Flooring Installation

• Mortar is the glue that holds many flooring materials tightly to the subfloor below them. This adhesive is strong and stiff, but also flexes slightly to prevent damage to the flooring, according to Fine Homebuilding. Mortar is comprised of a mixture of cement and lime, mixed with water to make it a malleable and spreadable paste. Grout doesn't work as an adhesive because it isn't very strong, but it is used in conjunction with mortar applied underneath the flooring materials.
  
  

Aesthetics

• While mortar holds your ceramic or porcelain tiles securely to the subfloor, grout plays primarily an aesthetic role. Grout is made from the same ingredients as mortar, but in different proportions. Tiles must be installed with small gaps between them so they don't rub together and break as you step on them. Filling these gaps with grout create a better looking floor and keeps dirt out, according to Grout Perfect. Grout also offers some protection to stop water from reaching the sub floor.
  
  

Bricks and Blocks

• Mortar also is used between bricks and concrete blocks when building walls. This is known as masonry mortar and is composed of slightly different materials. Most modern masonry mortars are made from a combination of masonry cement and fine sand, according to Sakrete. This type of mortar is not as strong as concrete or pure cement because it is designed to break under extreme force instead of letting the brick or concrete blocks break. You have a better chance of repairing the wall without replacing it when the materials are fine.
  
  

Differences

• Mortar and grout are mixed from the same basic ingredients of cement and water, with the option for aggregates. Grout contains more water than mortar according to the Masonry Advisory Council. This allows it to flow into the small gaps between flooring easily. The lower ratio of cement to water also makes grout weaker and is why it isn't used as an adhesive, like mortar. Some forms of grout and mortar contain sand to create a thicker mixture for filling larger gaps.