traffic applications.
Porcelain tile is typically classified as impervious, with a water absorption rate of 0.5% or less. Ceramic tile generally falls into the vitreous, semi-vitreous, or non-vitreous categories depending on its body composition and firing temperature. The distinction matters most when selecting tile for wet areas or exterior use.
Semi-vitreous tile should be used with caution in bathrooms. It is appropriate for dry wall applications such as a backsplash or accent area above the waterline, but it is not suitable for shower walls, shower floors, or any surface that will have regular direct water contact. For wet bathroom surfaces, choose impervious or vitreous tile.
Water expands when it freezes. Tile with higher porosity absorbs more ambient moisture, and in freezing temperatures that moisture can expand inside the tile body, causing cracks or surface failure over time. Only impervious tile is classified as frost-resistant and appropriate for exterior use in climates where temperatures drop below freezing.
The classification system is codified in ANSI A137.1, the American National Standard Specifications for Ceramic Tile. The tile-specific content is developed and maintained by the Tile Council of North America (TCNA), which was established in 1945 as the Tile Council of America. ANSI itself approves the standards but does not write them.
About Nova Tile and Stone
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