Thin-set Mortar

• Thin-set mortar is applied with a grooved trowel.Jupiterimages/Photos.com/Getty Images
  
  Thin-set is a mortar that is typically made of Portland cement, fine sand and a water retaining agent. This mortar is particularly good at adhering tile or stone to concrete or stone foundations and substrates and it works well in interior applications in areas exposed to moisture. Thin-set can be used on both floor and wall surfaces. There are varieties of thin-set that will set up faster when it is important for the tile to adhere quickly.
  
  

Mastic

• Mastic is often sold in plastic containers and can be used to attach tiles in non-wet interior applications.Stockbyte/Stockbyte/Getty Images
  
  Mastic is a ceramic-tile adhesive that is sold already mixed into a paste-like consistency. Mastic is typically used to adhere back-splash ceramic or stone tiles to kitchen walls. This product is usually not recommended in high-moisture conditions such as shower walls. Mastic is an organic glue that is derived from the mastic tree. This means that when mastic is submerged in water, the adhesive fails. This also means that mastic can harbor mold and other moisture-related problems.
  
  

Modified Thin-set

• Bathroom floor tiles often require both modified and unmodified thin-set during installation.Jupiterimages/Photos.com/Getty Images
  
  Modified thin-set is similar to regular thin-set except the mixture is modified with a polymer or rubber additive. This modification allows the mortar to retain some flexibility so that when the wood substrate moves, the mortar will flex slightly rather than cracking or breaking. Modified thin-set should not be used under conditions where evaporation is difficult, such as when using a membrane product over wood. Use modified thin-set between the wood and membrane and unmodified thin-set between the membrane and tile.
  
  

Grout

• Grout is smeared over tile to get it into the gaps, and must be cleaned off the face of the tile within 15 minutes.Polka Dot Images/Polka Dot/Getty Images
  
  Grout is a cement-based mortar that is used to adhere and fill the gaps left between tiles and stones during the tile installation process. Sanded grout is used on all grout lines over 1/8 inch wide. Unsanded, a much weaker grout, is used on very narrow grout lines when the tile or stone is butted or placed very close. Grout fills in the gaps to create a smooth overall surface.