Installation Diagram - Interior Flooring
Basic Specification  

See Photo Interior Flooring

The Care of Slate Floors


Slate Flooring (Interior) - 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 3/4" 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 (3/8" 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 1/8" 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 1/8" 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 1/4", 3/8", & 1/2" 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. 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.

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  • The Structural Slate Company
    222 East Main Street
    P.O Box 187
    Pen Argyl, Pennsylvania 18072-01
    1.800.67.SLATE or Fax: 610-863-7016
    ssco1@ptd.net