Because Pennsylvania Natural Slate is a very durable material, a finish is not necessary to protect the material. However, due to aesthetic considerations, a particular sealer, impregnator, oil, etc. may be required. In most cases, this will darken the slate to a gray-black. In the case of flooring, sealers / impregnators are required to protect the joints and to allow for easier maintenance of the floor. Window sills and stools are sometimes oiled to darken the slate and protect it from finger prints and water rings caused by vases or glasses. Oil is also applied to counter tops and vanities.
The following are general recommendations and are not meant to cover all installations. Final finishes are always left to the discretion of the Architect and Owner.

NATURAL CLEFT FINISH:

Slate supplied in a Natural (Split Face) Cleft finish can be finished with a stone sealer, stone impregnator, oil, wax, etc. Normally a sealer will result in a gloss or satin finish. Sealers and impregnators are normally used for exterior panels and interior floors. In residential flooring installations, a good acrylic floor wax may be sufficient. Boiled linseed oil, thinned with turpentine, is commonly used for interior window stools, counter tops and vanities.

MACHINE GAUGED FINISH:

Slate supplied in a Machine Gauged Finish may be oiled or waxed. Sealers will show application marks and should, in most cases, not be used on the Machined surface. Adherence of the sealer may also be a problem. Normally oil or wax is used to darken and protect the surface from finger prints, etc. As oil or wax can be renewed as often as deemed necessary, it is an easily maintained finish. Since this finish may be used for flooring applications, attention to "slip resistance" should be considered. Common uses of this finish are window sills, treads & risers.

SAND RUBBED FINISH:
Slate supplied in a Sand Rubbed Finish may be oiled or waxed. Impregnators and sealers may also be used, however depending on the type of sealer, application marks are sometimes visible. Spray application of sealers can alleviate this problem. Oil or wax will darken the color and produce a satin finish. These finishes are common to window sills, counter tops, vanities, fireplace facings, etc.

HONED FINISH:

Slate supplied in a Honed Finish may be oiled or waxed. Sealers will show application marks and should, in most cases, not be used on the Honed surface. Adherence of the sealer may also be a problem. Normally oil or wax is used to darken and protect the surface from finger prints, etc. As oil or wax can be renewed as often as deemed necessary, it is an easily maintained finish. Window stools, counter tops, vanities, fireplace facings, etc. are commonly oiled or waxed.

HAMMER-MILLED FINISH:

Slate supplied in a Hammer-Milled Finish can be finished with a stone sealer or impregnator. With the textured indentations, use of a wax or oil is not recommended.