A Slate Primer

The Skinny on Slate

What is slate?
Slate is a natural stone or rock. Rock is made up of minerals and other rocks that give it color. Natural slate usually refers to two different products; slate that originated as shale, and quartzite that originated as sandstone. Both products are metamorphic rocks, which means that over time, and under heat and pressure, they have changed in form from their original appearance and characteristics. Both slate and quartzite are quartz-based (siliceous) products. This means they share certain characteristics with granite (another siliceous stone), the most important being chemical and acid resistance.

How is slate produced?
When you look at the edge of a slate tile, you can see it’s comprised of multiple thin layers. These layers indicate how slate looks in its natural form. Slate is usually split from the quarry in layers. These layers form surface clefting, which is gives slate its pronounced surface texture. The slate is then cut into tiles or trim shapes, and it can be natural clefted, tumbled or honed.

What is honed slate?
The face of a slate tile is naturally clefted or uneven. However there are applications where a smooth face is desirable. Some slates and quartzites can have the face ground down to a smooth faced product. This process is known as honing. Many honed quartzites still have an appearance of depth and texture because of their mineral content.

What is gauged slate?
Grinding or machining one side gauges the slate. Gauging is done for two reasons: to create thickness within a defined range and to provide a flat back for ease of installation. Keep in mind that gauged slate will vary in thickness, but the range of thickness is less than a natural random thickness. Think of slate as a naturally rough stone. It’s cut into squares and gauged but not within the precise dimensional measurements of other stones like travertine or granite.

What colors does slate come in?
Slate factories may mix tiles from multiple quarries to develop extreme color ranges, and there are slates that are fairly consistent in color. You’ll find that most slates are within a color spectrum like golds and greens, browns and blacks, reds and rust or sandy beiges. Slate should be initially selected from an array of 6-9 samples tiles in order to see the anticipated color range. Final selection should be from as many pieces as you need to see to feel comfortable with the color range. This can be as few as 3-4 pieces, a picture of multiple pieces, or several actual pieces from each pallet that you’ll be receiving. See enough pieces in order to be assured that the slate you receive meets your expectations before your signed approval.

Can slate be installed outdoors?
Slate is a great choice for many outdoor installations. The natural textured (clefted) face of a slate tile provides excellent slip resistance. The multiple earthy colors of slate complement almost any style and color scheme. There are even a few slates that can withstand intense freeze-thaw cycles, but request written laboratory test results before installing slate in snowy conditions.

Can slate be installed in wet areas?
Because of its density and high chemical resistance, slate is ideal for use on patio and pool decks, as well as kitchen and baths. Slate isn’t usually recommended for areas with standing water such as inside pools, waterfalls or fountains. Natural stones should never be used in steam showers.

Should slate be sealed?
It’s not usually necessary to seal slate outdoors. However, as with any natural stone tile, slate installed indoors should be sealed with a high quality penetrating sealer. Sealer should be reapplied every 1-5 years depending on manufacturer’s recommendations and usage. Put a drop of water on the surface. If it beads up, your sealer is working. If it doesn’t, it’s time to reseal.

Insight
The objective is to understand the color, appearance and performance characteristics of the slate tile before it’s shipped so that the final installation would not only meet the buyers expectations, but will be more beautiful than they ever imagined.

Five Tips on Tile

Five Tips for Designing with Tile

1. Design with color

  • Color can change the mood of a room, highlight its good points and obscure its bad points
  • Counters and walls can use tiles that complement or contrast in color to those used on the floor
  • Tile can be cut into one-quarter size and alternate colors to create custom borders

2. Design with direction

  • Tile can be set with a straight joint, brick joint, or patterns such as herringbone, basket weave, etc
  • Change direction from straight set, to a 458 angle in another room to define different areas of the home
  • Use modular sizes of tile, to create patterns
  • Change sizes to delineate specific areas

3. Design with size

  • Use modular tiles in two or more sizes to create multiple piece patterns.
  • Change sizes within an installation to create unique effects or to delineate specific areas or rooms

4. Design with decorative factory pieces

  • Tile can be installed in an “area rug” configuration
  • Medallions can be tied in with the home’s architecture
  • Use listellos to border or personalize any room
  • Custom fabricate tiles using water jet technology

5. Design with relief and texture

  • Use various textures together for unique effects
  • Tile provides the ability to inset different tiles or stones
INSTALL PRINCIPLES

Installation Principles

This system consists of four integral components. The failure of any component means the failure of the entire installation.

1. Substrate

What is the condition of the substrate that you’re going to set the tile on? Is it clean and ready for tile? Is it properly cured? How will cracks be prepared? Is it level? Are there any humps, bumps or dips? How will you address expansion joints? The number one job complaint received by the Tile Council of America (TCA) revolves around inadequate preparation of the substrate and no expansion joints. Use the TCA Handbook for information regarding placement of movement joint’s.

2. Tile, trim and installation materials

Tile. “It’s all good”. Overall, tile is much better than it was 20 years ago. There are a few sub-standard products, but by and large tile is a bargain over the life of the product when compared to other flooring surfaces.

Trim. Make sure that the trim shapes perform the intended function and that they coordinate in color, shade, thickness and overall dimensions with the tile.

