The National Tile Contractors Association (NTCA) along with other industry professionals have proven that specific methods of applying thinset mortar will have very distinctive results. Directional troweling as seen in the photo to the left will result in a greater than 95% contact bond when done correctly.
The swirling troweling method as seen in the photo to the right typically results in air pockets that creates voids in mortar bonding to tiles.
In some tile applications the back butter troweling method assists in obtaining greater mortar coverage. When done correctly a 95% or greater coverage can be obtained.