Dramatic lighting effects in combination with stone and tile are often desirable and striking when designed with forethought. As demonstrated in the photo to the left, the lighting effect called "Grazing" is a lighting technique used to call attention to something like a highly textured wall. The light fixture is mounted very near the wall or recessed into the ceiling at interior walls. Because the light source is located at such an extreme angle to the object, the light creates small shadows on each concave and convex texture on the wall, amplifying the fact that the wall is textured. Heavier textures can make a large space feel cozy.
Sometimes however, the Architect or Designer may not consider the effects of lighting on the visually flat tile and stone finishes they have specified for the walls or floors. That may lead to trouble for the unsuspecting stone and tile contractor and possibly embarrassment for the Architect or Designer. I came up against this challenge early in my career and since that time have been sensitive to lighting design and the way the angle of natural and manufactured lighting can affect the final appearance of tile and stone flooring and wall cladding installations.
As an example, the above photo is an exterior stone cladding project taken during the daytime when lighting is dispersed over the stone panels evenly. When you look at the photo on the right of that stone cladding at night when the down/up-lighting is present the shadows produced at the joint lines exaggerate the appearance of lippage when in fact the stone panels are within allowed fabrication and installation tolerances. I don't think it was the intent of the Architect or Designer to focus the viewers attention to the jointing between the stone cladding.
Similarly, this effect also occurs when cove lighting is installed directly above and against the walls on interior surfaces such as bathrooms, kitchen backsplashes, etc. You can see the result of cove lighting on a ceramic tile wall in the photo below. This tile is manufactured and installed within industry standards but the extreme angle of the lighting greatly exaggerates the appearance of lippage.
The following are several conditions that can exacerbate the effect of grazing light on walls and floors
• Floor and wall substrate not within tolerances
• Thinset or adhesive application of stone or tile
• Materials that are subject to inherent irregularities such as warpage
From a contractors perspective it is important that your project managers, supervisors and installers are aware of the lighting design on each project through proper pre-installation orientation.
The are some preventive measures that can be taken in order to avoid conditions. The most effective would be moving the light source 24" away from the wall which will serve to diffuse the lighting and alleviate the undesirable visual effect.
It is important for an Architect or Designer to also consider substrate conditions, installation methods and material types where grazed lighting is used in order to reduce the exaggerated shadows produced when the final installation is to appear smooth and flat.
Material selection: Large format tiles, handmade tiles, some glass mosaics, etc. have surface variations such as warpage that will be exacerbated by grazed lighting.
Natural lighting conditions: Not only manufactured lighting can cause this shadowing effect. Natural lighting will also cause this effect, especially with the rising and setting sun. Large floor to ceiling glass walled areas such as auto showrooms, lobbies, mall entrances, etc . will have a low angle of light wash over the floor at dawn and dusk if windows are facing east and west creating the appearance of unacceptable lippage when in fact the floor tiles are within allowed fabrication and installation tolerances.
Installation recommendations and precautions:
• Inspect the substrate in advance of installation. Require flat substrates that are constructed within ANSI standard tolerances.
• The installation of wall or floor should take place with the permanent and natural lighting in place to allow minor adjustments by the installation crews.
• Use a full bed mortar or medium bed mortar in lieu of a thinset installation to alleviate minor deviation of tolerances in the substrate. "Thin-set mortar installations over masonry walls with critical lighting produce an almost impossible condition for shadow free walls." from the DalTile Lighting Placement Bulletin (4/09)
• Be aware of manufacturing tolerances in the materials specified. Hand-made or molded and rustic tiles have large facial variations that will produce heavy shadowing. Large format tiles have a greater incidence of warpage and fabrication tolerances. Grout joint sizes should be determined based on the range of the facial dimensions of the tile supplied. The actual joint size should be at least 3 times the actual range of facial dimension of the tile supplied, e.g. for a tile having a total variation of 1/16" in facial dimension a minimum 3/16" grout joint should be used.
• Tile and Stone Contractors should send a precaution letter to the General Contractor or Architect advising of the potential problem with recommendations and/or hold a preconstruction meeting with them prior to the installation by others of the lighting if possible.
• Do a small mockup to show how the lighting affects the final appearance of the installation, or, after the first tiled wall is completed and grouted have the Architect inspect and approve it.
Please let me know if you think this post was helpful and any other information you would like to share regarding your experiences.