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 bands. A ribbon may be wide, narrow or even double.
In a facia panel, there may possibly be more than one ribbon. (Note:
Although Ribbon grade is not recommended for exterior use it can
be very suitable for interior installations.) Ribbon slate is supplied
in Machine Gauged, Sand Rubbed or Honed 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. 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.
- Hone & Arris Edge is a honed edge and either a
1/8" chamfer or a 1/8" radius on the top front 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 front edge without honing the front edge. Sawn Edges
are edges directly from the saw and are usually very smooth and
sharp as they are cut with a diamond saw. Quirk Mitre Edge is
usually used at exterior corners. Other Edge Profiles are
subject to availability of tooling and should be investigated prior
Exterior / interior panels are usually supplied in 1",
1 1/4", 1 1/2" and 2" thicknesses. Other thickness
are available to comply with special field conditions.
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. Oiled Finish is usually a mixture of 50%
Boiled linseed oil and 50% turpentine. This is suitable for all
facial finishes and is normally only used on an interior application.
Since slate is very dense and non-absorbing, a finish is only required
to facilitate easier maintenance.