FAQ - Building Panels and Fundo Shower System

Frequently asked questions on wedi building panels & wedi Fu

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, as well as in the USA , in wedi’s factory in Batavia, Illinois. It consists of an extruded, polystyrene core and is covered in a fiberglass mesh and modified cement resin coating. The blue foam core is closed cell, extruded polystyrene that does not allow the transfer of water and retards water vapor transmission but is not a vapor barrier. The alkali resistant glass mesh adds strength and rigidity to the building panels. The cement coating allows for adhesion as a bonding surface to any standard or modified tile adhesive on cement or epoxy basis. The panel is engineered to be used in interior applications for the installation of ceramic tile, stone or glass tile and various other finishes from stucco to laminates: on walls, floors, countertops and many more applications where traditional backer boards are used. The wedi Building Panel is available in 2' x 4', 3'x5' , 2'x8', 3’x8’, 4’x8’ sheets in various thicknesses 1/8", 1/4", 1/2", 5/8", 3/4”, 1", 1 1/4”, 1 1/2" and 2"

What is the building panel 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. It offers no capillary activity. The foam is then covered with a glass mesh to add strength and rigidity, which in turn is coated with a modified cement resin coating.

Who produces it?

It is manufactured in by wedi GmbH in Emsdetten, Germany, as well as in the USA , in wedi’s factory in Batavia, Illinois.

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

The wedi Building Panel is 100% waterproof because of the material it is made of. 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. This results in a foam matrix that is honeycomb in nature. The extrusion process creates foam that is closed cell; it lacks voids through which water could migrate. It has zero capillarity and cannot wick water.
For example, the foam used to make a standard white coffee cup is highly compressed expanded Styrofoam. However, this compressed foam will allow for liquid to move around the units of which it is made.
With this EPS foam, 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. Commonly, EPS foam may absorb water up to 15% of its volume. EPS density will make this foam’s rigidity higher, but it will not make it waterproof. Other foams, including Polyurethanes, are rarely used for waterproofing either. Their cell structure is often inconsistent offering varying degrees of water absorption.

What sizes are available?

The wedi Building Panel is available in 2'x4', 3'x5', 2'x8', 3’x8’, 4’x8’ sheets in various thicknesses 1/8", 1/4", 1/2", 5/8", 3/4”, 1", 1 1/4”, 1 1/2" and 2".

How much do the wedi building panels weigh?

The wedi Building Panels vary in weight depending upon the thickness of the board. In the 3 x 5 ft. size 1/4" is 8.07 lb, 1/2" is 8.67 lb, 5/8" is 8.97 lb and the 1" is 11.4 lb.

Does the wedi building panel have an R-Value?

Yes. The R-value varies depending upon building panel thickness at a rate of 4.3 per one (1) inch.

Does the wedi building panel have a fire rating?

The wedi Building Panel will not provide a fire barrier. It will not add anything to a fire or fuel a fire, as the cells of the foam will collapse due to extreme temperatures above 175°F. It passed the Steiner Tunnel Test/ ASTM E84 with a flame spread of <20. Where a one-hour firewall is required, the wedi building panel should be applied over a surface that can provide such a rating (such as certain drywall systems).

Can wedi building panel be used on floors?

Minimum 1/8” thick wedi Building Panel functions as an excellent substrate for most flooring applications. wedi Building Panel  ¼” over standard EGP plywood structure 16” o.c.,  and installed with 3x4” tile using standard cement based setting materials, has been rated for heavy-duty commercial use by the Tile Council of North America (TCNA) using the industry standard known as the Robinson Floor Test (ASTM C627). It can be applied over a wooden or concrete subfloor. When applied over plywood, the recommended joist spacing is 16" on center, 23/32" or greater plywood with no deflection in the subfloor greater than L/360 as outlined by the TCNA, following local building codes or the IRC.
L / 360 equates to the length of the span between floor joists then divided by 360. If applied over a cement subfloor the slab should be fully cured and free of debris. A full cure is not necessarily reached after 28 days as is often, and falsely, claimed. Only CM / core probe measuring may reliably determine the status of a concrete slabs curing process. The board will function as a crack bridging membrane because cracks in the cement subfloor will not likely transfer through the foam as easily as through other inelastic tile backer boards.

On the floor should I leave room for expansion joints between wedi Building Panels?