Installation Materials. If you skimp somewhere, don’t skimp here. As a matter of fact, many thin-set manufacturers offer lifetime warrantees on their premium polymer or latex modified setting systems (thin-set and grout). Pennies a foot for a lifetime warrantee? Sounds like a bargain insurance plan to me!

3. Installation, caulking and clean up Installation.

Sure tile is a great DIY product, however, you cannot beat the finished look of an installation when completed by a true professional. A professional tile setter will make sure that the substrate is ready to accept the tile, select the proper installation materials, layout the installation in a manner that will enhance the overall appearance and give you an installation that will last at least 40 years.

Caulking and clean up. The difference between a good installation and a poor installation is in the details. The caulk joints, the grout clean up and the overall condition of the installation is critical to produce a beautiful job.

4. Cleaning and sealing

Most slip-fall accidents don’t come from the wrong product being installed, but from inadequately maintained surfaces. As a rule, tile should be cleaned with a neutral cleaner. Vinegar, the cleaner we all used to recommend, won’t harm most tiles, but can destroy the grout – don’t use it. Change your mop water often. Hint: throw a quarter in the bottom of your mop bucket. When you can’t see it-change the water.

Sealing. Glazed ceramic tile is never to be sealed. All stones must be sealed. Many unglazed porcelain tiles must be sealed. Sealing the grout can bring the absorption of a latex modified grout down to less than 1% absorption. Sealing makes it easier for you to clean your grout, but your grout still requires cleaning (where’s that self-cleaning grout?). My personal recommendation: pick out a dirty colored grout and you’ll always be happy.

Performance-Ratings - Tile and Stone by Villagio

Performance Ratings

PEI ratings PEI rates abrasive resistance of the tile’s glaze on a scale of 0-5. This test is only for glazed tiles and does not apply to unglazed porcelain tile or other unglazed types of tile. Deep abrasion test for through body porcelain tile.

PEI ratings of glazed tile

Class 0. Suitable for walls only

Class 1. Recommended for wall use 
But may be used both on interior walls or bath floors without direct access to outdoor elements.

Class 2. Suitable for most residential floors 
May be used where abrasive foot traffic is minimal – such as bathrooms, bedrooms, dining rooms, living rooms, and sunrooms.

Class 3. Ideal for all residential floors
For floors subject to normal foot traffic and usage (including kitchens, outdoor entryways and hallways).

Class 4. Great for all residential and light-medium commercial 
Suitable for light to medium commercial applications. Will withstand moderate foot traffic in many commercial areas (commercial kitchens, hotel rooms, exhibition halls, etc).

Class 5. Great for all residential and most commercial 
Ideally suited for all residential and most commercial applications under normal foot traffic conditions (shopping centers, hotel foyers, walkways, and industrial applications). For very high traffic areas, consider and unglazed through-body color porcelain, which does not carry a PEI rating.

Mohs scale 
Frederick Mohs invented this geological scale of minerals to rate scratch resistance from 1-10. Think of Mohs as Method Of Hardness Scale. This test is not an industry standard but it’s a great comparison to show the difference in scratch resistance between tile and other hard flooring materials.

Coefficient of friction (COF) 
The coefficient of friction rates the slip resistance of a tile. ADA recommends a test rating of .6 (wet or dry) on floors and .8 for ramps. However, common sense must prevail. If you are told that a shiny surface tile has a .6 rating, stop and think if that tile really will be slip resistant.

Breaking strength 
The breaking strength test is a good indicator of the chip resistance of a tile because it tests the strength and density of the bisque. Using applicable ASTM test, ceramic floor tile typically has a breaking strength of 250 lbs. This can be less for poor quality tiles, higher with porcelain tiles (up to 400lbs).

What do you want your tile to do? 
Facial surface. A slip resistant surface may be more difficult to keep clean. A glossy surface may show dust and be slick. 
Body strength. Chip resistance, frost resistance, breaking strength, and water resistance. Make sure that the tile face and the tile body meets both performance and visual expectations.

TRAVERTINE QUALITY RATINGS

Travertine is divided into four visual classifications. As with other natural stone products such as diamonds and precious stones, the value of travertine is based on the visual appeal, availability and rare qualities of the stone. As these are visual based categories, the durability or suitableness for a specific purpose are not part of this classification.

Commercial Quality 
Tiles with a commercial rating are divided into two distinct categories.

Class “A” is for appearance. The distinctive variation that occurs in an “A”. quality commercial stone may include a broad color range, a unique color range, usual mineral deposits or a moderate amount and size of fill. Class “A” commercial tiles will be of uniform thickness, squareness and size, but may have some variation in finish and fill color.

Class “B” is for dimension. Travertine tiles in this category may have variations in size or thickness, a considerable amount of fill or very large fill. These tiles are usually set with a 3/16” or larger grout joint.

Classic Quality A classic quality tile will be of a consistent size as to allow a grout joint of 1/8” or less. Classic tiles will have a moderate amount and size of fill. Classic tiles are sorted within a defined color range with minimal mineral deposits.

First Quality

First quality travertine tiles are sorted to have minimal fill and color variations within a defined range. First quality tiles have virtually no unusual mineral deposits and they are precision sized for minimal grout joints and ease of installation.

Premium Quality 
Premium quality travertine is so designated because of the unusually high density of the stone. This means that there are very few and very small holes. The face of a premium quality stone will be of discernible higher visual quality when placed next to other qualities of travertine