With some overlap in cementitious ingredients, grout and mortar do share a few properties. But largely, grout and mortar should not be used interchangeably. They are designed for different uses since they have different compressive strength levels, textures, appearances, and makeup.
What Are Grout and Mortar?
Grout is used for filling joints or seams between tiles, and mortar is used as a bonding agent underneath the tiles. For stone, brick, and other masonry materials except for tiles, mortar is used both as a bonding agent and as a filler for joints.
What Is Grout?
Grout fills and firms up the spaces between tiles. Grout helps to hold the tile in place (though most of this is done by the mortar, underneath). It prevents water from seeping between and below tiles, and it also makes tiles easier to clean because debris can't settle in the joints.
By bridging from one tile to the next, grout prevents chips and cracks from developing along the edges. When color-fast pigment is added, grout becomes a part of tile's overall look.
Grout is made of high-strength Portland cement, graded aggregates, polymers for pliability, and pigments for color and style.
Types of Grout
- Sanded Grout: Sanded grout feels slightly gritty because it contains sand for improved bonding. Use only for tile joints 1/8 inch or wider.
- Unsanded Grout: Unsanded grout doesn't feel gritty because it doesn't contain sand. It does have fine minerals, though. Use unsanded grout for tile joints less than 1/8 inch wide.
- Epoxy Grout: Epoxy grout has no mineral content. Because epoxy grout is waterproof, it does not need to be sealed. Use for thin joints 1/8 inch or less.
Uses for Grout
- Fills tile joints to prevent water and debris from settling in
- Provides some lateral structural support to tiles
- Bridges between tiles, limiting damage
- Adds a decorative touch to tile
Mix the dry grout with water or use pre-mixed containers of grout. After the tile has set, spread the grout across the surface of the tile with a rubber tile float, running the float diagonal to the tile.
What Is Mortar?
Mortar is a bonding agent for tile, brick, natural stone, manufactured veneer stone, and other masonry products.
Masonry mortar, a mixture of coarse sand, Portland cement, and lime, is used for laying brick and stone. A different kind of mortar, thinset, is a mix of cement, polymers, water retention compound, and a very fine grade of sand.
Easy to work with and smooth, thinset is formulated for bonding tiles to plywood, cement board, concrete, and other substrates. Thinset is also used for bonding cement board to wood substrate materials such as plywood (along with metal fasteners).
- Thinset Mortar: Used underneath tiles, whether on the floor or on the wall
- Type-S Mortar: For laying brick and stone; tuck-pointing
- Type N Mortar: A general-purpose mortar for exterior and above-grade walls
- Type O Mortar: Used mainly indoors for non-load-bearing applications due to its low compressive strength
- Type M Mortar: A heavy-duty mortar used for below-grade applications such as foundations and for heavy loads
- Type K Mortar: Soft mortar with very low compressive strength used for decorative applications
Uses for Mortar
- Laying brick for walkways
- Laying brick for structural applications
- Load-bearing walls
- Veneer stone on walls
- Applying a scratch coat
All mortar, except for thinset, comes only in dry form and must be mixed with water. Generally, an 80-pound bag of mortar mixed with 5 liters of water is sufficient to lay 35 bricks or 10 square feet of manufactured veneer stone.
Thinset mortar comes in both dry and premixed forms. A 50-pound bag of dry thinset mortar mixed with 6 quarts of water is enough to lay 75 to 80 square feet of tile. Premixed thinset mortar is more expensive but it offers the benefits of convenience and predictable mixture ratios.
Can You Use Grout and Mortar Interchangeably?
Grout and mortar should not be used interchangeably. Since both are formulated for specific uses, there is almost no overlap in function. Also, most tile manufacturers will recommend a mortar or grout, and because many tiles require specific types of mortar or grout for proper installation, you won't have much of a choice between the two.
When tile is pressed too hard into thinset mortar or when the mortar is overly thick, the thinset may squeeze up between the tiles, becoming an incidental type of grout. Having a few spots of thinset between tiles is acceptable. The thinset should never rise to the level of the tile, as this would prevent grout from covering it over.
Usually, it's best to scrape out as much of the excess thinset as possible before it hardens. Use an old screwdriver, extra tile spacer, or wet tiling sponge.
"Masonry Mortar Testing." National Concrete Masonry Association.