No, the wedi Building Panel is inert and will not shrink or expand over time. All wedi Building Panels should be butted together and laid staggered. An expansion joint around the perimeter of the floor should be considered, leaving a gap of 1/8" to the surrounding walls to better resist structural movement. Consider the use of expansion joints in your tile assembly over wedi products according to Recommendations found in the Tile Council of North America’s Handbook for Ceramic Tile Installation. Our building panels should not be installed over expansion joints in concrete slab construction.

Should I stagger my joints?

Yes, the wedi Building Panels should be staggered to minimize the length of the surfacing of potential breaks/ cracks in the substrate.

Can the wedi Building Panel be installed on walls?

The wedi Building Panel can be applied directly to wood or metal studs, over primed gypsum board (green board or drywall), masonry walls and existing ceramic tile. The recommended thickness for a stud wall application is 1/2", 5/8", 3/4”, 1”, 1 1/4”, 1 1/2” or 2”. Thinner panels may be installed over solid surface substrates. The particular thickness is dependent solely upon the desired effect that the contractor wants to achieve. If a contractor is applying wedi Building Panels over a gypsum product, the 1/2" board will most likely be used as this will allow for the trim pieces of ceramic tile to cap where the wedi Building Panels end.

Can I install the wedi Building Panel directly to the studs?

Yes, minimum 1/2" thick wedi Building Panels can be fastened directly to wood or metal studs with only a few fasteners per sheet {one (1) wedi Fastener per one (1) ft. of stud}. When the board is applied directly to studs the 5/8" material can be used if the ceramic tile to be applied will have a flush or surface finish with tiled 5/8” drywall in adjacent, dry areas. The 1" board can be applied directly to studs if a "floated" look is desired or over 19” o.c. framework. The framework itself must be designed as a loadbearing, suitable substrate. All vertical wedi Building Panel ends at framework corners must be fully supported by framing.

How do I install wedi building panel over framing which is not plumb, or not straight or not squared or show any combination of these issues?

As with any other backer board and tile underlayment, you will need to create a surface that is loadbearing, true and flat, as well as plumb and squared from floor to ceiling.

Unfortunately , many 2x4 wood framing studs are not in a perfect  condition or framed perfectly fine.

It is important to deal with the deficiencies of framing prior to installing wedi panel or any other tile backer board. If you choose not to, these deficiencies will either show later, when the corrections are done in the tile surface layer or the backer boards cannot be installed tightly fitted below the tile.

Here are safe and good ways to ensure proper framing before installation of wedi building panel:

  1. Use wood furring strips nailed to studs, either along entire studs or parts of studs
  2. Sister studs, replace studs, add cross blocking

Here are methods NOT to use, without limitation:

  1. Wet or Dry shimming with sealants, caulks, or other types of adhesives (cement thinset mortars or other types including general construction adhesives)

wedi Building panel must be mechanically affixed to framing which provides the properties needed to safely support the building panels. Only wedi fastener systems are used.

Can I install the wedi Building Panel over green board/drywall?

Because the wedi Building Panel is 100% waterproof, it is not necessary to use green board/drywall behind the installation. However, it is common for this material to be applied in wet areas and it has no detrimental effects on the installation if waterproofed with the wedi Building Panel. Before installing wedi Building Panel over any gypsum containing product, a primer must be applied prior to application of thinset mortar which is used to attach the wedi to such drywall assembly. Fasteners may be set in some areas to temporarily attach the two boards and compress the thinset adhesive. Do not forget to seal such fastener points with wedi joint sealant.

Can I use the wedi Building Panel in an exterior application?

The wedi Building Panel is not recommended for use in a horizontal exterior application. On a vertical surface, the wedi Building Panel can be used in certain instances. Please contact wedi Technical Service when planning this type of installation.

Can I install wedi Building Panel in a steam shower or steam room?

Yes, wedi is the preferred choice of backer board worldwide for more than 30 years when it comes to steam rooms. wedi panels are not only waterproof but also function as a vapor retarder. However, wedi does not support the current industry standards as per the TCNAS, nor does wedi support the suitability of the Test method applied (ASTM E96 E). Even products that meet the industry standard for continuously used steam rooms of .5 PERM are not proven by any substantial research to be effective retarders in all steam room – and shower installation situations. In addition, wedi realizes that only an entire interior vapor retarding concept and installation will be effective. In other words, all protrusions, seams, fastener points must be designed and installed to retard water vapor successfully. This is why wedi favors over and in addition to its closed cell foam products (a) extra safe strength vapor retarders and (b) full surface vapor retarders installed on the entire interior wedi surface prior to tiling.   

wedi therefore recommends the application of the wedi epoxy based vapor barrier (= effective retarder) or wedi Subliner Dry (= effective retarder)  over its closed cell and cement resin coated foam product in steam room/shower applications. Using thicker wedi panels than the common ½” wall/ceiling backer boards over framing will offer some added value: increase of insulation value which will dramatically add to the energy efficiency of steam generators which are operated by temperature feelers. As well as that intersections and transitions to sloped ceiling panels can be installed in a safer (interlocking) method.

