Membrane Installation Tips
April 15, 2008
The use of membranes in tile installations has grown dramatically during the past decade. Reasons for the growth of membrane use include increased awareness, architectural specifications, quality expectations by customers and an increase in the risk (and cost) of failures. Membranes can protect thin-set tile installation from cracking, provide waterproofing and/or reduce floor-to-floor noise. Some products provide all three functions.
There are two types of membranes: sheet and liquid (or trowel applied), and there are varieties of both. Liquid applied membranes can be one or more components. In essence, a membrane is created when the installer applies the components. Trowel applied membranes can offer advantages in areas with odd shapes and sizes.
Sheet membranes are generally made from an elastomer with bondable surfaces. This construction allows the sheet to be bonded to a substrate and tile to be bonded to the membrane. Elastomers used by sheet manufacturers vary in terms of durability, resistance to temperature and chemicals, etc. Ensure that the sheet you select has the characteristics your project requires.
Sheet membranes have some inherent benefits. They arrive at the jobsite as a finished product with uniform thickness, strength and quality. These features provide for fewer variables due to workmanship.
Regardless of the type of membrane you select, it is critical that it be installed as the manufacturer intended. Read the instructions, view installation videos and contact the manufacturer if you have questions.
Crack Isolation: Crack isolation is the terminology used by the Tile Council of North America (TCNA) to describe products that protect thin-set tile from cracking. Some manufacturers use other names like anti fracture and crack suppression to describe the function. The TCNA Handbook lists partial coverage or full coverage details for crack isolation.
Experts agree that most concrete floors will crack. Even minor cracks can telegraph and cause tile to crack. Wood subfloors are also problematic. They must meet deflection standards for ceramic or stone tile. Local code requirements are used for ceramic tile. The Marble Institute of America uses L/720 (where L = length of the longest span in inches) as the deflection standard for stone tile.
ANSI A 118.12 is the standard for crack isolation. The standard includes a measurement of performance called “System Crack Resistance.” There are two levels: Standard and High performance. In order to achieve a Standard Rating, the membrane must bridge movement of at least 1/16”. High performance requires bridging 1/8”.
The Robinson Floor Test (ASTM C 627) has also been used to characterize the performance of crack isolation membranes. The test actually determines the service rating of a tile system (which can include membranes). There are five categories from Residential to Heavy Duty. Crack isolation membranes should not reduce that service level. Ask for data from both standards to determine if your crack isolation membrane can provide the requisite performance for your project.
Waterproofing: Leaks can have catastrophic consequences, and waterproofing membranes must be watertight and last as long as the tile installation. There are thin-bed and mortar bed waterproofing membranes. ANSI A 118.10 is the standard for thin-bed waterproofing membranes. ASTM standards are used for mortar bed membranes.
Some membranes will hold water but not vapor. With the increase in concern about mold, you should protect against moisture reaching shower cavities. If you are waterproofing shower walls or steam rooms, make certain your membrane is also a vapor barrier. A moisture vapor transmission rate (MVTR) < 1.0 perm is generally considered suitable.
Generally, sheet membranes do not require curing and can be flood tested shortly after installation. Liquid applied membranes must cure which can require several days. Some sheet membranes can bridge movement joints (even expansion joints). Liquid membranes may depend on a sealant to seam membranes on either side of the joint. Product features should help determine which product should be used. However, failures are generally the result of installation error rather than the product.
Inspections and approvals: Shower waterproofing may require approval by a plumbing inspector. Municipalities generally use either the Uniform Plumbing Code (UPC) or the International Plumbing Code (IPC) as a guide.
The UPC’s approval process requires that products be tested to ensure performance. Inspectors under the UPC will generally accept a listing as proof that the product is suitable for waterproofing.
The IPC allows for the use of traditional shower pan methods like CPE and PVC sheet membranes, lead, copper and hot mopping, but thin-bed methods are not cited in the code. Thin-bed waterproofing is an alternative method in the Engineering Services (ES) section of the ICC.
Some states have their own approval processes. If in doubt, check with local plumbing officials to determine if the product you intend to use is approved. If it is not, you may be able to obtain a “variance” from the code.
Sound Control: There are two types of sound that are measured in floor to floor acoustics: Impact Insulation Class (IIC) which is footfall noise and Sound Transmission Class (STC) which is airborne noise. Tests results characterize performance with single numbers for each type of noise. Higher numbers indicate superior performance and results are not logarithmic (so small differences can be meaningful).
Impact noise is problematic for hard surfaces and an acoustical underlayment is generally required to reduce impact noise. Airborne sound is generally controlled by the floor/ceiling assembly and most underlayments offer little improvement in STC.
IIC values are dependent on the entire floor/assembly assembly. This makes it difficult to compare products based on IIC data alone. However, ASTM E 2179 testing can provide comparative data. The test measures the improvement from the topping (which includes the acoustical underlayment and flooring). The improvement is stated as a “delta”. Theoretically, you can add the expected delta to the IIC of a concrete substrate and predict the final IIC.
Resilient membranes can add to IIC but can also cause tile to crack. If the acoustical underlayment will be used in a thin-bed tile or stone installation, ensure that the ASTM C 627 service rating is appropriate for the application.
Many states and some municipalities have codified acoustical requirements. An IIC/STC of at least 50 is typical. Most condominiums state requirements for IIC and STC in their bylaws. Know the requirements in your area and the specific project before bidding.
Some final thoughts: The tile industry has experienced outstanding growth in the last decade. Failures can definitely affect the desirability, and future use, of tile. We all want customers to use more tile, and should do everything possible to protect against failures.
Ensure that the membranes you use (for whatever function) will be acceptable to local code authorities and building owners. If in doubt, seek variances before installing.
Membranes can help avoid costly problems, but they must be installed the way the manufacturer intended. Read the instructions, follow industry standards and TCNA recommendations, and you should have a good installation.