Installation Diagram - Treads & Risers
Basic Specification
See Photo - Tread & Risers  

Treads and risers may be an exterior or interior application. Slate for exterior use should conform to A.S.T.M. C-629 for Class I slate and interior applications may be Class I or Class II.

Clear Grade - Clear slate is free of Ribbons and most markings. It is a blue-gray to blue-black color and if sealed or otherwise treated, it is approximately "jet-black". Clear slate is supplied in Natural Cleft, Machine Gauged, Sand Rubbed or Honed finishes.

Ribbon Grade - Ribbon slate is characterized by an ornamental dark band which, in the case of treads & risers, usually runs parallel with the length of the treads & risers. A ribbon may be wide, narrow or even double. In a wide width, there may possibly be more than one ribbon. (Note: Ribbon grade is not recommended for exterior use.) Ribbon slate is supplied in Machine Gauged, Sand Rubbed or Honed finishes.

Face Finishes - Natural Cleft Finish is a rough textured, split face finish. The bottom is gauged to an even plane and the thickness, although varying due to the facial deviation of the cleft, is constant within the maximum thickness specified. (NOTE: The facial deviation in Natural cleft finish may appear more pronounced with regard to the front edge plane of a tread.) Machine Gauged Finish is a smooth, even finish which approaches the honed finish. However, slight swirl marks are usually visible. Sand Rubbed Finish is a smooth, even finish with a slight stipple equal to about 80 grit sand paper. Honed Finish is a smooth, satin finish equal to about 240 grit.

Edge Finishes - Hone & Arris Edge is a honed exposed edge and either a 1/8" chamfer or a 1/8" radius on the top exposed edge to remove the sharpness. This may be specified in conjunction with any of the facial finishes, however in the case of Natural Cleft finish, the 1/8" radius is normally used rather than the chamfer. Arris Edge is the 1/8" chamfer or 1/8" arris on the top exposed edge without honing the edge. Sawn Edges are edges directly from the saw and are usually very smooth and sharp as they are cut with a diamond saw. Bevel & Nosed Edge is a somewhat standard edge for treads. Other Edge Profiles are subject to availability of tooling and should be investigated prior to specifying.

Thickness - Treads and risers are supplied in 3/4", 1", 1 1/4", 1 1/2" & 2" Thicknesses. Other thicknesses are available to comply with special field requirements.

Treatments - 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. Since slate is very dense and non-absorbing, a finish is only required to facilitate easier maintenance. NOTE: Care should be taken when specifying any finishes for a walking surface. Walking surfaces should be as slip-resistant as possible.

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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