Installation Diagram - Exterior Paving
Basic Specification  
See Photo: of Exterior Paving
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Slate 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 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. (Uniform joint allowance of a minimum 3/8" 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 3/4"-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.

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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