In the building industry, a membrane usually refers to an underlayment
that is a thin product providing separation or transition from one concrete
material or application to another. In the ceramic floor tile industry,
a membrane refers to an underlayment that is applied between the substrate
and the flooring tile or tile assembly. Membranes are used for a variety
of reasons so there are many types that are designed for specific functions.
The purpose of this report is to identify and define crack isolation
membranes and their intended use. Crack protection is limited to minor
horizontal planar movement of the substrate (shrinkage cracks) and will
not provide protection against vertical movement (structural cracks).
See industry standards ANSI A118.12* for material and ANSI A108.17* for
installation (*pending approval at the time of this report).
I – MEMBRANE CATEGORIES
LOAD BEARING, BONDED, CRACK ISOLATION MEMBRANES: (ANSI A118.12*)
Membrane strips are bonded to the substrate and are specifically
designed to cover existing shrinkage cracks in the substrate per
TCA F125. The membrane strips must cover three times the width
of the floor tile used, with a minimum width of 6 inches. Check
with the membrane manufacturer for the maximum crack width that
is covered by their membrane warranty and any limitations. These
types of membranes can also be used as “anti-fracture” membranes
when they are applied to the entire surface of the substrate.
LOAD BEARING, BONDED, ANTI-FRACTURE MEMBRANES: (ANSI A118.12*)
This membrane is bonded to the substrate. It is only considered “anti-fracture” if
it completely covers the substrate per TCA F125A. This is a full
coverage membrane designed to manage both existing shrinkage cracks
and future ones; it also provides some protection against shrinkage,
thermal and moisture expansion/contraction of the substrate.
CLEAVAGE MEMBRANES: (ANSI A-2.1.8)
This is a full coverage membrane that is not bonded to the substrate
with the purpose of
separating the entire tile assembly from the substrate. This isolates
both the wire-reinforced mortar bed and the tile installation from
any instability in the wood or concrete substrate.
LOAD BEARING, BONDED, UNCOUPLING MEMBRANES:
This is a full coverage bonded membrane that differs from other “direct
bond ‘anti-fracture’ membranes” because it is a
thicker material with air cavities pressed into its surface. The
patterns are designed to “keylock” the thin-set into
its upper surface, while the open air cavities underneath allow for
some lateral movement without losing a bond per TCA F147/F148.
LOAD BEARING, BONDED, WATERPROOF MEMBRANES: (ANSI A118.10)
This type of membrane is not covered in this Field Report. If you
require a waterproof membrane, please refer to CTIOA Field Report
82-1-3 (R-2002 ‘Waterproof Membranes & Underlayments’ available
on the Web at www.ctioa.org.
II – TYPES OF INDIVIDUAL MEMBRANES
LOAD BEARING, BONDED, CRACK ISOLATION & ANTI-FRACTURE
MEMBRANES:
- Sheet membranes bonded to the substrate with some available in
a “peel & stick” type of material.
- Rolled liquid or trowel applied membranes that are bonded to the
substrate with or without fabric. Some require fabric embedded over
the entire substrate while others only require it over backer board
joints and at all changes in plane. When cured, tiles are typically
thin-set directly onto the membrane. Always refer to manufacturers’ instructions
for performance levels and limitations, and be sure to follow the
written instructions accurately to avoid problems.
- Some trowel applied membranes can be used as a bonding agent for
tiles as long as the tiles are applied before the membrane sets.
- Cork underlayment on Concrete, TCA F135-03: “½-inch
thick (+/- .010-inch) cork underlayment sheets. Consisting of a mix
of pure cork granules combined with polyurethane binder, having a
density of between 11.8 and 13.6 lbs. per cubit foot.”
NOTE: TCA states under F135-03 to use a Type 1 organic adhesive to
bond cork underlayment to sub floor. CTIOA warns regarding concrete
slabs on grade: “Organic adhesive should never be used to bond
sheet type membranes onto a concrete slab on grade because of the
potential for moisture problems.”
CLEAVAGE MEMBRANES:
- Cleavage membranes are designed to separate the tile assembly’s
mortar bed from the surface of the substrate.
