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. Water absorption is an important consideration for wet or exterior environments, but the product's approved applications and other performance classifications must also be checked.
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, accredits standards-developing organizations and approves American National Standards. ANSI A137.1 is developed and periodically revised by the ANSI Accredited Standards Committee A108, for which the Tile Council of North America serves as secretariat.
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 has a water absorption rate of 0.5% or less. This category includes porcelain tile, which is defined as impervious tile under industry standards. Its dense, low-porosity body makes it suitable for consideration in wet and exterior environments. However, suitability for shower floors, steam rooms, pool areas, exterior installations, or commercial applications must be confirmed for the specific product, including its slip-resistance and product-use classifications.
Vitreous — 0.5% to 3%
Vitreous tile has a water absorption rate between 0.5% and 3%. Depending on the product's approved applications, it may be suitable for many interior floor and wall installations, including kitchens, bathrooms, and laundry rooms. For surfaces exposed to regular moisture or standing water, review the manufacturer's technical specifications before selection.
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 has a water absorption rate between 3% and 7% and is generally considered for interior applications. It may be suitable for dry walls, backsplashes, accent areas, or certain floors when approved by the manufacturer. Check the product's technical specifications before using it in showers, exterior areas, or locations exposed to regular moisture.
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 higher porosity can absorb more moisture, which may increase the risk of cracking or spalling during freeze-thaw cycles. For exterior installations in freezing climates, confirm that the specific product is approved and tested for the expected freeze-thaw exposure.
Stain resistance.
Water absorption can influence how the tile body responds to moisture and staining. However, cleanability also depends on the surface finish, glaze, texture, grout, and maintenance requirements of the specific product.
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
Water absorption is one factor to consider when selecting tile for residential floors, walls, bathrooms, kitchens, and other moisture-prone areas. A lower absorption rate indicates a denser and less porous tile body, but it does not determine every aspect of product performance.
For dry interior wall applications, products from different absorption categories may be suitable when approved by the manufacturer. Floor applications require tile specifically rated for floor use, while wet floors also require appropriate slip-resistance and product-use classifications.
For exterior installations, select a product specifically approved for the intended application, local climate, and expected freeze-thaw exposure. Water absorption alone does not confirm exterior suitability.
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 indicates a denser, less porous tile body, but the product's approved applications and other performance classifications must also be considered.
Porcelain tile is defined as impervious tile with a water absorption rate of 0.5% or less. Other ceramic tile may fall into the vitreous, semi-vitreous, or non-vitreous categories, depending on its measured water absorption. The specific product's approved applications should also be reviewed when selecting tile for wet or exterior environments.
Semi-vitreous tile has a water absorption rate between 3% and 7% and is generally considered for interior applications. In bathrooms, its suitability depends on the exact product and the applications approved by its manufacturer. Check the technical specifications before using semi-vitreous tile on shower walls, shower floors, or other surfaces exposed to regular direct water contact.
Water expands when it freezes. Tile with higher porosity can absorb more moisture, increasing the risk of cracking or surface damage during freeze-thaw cycles. For exterior installations in freezing climates, use tile specifically approved and tested for the expected conditions.
ANSI A137.1 is developed and periodically revised by the ANSI Accredited Standards Committee A108, for which the Tile Council of North America serves as secretariat. ANSI approves the standard through its accredited standards-development process.
About Nova Tile and Stone
Nova Tile and Stone is a direct natural stone importer and tile retailer serving Northern Nevada and Northern California. We carry natural stone slabs, tile, countertops, hardwood and LVP flooring, pavers and exterior stone, and carpet across four showroom locations. Our commission-free team offers free design consultations to help you find the right material for your project, whether you are selecting tile for a single bathroom or sourcing stone for a full home renovation.