Everything You Need to Know about Mortar and Grout

Both mortar and grout are essential materials for tile installation, but they serve different purposes. Many people tend to get them confused, or even think that they’re the same thing. The two are used for different purposes and have different compositions. Mortar is used to adhere tiles to a surface, while grout is designed to fill the spaces between tiles once they’ve been installed.

Let’s start with Mortar.

Mortar is necessary for the tile to firmly stick to its substrate. There are two most common types of mortar – Mastic and Thin Set, which are often used for ceramic, porcelain, and glass tile installations. Both materials can be confusing because of several overlapping applications. So which should you use and where should you use them?


  1. Thin Set

Thin set is a type of modified mortar made specifically for tile. It is inorganic and inexpensive. Thin set can be purchased either in wet, pre-mixed or dry, powdery form. Additionally, thin set comes in either unmodified or modified versions. Unmodified thin set is composed of Portland cement, sand, and water retention agents. Modified thin set contains the same elements, along with liquid latex polymers to aid with strength and increase the working time.

Modified Thin set comes with some bonus benefits you won’t find with standard mortar. Additional products, like latex polymers, mix into dry thin set powder to increase the performance and bond strength. On the other side, un-modified thin set is a tile mortar that doesn’t contain any additives in the dry powder mix. 

  • Mastic

Mastic is an organic glue made from the sticky resin of the mastic tree. It’s available as a thin-liquid, thick glue, or a sticky paste.  Mastic tile adhesives are a great time-saver when laying tile, because they dry quickly, but they are not appropriate for use anywhere where moisture is present. 

Thin set vs. Mastic


Thin set


Moisture Factor

Thin set can be used in very wet areas, even areas that will be completely submerged in water.

Mastic can be used in dry areas only. It cannot be used in areas that will be submerged in water.

Best Areas

Thin set can be used for shower, kitchen backsplash, bathroom walls and other areas where moisture is not prevalent.

Walls, dry backsplashes are key areas where tile mastic tends to be used.


Thin set is inexpensive, and it fills in gaps and depressions.

Mastic is very sticky, grabs fast, and is quick setting.


Thin set is slow to set, which leads to tile sag on vertical applications.

(However, there are some fast-drying thin set on the market, you might want to check them out!)

Mastic can give off a sharp, strong odor that takes time to dissipate.

Now let’s talk about Grout!

Grout is used as the filler between tiles in almost every tile installation project. As it fills the gaps between tiles, also knowns as joints, it provides additional bonding, and prevents chips and cracks to the edges of the tiles. A variety of grouts are available commercially, but all of these can be classified as one of two basic types: sanded or unsanded. The main difference between unsanded and sanded grout is the presence or absence of sand. 


  1. Sanded Grout

Sanded grout is a standard grouting material with aggregate sand material added. The added aggregate material makes sanded grout much more durable than unsanded grout, for one simple reason — Shrinkage.

Sanded grout should be used for flooring and wall tile joints wider than 1/8 inch because it resists shrinkage and cracking. For pure durability, sanded grout always wins in the contest between sanded vs. unsanded grout.

**Sanded Grout Should Never Be Used For Joints Smaller Than 1/8 Of An Inch

Here is a chart for Sanded Grout Coverage and Recommended Spacing.

(based on 25 lb sanded)
 Ceramic Mosaic 1/8 inch 40 – 75 Sq Ft
 Glass/Stone Mosaic 1/8 inch 30 – 50 Sq Ft 
 Pebbles varies by sheet 20 – 35 Sq Ft
 3 x 6 inch 1/8 inch 105 – 115 Sq Ft
 4 inches 1/8 inch 105 – 115 Sq Ft
 8 inches 3/16 inch 95 – 105 Sq Ft
 12 inches 3/16 inch 115 – 125 Sq Ft
 18 inches 3/16 inch 140 – 150 Sq Ft
 12 x 24 inch 3/16 inch 130 – 140 Sq Ft
 24 inches 3/16 inch  190- 200 Sq Ft
  • Unsanded Grout

Unsanded grout is extremely sticky, because it has no additional sand or aggregate added to it. Unsanded grout should be used in joints that are less than 1/8-inch-wide. It has a smooth texture and clings well to vertical surfaces, which makes it useful for grouting ceramic wall tiles. 

The size of the tile joint usually dictates which type of grout to use, but sometimes the type of tile is the deciding factor. For example, unsanded grout is recommended for highly polished, easily scratched tiles such as marble because the aggregate in sanded grouts may damage these types of tiles. Unsanded grout should not be used in floor tile, because the grout can crack and break under the pressure of floor traffic.

Here is a chart for Unsanded Grout Coverage and Recommended Spacing.

(based on 25lb sanded)
3 x 61/16 inch40 – 50 Sq Ft
 4 x 16 inch 1/16 inch 60 – 70 Sq Ft
 8 x 20 inch 1/16 inch 90 – 100 Sq Ft
 10 x 13 inch 1/16 inch 80 – 90 Sq Ft
 12 x 18 inch 1/16 inch 120 – 130 Sq Ft