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Slate Uses and History


Slate is no longer in the domain of chalkboards, pool tables, and roofs; it has moved in to the North American market for cladding in a large way. With it’s variety of colours and textures, slate is a stone consisting of wealthy tones, natural ridging, and earthy looks making it a versatile stone used in many inside applications. Though, slate brings a number of technical and maintenance problems with it. These problems can be the pest of customers but shouldn’t be the end of slate in home building.

There is a two-fold problem with the material. The first issue comes down to what slate is and what is sold as slate. The second rests upon the common caretaker perception that all stone was created the same. Being thoughtful of these two issues will very much benefit your chooses on whether to purchase the stone, where to put the stone, and how to take care of the stone.

It is almost certainly best to explain what exactly slate is as compared to what it is perceived to be. The MIA Dimension Stone Design Manual (DSDM) Version VII defines slate as…a fine-grained, metamorphic rock exhibiting slaty cleavage, which allows it to be crack into thin sheets. It is a low-grade metamorphic rock formed from shale, which is a thin-bedded, fine-grained, clastic sedimentary rock compacted from mud of clay-sized silicate clay mineral.

This is indeed a detailed definition for geologists, but for laymen who do not need scientific jargon, slate is basically defined as compressed mud. Basically slate is formed by clay and shale minerals settling underwater which is compacted by the sheer weight of the body of water. Where and how slate is formed plays a big part in quality of material.

A lot of areas of the earth were covered in water as earth’s terrain changed over millennia’s. As a result, slate of different densities and textures can be found all over the place compressed near the earth’s crust. Cleaning and maintenance of your slate is dependent upon the stone’s geographic origin and local minerals that compose its makeup.

Why is this? Well, since no two stones are created the same, your slate floor, worktop, vanity top, island, or backsplash may or may not be permeable according to the exact mineral composition. You can have a tile and stone slate floor made up of four general colours and only one will be porous, or two of the four, or three out of the four, or all of them. This is only because no stones have equal minerals, nor is the amount of compaction going to be the same in its formation.

Think of it like building snowballs. The harder it is squeezed, the denser the snowball becomes. If you use wet snow, it will create a denser, heavier snow ball the more you compact it. The constancy is dependent on the type of snow fluffy, compact, slushy, and the amount of compaction. Being thoughtful of that slate differs in make-up from one location to the other even from within the same quarry depending on formation we appreciate that installation and maintenance needs to take into thought the properties of the slate at hand.

Slate is siliceous stone, making it resistant to acids found in lemons, alcohol, and cleaning products. These acids will not etch the surface making it ideal for kitchens. However, like soapstone, slate is prone to scratching, particularly around the edges and becomes weathered looking over time. These scratches can usually be visually removed with mineral oil or a Colour Enhancer. In some cases, sand paper will do the trick. On the other hand, some people like the look of the stone after naturally taking spoil, which gives it charm.

The real problem lies in what is being sold as slate, or commercial slate. The properties of some stones do not fall into the same category, yet is labelled as slate. Several quartzites are sold as slates and even sandstone and granite. When people see a cleft on a surface, they assume its slate. Differences in mineral composition mean stones with varying requirements.

Although I originally stated that slate is acid resistant, the real situation is a little more complicating. Since slate comes in a huge number of states and compositions, it is impossible to have a general rule that classifies all commercial slate as acid resistant. Slate typically is resistance to mild acids giving it a much wider choice of cleaning product than acid sensitive stones such as marble and limestone. It is an absolute necessity for customers to find out the maximum tolerance of their stones prior to actual cleaning to avoid problems. The best solution is to try out every stone that you plan on using for your floor or worktops before even fitting them. This is particularly true if you are using several types and colours to finish your project, as one could be extremely resistant while others are not.

Slate is gorgeous in its natural state. Yet, it is common exercise to use man made chemicals on it, which, according to a person’s taste, adds or takes away from the stones attractiveness. The need for sealing, coating and/or colour enhancing has become a well-liked choice for many.

Problems can arise with future maintenance when treating the stone with these chemicals. For example, after 20 years or so of being fitted, you tend to see a little other than the stone itself.  Its been coated several times with either a commercial acrylic sealer or the most awful acrylic products known to man, sold from the shelves of your local shops. Acrylics are really nasty to strip and will leave a white residue particularly in the clefts that will most likely never come off without a process that will spoil the finish.

Also on the softer slate finishes, you get a condition where coating will soak into some of the more absorbent areas and never come out. Not to state you also have the grout to contend with as it holds old waxes and looks unattractive. For these reasons, you should try to avoid coatings on a new installation of slate unless you will maintain the surface with these products on a regular basis.

Impregnating sealers and colour enhancers work well if applied correctly. Remember, though, if applied as a coating, your trouble will be even shoddier than the ones with acrylics-sealers and enhancers, which are not made to be stripped and re-coated. Colour enhancers offer the alternative of bringing back the fading from natural wear on the stone. As the traffic zones dull, a nice deep cleaning and application will bring it back.

There has been a marked boost in the use of slate for kitchen worktops over the past decade and a half. Due to its subtle appearance, architects and planners are particularly fond of the honed finish for slate countertops. Good hard slates are similar to granite and serve well as countertops, adding earthly colours that exude warmth and gives a real traditional feel to your kitchen.

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