- The mortar bed is required to be reinforced and to be of a uniform
thickness – 1-¼" minimum to 2" maximum (ANSI,
TCA). Mortar beds (reinforced) in excess of 2-inches shall be detailed
by the architect. For reference details, refer to TCA F111-03, F114-03
over concrete floors, TCA F141-03 over wood floors.
- Membrane sheets approved as cleavage membranes should never be
used, nor are they ever recommended by their manufacturers to be
used, as a “load bearing, bonded, crack isolation or anti-fracture
membrane.”
LOAD BEARING, BONDED, UNCOUPLING MEMBRANES:
- Uncoupling membranes are used on problematic substrates to prevent
any existing or potential cracks and stresses from transferring to
the finished tile assembly. When there are height limitations, the
uncoupling membrane is an alternative to using a reinforced mortar
bed over a cleavage membrane. For quick reference details see TCA
F147 and F148.
- This membrane is a full coverage “load bearing, bonded,
anti-fracture” membrane.
- The material that forms this membrane is considerably thicker
than any of the other membranes.
- This single sheet membrane is available with a number of different
patterns pressed into it. The intended use of the membrane will determine
which pattern should be used.
The patterns are designed to “keylock” the thin-set into
the membrane’s top surface while providing mesh covered air
cavities underneath to allow for some lateral movement without losing
bond. *
* NOTE: There are other pressed patterns available in ‘uncoupling’ membranes
for different uses. For this report, however, we are only reviewing “load
bearing, bonded anti-fracture” membranes.
MOISTURE VAPOR EMISSION & MEMBRANES:
Not all membranes are suitable as vapor barriers and should be used
only as per the manufacturer’s instructions. Floor membranes
are usually classified as either a moisture barrier or as a vapor/moisture
barrier. A MOISTURE BARRIER is designed to substantially reduce or
eliminate moisture in a liquid state from passing through it; but
it is breathable and does allow moisture in a vapor state to pass
through it, to some degree. A VAPOR/ MOISTURE BARRIER does not allow
moisture in a liquid or vapor state to pass through it; thus it is
not breathable. In cases where the substrate’s moisture vapor
transmission exceeds 3 lbs per 1,000 square feet in 24 hours, consult
with the membrane manufacturer for suitability of use. The Marble
Institute of America (MIA) recommends that all on-grade applications
have a moisture barrier to protect the natural stone against potential
moisture problems. Carefully consider all options, as improper use
of a vapor/moisture barrier membrane may entrap moisture condensation.
SLIP-SHEETS:
“Slip-sheet” is an incorrect term used to describe all of the above
membranes. In the past, the term “slip-sheet” was synonymous with
cleavage membranes. Today “slip-sheet” is a term used by the Ceramic
Tile Institute of America (CTIOA) to describe materials such as 15 lb. felt building
paper, scribing felt, or Kraft paper. These products are misused as load bearing,
bonded, membranes in order for contractors to reduce material costs. Slip-sheets
are not recognized by the CTIOA or their manufacturers as an acceptable alternative
or replacement for industry approved “load bearing, bonded, crack isolation
or anti-fracture” membranes. This is due to their initial low tensile (shear
bond) values and their rapid deterioration when exposed to moisture condensation
with high alkalinity that are common with concrete slab on-grade tile applications.
CONCLUSION:
There have been many tragic failures when the wrong membranes have
been used or where the membranes and/or the bonding mortars are not
compatible, resulting in loss of bond. The reason for most failures
where membranes are involved is that an inappropriate or unapproved
membrane was used, or it was improperly installed for the kind of
application for which it was being used. There are two requirements
to consider when selecting the correct membrane to use:
- Membranes must meet all current ANSI standards.
- All manufacturers’ instructions must be followed and limitations
considered when membranes are installed.
ADDITIONAL SOURCES OF INFORMATION
For additional information on membranes and related subjects, see
the following CTIOA publications.
- Field Report 82-1-3 ®-2002 – ‘Waterproof Membranes
and Underlayments’ (ANSI A118.10)
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