Slate flooring is normally installed over a concrete slab, wood sub-floor or existing flooring.

Mortar Bed Setting on Slab:

1. The slab should be clean and free of all debris. If any curing compounds were used, scarifying may be necessary.

2. Wet down or dampen the slab, however do not allow standing water or puddling.

3. Spread a bed of approximately ¾″ thickness mortar mix consisting of 1 part Portland cement and 3 parts mason’s sand (1:3 mix).

4. Tamp slate firmly into setting bed until the desired level and uniform plane are met.

5. Remove any excess mortar.

6. Carefully lift slate and butter the back with a paste of neat Portland cement.

7. Tamp slate back into place.

8. Joints (⅜″ minimum joint is recommended) should be filled and pointed with a 1:2 grout mixture, preferably on the same day of installation.

Thin-Set Mortar:

1. The slab should be clean, free of all debris and smooth finished. A variation in level should not exceed ⅛″ in ten feet.

2. Apply dry-set Portland cement mortar or latex-Portland cement mortar with a trowel over an area of which slate can be applied while mortar remains plastic.

3. With a notched trowel, comb mortar to an even setting bed, being careful not to scrape mortar from slab. Bed thickness should be approximately ⅛″ with no bare spots.

4. Slate should be placed with a slight twisting motion and tamped level to finished grade and uniform plane. (A minimum contact of 80% is required. Larger pieces should be “back buttered” to obtain maximum possible bond. In wet areas, a 100 % contact bond is required.)

5. Care should be taken to achieve joint allowance with a minimum amount of adjustment.

6. Joints should be grouted with the specified grout after setting bed is dry.

Thin-Set Mastic:

1. The slab, sub-floor or existing floor should be clean and free of all debris. Existing sub- floor should be solid and free of any loose material. Painted or otherwise treated surfaces should be sanded with coarse sand paper.

2. With a “vee”-notched trowel, spread the specified mastic being sure not to leave any bare spots. Spread only an area that can be comfortably reached to install the slate.

3. Slate should be pressed firmly into the mastic, but not tamped. Joint allowance should be obtained with as little disturbance as possible.

4. Allow mastic a minimum of 24 hours drying time before grouting joints.

5. Grout joints with a latex grout or as specified, sponging the slate frequently to remove excess grout.

Thickness – Interior flooring is usually supplied ¼″, ⅜″, and ½″ thickness with cleft face and the bottom gauged to allow thin-setting. The larger the sizes of slate tile, the more critical the level of the slab or sub-floor becomes.

Cleaning – Slate should be periodically sponged down during installation to prevent mortar stains from forming when using grouted joints. Water should be kept clear and clean by changing often. After slate has been set for at least 14 days, it should be scrubbed with an approved detergent, followed by a thorough rinsing with clean water. After rinsing, slate should be wiped with soft toweling or a chamois. Tough mortar stains that have set can be removed with muriatic acid and water (1 part acid, 10 parts water), however, care should be taken as the grouted joints are vulnerable to the acid.

Maintenance & Treatments – Although the slate needs no sealer or other treatment, the joints are susceptible to minor cracks and separations. Use of a sealer / impregnator is useful in protecting water infiltration through these cracks into the setting bed. Sealers usually darken the slate and give a glossy appearance. Natural cleft finish and Sand Rubbed finish may be sealed suitably, however, sealers may not adhere nor give a desirable appearance to Machine gauged or Honed finish. Impregnators usually do not as radically alter the color of the slate and give a more satin finish. As with sealers, Machine gauged and Honed finish may not accept the application of an impregnator. NOTE: Care should be taken in selecting a treatment that is slip resistant.

Paving & Flagging (Exterior)

Slate paving / flagging is normally installed over a concrete slab of 4″ thickness.

Mortar Bed Setting:

1. The slab should be clean and free of all debris. If any curing compounds were used, scarifying may be necessary.

2. Wet down or dampen the slab, however do not allow standing water or puddling.

3. Spread a bed of minimum ¾” thickness mortar mix consisting of 1 part Portland cement and 3 parts mason’s sand (1:3 mix).

4. Tamp slate firmly into setting bed until the desired level and uniform plane are met. (Uniform joint allowance of a minimum ⅜” is recommended.)

5.. Remove any excess mortar.

6. Carefully lift slate and butter the back with a paste of neat Portland cement.

7. Tamp slate back into place.

8. Joints should be filled and pointed with a 1:2 grout mixture or other approved material, preferably on the same day of installation.

(Attention should be given to predicted overnight temperatures. Freezing could harm the setting bed and joints.)

Sand Bed Setting:

1. The area should be excavated to remove topsoil for a depth of at least 10″ inches. (Additional depth may be required in areas where freezing normally causes ground heaving.)

