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Many years ago I began researching a methodology that would provide the highest level of protection against water vapor migration and condensation issues in shower/wet areas in the bathrooms we build.  The result of my search led me to Wedi Board.  This product was designed and has been produced in Germany for several decades.  It is available in the United States as well.  It is used commonly in commercial steam rooms – conditions that would see much more possible water issues than a typical shower.  Over the last many years it has been growing in popularity as the best protection in residential bathrooms again water and condensation issues.

Since 2005, every tiled shower pan and wall system we have built has been done using Wedi Products.  I feel that building a Bathroom Shower that is going to get tiled should be done in a manner that is built to last forever against water issues and WedI provides the best possible solution.

- Scott Hall


What is the wedi building panel?

The Wedi Building Panel is a waterproof tile underlayment for walls and floors, manufactured by wedi GmbH in Emsdetten, Germany. It consists of an extruded, polystyrene core and is covered in a fiberglass mesh and polymermodified cement coating. The blue foam core is closed cell, extruded polystyrene that does not allow the transfer of water and retards water vapor transmission. The glass mesh adds strength and rigidity to the building panels. The cement coating allows for adhesion as a bonding surface. The board is engineered to be used in interior applications for the installation of ceramic tile on walls, floors and countertops.


What is it made of? 

The Wedi Building Panel is made up of three components: foam, mesh, and mortar. The blue foam is extruded polystyrene (Styrofoam). It is inherently waterproof as it provides a closed cell matrix. This is due to the process under which the foam is created. The foam is extruded under enormous pressure, creating a dense mass of tiny, closed cells so tightly packed together that water cannot penetrate the insulation, nor can the insulating air escape from the cells. The single foam cells share the surrounding cell foam walls with the neighbor cells so that no room is left open in between the single cells in the matrix. The foam is then covered with a glass mesh to add strength and rigidity, which in turn is coated with a polymer-modified cement coating.


Why is the wedi Building Panel waterproof as opposed to “water resistant” backerboards? 

The wedi Building Panel is 100% waterproof because of the material it is made of, for example, the foam used to make a standard white coffee cup is highly compressed expanded Styrofoam However, compressed foam will allow for liquid to move around the units of which it is made. The foam that Wedi Building Panels consist of is extruded foam; this means that the foam is created through a process of infusing a styrene resin with a blowing agent. It is a single piece of foam with air pockets within.

The extruded polystyrene core is different than more common compressed expanded Styrofoam Little balls of foam are compressed tightly together to hinder the passage of liquid through the independent pieces of foam This is why a liquid stain can often be found beneath a Styrofoam cup sitting on a cold granite countertop after it has allowed vapor transfer created by hot coffee or tea. This results in a foam matrix that is honeycomb in nature. The extrusion process creates foam that is closed cell; it is lacks voids through which water can migrate.


For more information, please check out WEDI

 Related Pages:

Tile Over Drywall (Showers): A Common but Bad Practice

Quality Proven Bathroom Products

Revisiting water issues in showers: Another project we started today