Adding wedi’s vapor barriers will ensure decades of safe functionality of a steam room application- no matter whether commercial or residential steam room/shower. wedi diligently works in technical committees of NTCA and TCNA to change the industry standards to increase the required strength of a vapor retarder and/or barrier in steam room installations. wedi building panels also provide a thermal insulation value , minimizing the water vapor pressure differential to the outside area behind the wall and ceiling substrate and adds to energy efficiency through insulating the warmth in steam rooms. Please see wedi’s full guidelines for residential and commercial steam rooms on this website in the technical data sheet “wedi Building Panel”.

Can I install wedi Building Panel in a Dry Heat Sauna?

No, wedi Building Panels should not be installed in areas subject to temperatures above 175*F. The foam could deform in such installations and applied tile could heat up to a point, where users could get hurt.

Can I install wedi Building Panel in and around Fireplace applications?

This would depend on how close the wedi building panel will be located to the heat. wedi Building Panels should not be installed in areas subject to temperatures above 175*F.

Can I install wedi Building Panel in a swimming pool?

No. With the assumption of perfectly installed seams in a wedi Building Panel assembly, wedi could be used in pools. wedi Building panels are 100% waterproof. Due to high water pressure in large pools and the inevitable high number of seams and other protrusions ( lights/fixtures), we do not recommend the use of wedi products in swimming pools or other pools. wedi offers premade customized pools and pool modules- made in the wedi factory in a controlled environment and using computer aided design and manufacturing robot technology for precision work results needed in such challenging applications.

Can I install wedi building Panels in conventional concrete or pan liner shower floor installations?

Yes, unlike with cement based backer boards, you can actually install the wedi building panels all the way down to the pan liner, before you float a concrete base against them. The result is a square, plumb installation ready for tile. wedi building panels, unlike cement backer boards, do not wick water.

Can I use the wedi Building Panel in an exterior application?

The wedi Building Panel is not recommended for use in a horizontal exterior application. Too much movement potential, especially over wooden deck or patio construction, and the many application specific, complicated details to be considered (flashings etc.) are frequently challenging the tile installing trades. wedi therefore does not warrant or support tiled decks or patios in which wedi is a part of the assembly. Please contact wedi Technical Service when planning this type of installation on a vertical surface, the wedi Building Panel can be used in certain instances such as facades. Please consult wedi for proper installation in different climate zones of North America. On facades, please integrate wedi building panel into the building envelope considering that wedi Building Panel functions as an insulator and also vapor retarder. Its proper positioning in an exterior wall assembly is therefore depending on the climate zone in which the installation is done.

How is the wedi Building Panel cut?

The wedi Building Panel is cut with a utility knife, scoring is unnecessary as the blade will be able to penetrate through the board. Mechanical saws and handsaws can also be used.

The wedi Building Panel can be dented when pressure is applied, will this cause problems after the ceramic tile is adhered over these dents?

No, once the cells in the foam are broken they will not re-inflate. When thinset mortar is spread over these indentations the voids are filled and will set as such. As long as the wedi Building Panel is not punctured all the way through the foam, the waterproof qualities of the board will remain. In situations where this is unavoidable (such as at the attachment points where screws are used) wedi Joint Sealant must be applied.

Is the wedi Building Panel strong enough for my ceramic tile installation?

The wedi Building Panel has been rated for heavy-duty commercial use by the Tile Council of North America (TCNA). This means that wedi Building Panels can serve as an underlayment on floors in a residential application such as kitchen or living room floors, in bathrooms or stairways, as well as spaces such as office buildings, breweries or anywhere that there is heavy duty use. When installed on walls, wedi Building Panels can support any standard ceramic tile or natural stone (up to 23 pounds / sqft). On ceilings, it can bear up to 18 pounds/sqft. The board will not fail under normal conditions, including moderate impact, such as the weight of an adult person or the blow of a wayward refrigerator.

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