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Membrane Underlayment Buying Guide

With all of the different tile underlayments on the market today, it can be confusing to figure out what is best for your application. A traditional underlayment, such as cement backer board or plywood, is often used to give extra support to the tile or other material in flooring installations. Membrane underlayments, however, can provide anti-fracture resistance, waterproofing, impact and sound reduction, or offer a barrier for air or vapor.

There are several different types of underlayment membranes available including sheet membranes, cork, uncoupling mats, and liquid polymer membranes. Many membranes are designed to provide anti-fracture resistance, protecting the flooring or other surface from cracks that can occur in the substrate. Some membranes can also be used over existing cracks to provide crack isolation and suppression.

Underlayment membranes can be used in a wide range of residential and commercial applications including single family homes, apartments, schools, and office buildings.


Cork is a naturally occurring product that comes from the bark of a tree. Within each cubic inch of cork, there are a hundred million cells, each filled with dead air space to create pockets of air. This natural property of cork makes it an excellent sound barrier and extremely effective as an impact noise and sound reduction underlayment. Cork is also a crack isolation membrane that will help to keep stress cracks in the subfloor from transferring to the flooring surface. Additionally, cork also provides thermal insulation and is mildew and moisture resistant.

Cork is a very versatile and resilient underlayment that can be used under a wide range of flooring including ceramic tile, stone, hardwood, and laminate. Cork underlayments come in rolls or sheets with a standard thickness of 6mm that is designed to meet many building codes. Other thicknesses are also available, ranging from 3mm to 12mm, for installations that require a non-standard thickness.

Economical and readily available, cork is also easy to install and can be installed in glue down or floating configurations. Furthermore, cork is also considered environmentally friendly. The trees are unharmed during the harvesting of bark for the cork with the outer bark being harvested every 9 – 12 years.

Liquid Membranes

Liquid polymer membranes have a thick, liquid consistency similar to paint and come in a bucket or pail, usually in gallon sizes or larger. These membranes have anti-fracture, crack isolation, and waterproofing properties for tile and stone installations, making them most often used for showers, tub surrounds, spas and hot tubs, swimming pools, fountains, and other areas where waterproofing is needed.

When properly applied, liquid membranes can be used in both interior and exterior applications and are effective for both horizontal and vertical crack suppression. While excellent for waterproofing, liquid membranes are not necessarily complete vapor barriers. If vapor is a concern, such as for a steam room, then a suitable vapor barrier may need to be used in conjunction with the liquid membrane.

Versatile and easy to use, liquid membrane underlayments can be applied with a brush or roller to a wide range of substrates. Suitable substrates typically include concrete, masonry, cement plaster, cement backer board, and other commonly tiled over materials. The membrane, however, must cure before proceeding with the stone or tile installation. Once the membrane has cured, the appropriate thinset or mortar can be applied directly over the membrane and the stone or tile installed.

Sheet Membranes

Sheet membrane underlayments are thin and lightweight. They come in a roll and are often made of a flexible foam or rubberized asphalt sheet. Membranes that are “peel & stick” have an adhesive backing with a release paper on one side. They can be used in a variety of applications with membranes made specifically for use under tile and stone flooring, wood flooring, and other specific materials. Some membranes are only to be used for horizontal applications, such as floors, while others may be used in vertical applications like around doors and windows. Many are approved for use over radiant heated floors.

Tile & Stone Flooring
Membranes designed as an underlayment for ceramic tile or stone floors will typically provide anti-fracture resistance and crack suppression in the horizontal movement of the substrate or subfloor. This will help to protect tile and stone susceptible to cracking. These membranes are often vapor barriers that will help to prevent mold from growing under the tile and other problems that can be caused by moisture. Some will also provide impact and sound reduction or additional thermal insulation.

Wood & Laminate Flooring
Some sheet membranes are designed to be an underlayment for engineered wood plank, wood parquet, and laminate floors, providing a barrier for air and moisture. Membranes that are air and moisture barriers can protect wood flooring from common problems such as warping. Similar to membranes for use under tile and stone, sheet membranes to be used under wood can also provide sound reduction and thermal insulation.

Easy to Install
Sheet membranes are easy to install. Typically, they can be applied to a variety of substrates including plywood, concrete, cement backer board, and other common materials used for substrates. An appropriate primer should be used before installing the membrane - most manufacturers have a primer specifically for use with their product. After applying the primer, the membrane can be put in place and cut to the correct length. Once the membrane is in place, the appropriate thinset, modified thinset, or mortar can be applied, and the tile, stone, wood, or other material installed on top.

Uncoupling Membranes

In classical times, a layer of sand was used to separate the structural substrate from the tile. This layer of sand would help to protect the tile from cracks in the substrate by allowing the tile to uncouple, or separate, from the substrate. In more modern times, a reinforced mortar bed has been used to provide a buffer between the substrate and tile. While effective, reinforced mortar beds can add inches of additional height to the floor installation. Today’s uncoupling membranes are designed to provide a similar function by allowing the tile to move independently from the substrate but without the addition of extra height.

Uncoupling membranes come in roll, are lightweight, and easy to install. Composed of a thin sheet with a waffle-like grid or mesh on one side and an anchoring fleece or fabric attached on the underside, uncoupling membranes are ideal for protecting all types of floor tile. They can be installed on a wide range of flooring substrates including concrete, cement mortar, cement backerboard, and plywood. Furthermore, uncoupling membranes can often be installed over challenging substrates like green concrete.

In addition to providing excellent crack suppression, uncoupling membranes will typically provide vapor management properties. By allowing vapor to dissipate through channels beneath the membrane, moisture buildup below the substrate can be prevented. This becomes especially important with substrates that require a lengthy curing time. Waterproofing can also be achieved when the seams of the installed uncoupling membrane are joined together with an appropriate tape, as recommended by the manufacturer.

To install the uncoupling membrane, the fabric underside is attached to the flooring substrate with either a modified or unmodified thinset, depending on the substrate. "Peel & Stick" uncoupling membranes are also available on the market today. Next, a coat of mortar is applied over the grid, making sure all the depressions or cutaways are completely filled. With a final coat of thinset combed over the top, the tile can then be laid.