A.Michael Byrne, a tilesetter
and industry consultant from Los Olivos, Calif., responds:
First, there are several mortar bed installation methods that
require no reinforcing. These are typically for floors where
you're putting a bonded mortar bed over an intact
slab-on-grade. These methods, which are based on ANSI A108
specification standards, are described and illustrated in the
Handbook for Ceramic Tile Installation, available from
the Tile Council of America (864/646-8453,
For thick mortar bed installations over
wood floors (left), ANSI specs call for wire fabric reinforcing
and a cleavage membrane between the subfloor and the mortar.
For thin mortar beds (right), use expanded metal lath nailed or
stapled to the subfloor.
I'll assume you're talking about laying a mortar-bed tile
floor over wood framing. The tile industry recognizes two
methods for reinforcing mortar setting beds for floor tiles
over wood-framed floors (F141 and F145 in the TCA
Handbook). The difference in the two methods has to do
with the thickness of the mortar.
For thick bed installations — from 1 1/4-inch minimum to
2-inch maximum thickness — the ANSI A108 specification,
A-2.1.7, calls for one of the following welded wire
- 2x2-inch x 16/16 wire
- 3x3-inch x 13/13 wire
- 1 1/2x2-inch x 16/13 wire
- 2x4-inch x 16/16 wire
For this type installation, the thickness of the mortar
requires that the reinforcing fabric be positioned somewhere in
the middle of the mortar bed. When I set tile using this
method, I'll dump about half the mortar on the floor, lay the
wire mesh on top of that, then spread the rest of the mortar.
This works fairly well with mud-bed mortar because it's fairly
dry and will support the wire. It isn't necessary to use any
other supports for the wire.
The thin mortar bed method (3/4-inch-minimum thickness) calls
for flat, expanded metal mesh weighing not less than 2.5 pounds
per square yard. Painted lath is allowed, but galvanized lath
is preferred. The TCA F-145 detail shows the lath fastened
snugly to the subfloor, with a cleavage membrane installed
between the two.
In either method, a cleavage membrane, which can be 15-pound
asphalt-saturated roofing felt or 4-mil poly, separates the mud
from the wood floor and prevents the wood subflooring from
drawing moisture out of the mix during the curing phase.
I prefer mortar beds for tile floor installation because they
provide a smooth, flat surface for tilesetting, but they
require specific detailing beyond the type of mesh to use. If
you plan to use mortar setting beds, get a copy of the TCA
Handbook for a review of all the details.