2. Gravel and sand or other suitable base material should be installed and compacted at a thickness of 6″ inches.

3. Another 4″ inches of sand or modified fill should be installed and compacted to approximate final grade.

4. Lay slate on top of final fill and pneumatically tamp to final plane, allowing desired joint. (NOTE: A fixed border is usually required to restrict movement of the perimeter.)

5. Spread sand on slate and broom diagonally across joint lines to fill.

6. Lightly wet down area and fill any settled joints.

Thickness – Exterior paving is usually supplied ¾”-1″ thickness with cleft on both faces. Thicknesses over 1″ are available to comply with special field requirements.

Cleaning – Slate should be periodically sponged down during installation to prevent mortar stains from forming when using grouted joints. Water should be kept clear and clean by changing often. After slate has been set for at least 14 days, it should be scrubbed with an approved detergent, followed by a thorough rinsing with clean water. After rinsing, slate should be wiped with soft toweling or a chamois. Tough mortar stains that have set can be removed with muriatic acid and water (1 part acid, 10 parts water), however, care should be taken as the grouted joints are vulnerable to the acid.

Maintenance & Treatments – Although the slate needs no sealer or other treatment, the joints are susceptible to minor cracks and separations. Use of a sealer / impregnator is useful in protecting water infiltration through these cracks into the setting bed. Sealers usually darken the slate and give a glossy appearance. Natural cleft finish and Sand Rubbed finish may be sealed suitably, however, sealers may not adhere nor give a desirable appearance to Machine gauged or Honed finish. Impregnators usually do not as radically alter the color of the slate and give a more satin finish. As with sealers, Machine gauged and Honed finish may not accept the application of an impregnator. NOTE: Care should be taken in selecting a treatment that is slip resistant.

Care of slate floor

Because “Natural Slate” is practically immune to all common chemicals, it is probably the least exacting of floors in the matter of maintenance. Any of the usual cleaners may be used on slate with safety, though strong alkaline solutions or acids may affect the grout joint. Being dense and practically non-porous, slate is not affected by strong detergents or ammonia.

Synthetic Detergents

To maintain a slate floor, it should be kept clean like any other floor, scrubbing as necessary and mopping between times. To scrub a cleft floor, use a strong solution of floor detergent. Spread it over the surface and let it stand for several minutes. Then, with fresh solution, scrub with a stiff brush under a floor machine. Abrasive powders are less desirable as they sometimes leave residue. After the slate has been thoroughly cleaned, rinsed and allowed to completely dry, it will benefit from the application of a protective treatment. The word “protective” is not to imply that the slate needs protection, but that a coat of wax, sealer or impregnator will allow it to be cleaned easier in the future.

Sealers / Impregnators

Slate, supplied in the standard “natural cleft” finish may be sealed or have an impregnator applied. The sealer best adapted for slate should be of low viscosity and less than 25% in solids. The new impregnators also work very well, however, any treatment should be applied strictly in accordance with the manufacturer’s recommendations. Impregnators usually do not create a gloss finish, whereas sealers may be a gloss or satin finish. Care should be taken to assure that the slate as well as the grout joints are totally dry and the floor clean prior to application. Dampness in the joints can cause treatments to turn white. Most all sealers and impregnators are a permanent treatment and are very difficult to remove. A sample piece or small area should be treated first to assure that this is the desired end finish.

Waxes

The water waxes and resin finishes will serve better on interior surfaces since they seldom hold up satisfactorily on outdoor surfaces. Sometimes they turn gray from exposure and are difficult to remove. The solvent waxes are less affected by the exposure, but since they must be buffed when dry, they present a problem on a natural cleft surface rather than a smooth surface. For interior slate, either kind of wax will emphasize the colors and make sweeping and dusting much easier.

Dust and ordinary soil will adhere less tenaciously to a waxed surface and often dry buffing will avoid the need for mopping or scrubbing. If soil on the waxed surface resists buffing with a brush, fine steel wool or an abrading pad may be used. Care should be taken not to dig into the wax if possible. Some of the acrylic waxes are very good on natural slate. For interior slate, any of the self polishing water waxes or one of the emulsified resin finishes may be best suited as they do not require buffing after drying.

Traffic Patterns

Most heavy use areas will eventually develop “traffic patterns”. It may appear that the slate is wearing, but more often than not it is the finish. Waxes can be stripped and reapplied, however some sealers are relatively permanent. A record of the finish and manufacturer should be kept as some sealers are not compatible with others. The original manufacturer may be contacted for recommendations for re-sealing or removal of the finish.

Slip Resistance

Care should be taken when applying any finish to slate as well as any stone to preserve “slip resistance” on commercial projects. A stone’s slip resistance can be greatly altered by the application of any finish. While this is extremely important on commercial floors, it is also desirable in the home. All floors are slippery when wet and the use of some finishes may compound the problem.