Mortar beds seem to be making a resurgence with the increased use of large tile. It’s
a little ironic to me that after almost 40 years of industry realignment caused
by the invention of thinset, we are back to a method that has worked for
thousands of years and is still the predominant method used in many countries.
With the popularity of large size tile and small grout joints, very few
substrates are suitable for direct application of tile without additional
remedial measures to flatten out the floors.
Thinset is an expensive and inappropriate material used for this purpose more
often than we would like to see. Thinset products are designed as bonding
materials. With a standard thinset the maximum bonding thickness should never
exceed 3/8 inch. If something is classified a medium bed mortar it is typically
good for a maximum bonding thickness of ¾ inch. The problem with applying
thinset that thick from an installer perspective is that you are going to be
using a lot of mid-price-range bonding material. This is a great money maker
for setting material manufacturers, but bad for the profits of the tile person,
as typically you don’t know in advance what the flatness conditions are going to
be. Self-leveling products, a misnomer if there ever was one, are also a
possibility. However they tend to be very finicky about prep prior to
application and cost wise, in our shop we referred to it as pouring dollars out
of a bag. Most are also adverse to moisture so damp floors and wet areas are a
further consideration. When possible, sometimes the best thing to do is also
the least expensive: just mud it!