Membranes & Expansion Joints

Membranes and Expansion Joints


Membranes can be the first line of defense against damage to tile work and substrates. Sometime they are required or recommended. Sometimes membranes should not be used.



VAPOR BARRIERS These membranes serve as barriers to moisture that pass through the tile work primarily on walls.  Commonly, 15 pound roofing felt or 4 mil. polyethylene film are used to retard the passage of moisture through the tile work into uninvolved space behind the tile. The vapor is allowed to pass equalizing the moisture on both sides of the wall. If a totally waterproof membrane were used on a wall, for instance, moisture vapor could collect and run down either side of the wall damaging uninvolved living spaces.
Picture water collecting in an inner wall and soaking the framing, drywall or plaster, electrical fixtures, and sub floor. I think you get the picture.


When would vapor barriers not be recommended?
When using water resistant gypsum board as solid backing, do not install a vapor barrier against the studs. Tests have shown that water vapor collects in between the board and vapor barrier. Once it turns to water as it cools, the gypsum board is compromised.


The easiest way to describe a cleavage membrane is to say that this membrane isolates the tile, bonding coat, and setting bed from the supporting element. Cleavage membranes are commonly asphalt impregnated papers, roofing felt, and polyethylene sheeting.


Cleavage membranes may also be called”slip sheets.”


Can a cleavage membrane also function as a vapor barrier? Absolutely it can. Commonly, cleavage membranes are 15 pound roofing felt or 4 mil. polyethylene film.


ISOLATION MEMBRANES These membranes are sometimes referred to as “slip sheets” in that they are designed to isolate the tilework from the substrate below. There are few isolation membranes manufactured for this purpose and they have to be installed by carefully following the Manufacturers recommendations.


There are other “slip sheets” used today that were not manufactured for that purpose. Many of them work, at least, temporarily. Think of the tilework above the substrate as a sandwich. Each layer is bonded to the next. If one of those layers loses it bond, the entire installation can fail.


As an added precaution, if a membrane is installed as a “slip sheet” and the product was not manufactured for that purpose, the Manufacturer may not warrant the installation if a failure occurs.
These membranes have a specific purpose. They have recommended characteristics that need to be present for them to perform correctly. Waterproof membranes need to be exactly that-100% waterproof.


There are several types of waterproof membranes available today. Some are made of common construction materials and are made at the jobsite. Others are manufactured in sheet or rolled forms. Still others are liquid applied.


Lets look at the types of waterproof membranes in use today.


This first type is also the oldest. Layers of 15 pound roofing felt are placed in the desired area and each layer is coated with still molten tar. This process is called hot mopping, referring to the hot tar being mopped onto the paper. A certain number of successive layers are required for certain applications. This process is used for roofing certainly. However, in our industry we see this process used for exterior decks and shower pans. This type of membrane is made at the jobsite.


These membranes are manufactured and are available in small and large sheets, rolls, and liquid. Various manufacturers make these membranes in various thickness. Some are designed for waterproofing only. Still others have chemical resistance as their primary goal. There are liquid applied membranes that are designed to act as a waterproofing and as a bond coat for tile.


The suppression systems available today fit into this category. They are found in sheet form and are bonded directly above the to isolate the tile above from the below.


Tile Doctor Tip: It is imperative to closely follow the Manufacturers recommendations for their use.


Regardless of the type of membrane, ANSI 118.10 has guidelines for waterproof membrane performance. ASTM testing methods sets the guidelines. For example, the testing method for waterproof nature of the membrane is ASTM D 751. This simply indicates that there is no water penetration when tested. The membrane must not break when subjected to a load of greater than 170 psi as tested under ASTM C 482. The membranes should also be mold and fungus resistant.


This testing is important as these membranes are used for a variety of uses. Their performance is crucial when their use is necessary. For more on membranes, refer to the specific area of The Tile Doctor for your project.