Uneven Mixing

• The mixing process is one of the most important aspects of grouting. There are a variety of pigments, polymers and dry materials within a bag of grout, and in order for all of those components to blend together properly they must be mixed according to the manufacturer's instructions. Failure to follow these mixing instructions can lead to the grout colors not blending or the polymers not mixing together properly, which can lead to grout lines that are uneven in size due to chunks of unmixed materials.
  
  

Excess Water

• Too much water in the mixing process leads to soupy grout. If the soupy grout is then used to grout the tiles, it will be too thin and will not fill the joints properly, leading to valleys where the grout is not flush with the finished surface, as well as irregular widths due to inadequate cement-to-water ratios.
  
  

Improper Cleaning Methods

• Failing to follow the proper cleaning methods during the grouting process will lead to irregular-sized grout joints. Wiping with the joint, for example, will cause the sponge to dig grout out of the joint instead of allowing it to stay full and flush with the finished surface of the tile. Using an overly wet sponge, or applying too much pressure during the washing phase, can cause the same thing to happen.
  
  

Over-cleaning

• One of the mistakes people make when cleaning the tile during the grouting process is over-cleaning. The desire is to remove as much of the grout film as possible in order to avoid grout haze from developing during the drying phase. Too much pressure on the sponge is one problem, but the other is when people use too much water in the sponge during the washing phase. Excess water can lead to grout failure, as the excess water will cause the grout to turn into powder once it dries, as the cement-to-water ratio is ruined. This leads to gaps and irregular-sized grout joints.