"Slate 101" Thinking outside of the Ceramic Box and thinking about what's inside the Slate Tile Crate

"Slate 101"
Thinking outside of the Ceramic Box
and thinking about what's inside the
Slate Tile Crate By Graeme Bruce

You've all seen the books called Computers for Dummies (I am almost finished it ... and can't understand a damed thing) - well here's my rendition of Slate for Dummies (no offence intended).

Throughout history, stone has always been regarded as the most durable and beautiful of building materials. It's true even today. In particular, centuries old slate is enjoying a popular resurgene as the perfect natural stone for building. It is capable of transforming any area inside or out to one of timeless beauty and an affordable price. One of the earliest examples of roofing slate is on the old Saxon Chapel at Stratford-On-Avon, England. Built in the eighth century, the chapels' slate roof remains in good condition today. In France, at Angers, there is a slate roofed castle that was built in the twelfth century. The first authenticated description of quarrying of slate, dating to about 1750.

But, I digress, let's get down and dirty with the dirt on slate ... Mud. Yes mud! Let's face it, when we see a beautiful slate installation, we are looking at mud - mud that is over 500 millions years old. Imagine being over 500 million years old and just be of age to show your beauty. Shale and slate begins with mud. Some say that over a thousand million years ago, vast areas were completely covered by the seas. Sediment of clay caused by ground up rocks was carried with the movement of these seas and deposited in layers of mud on the sea floor. Shells of marine animals and wind blown dust from volcanoes sank and were buried in the mud. Pressed down by its own weight and that of the water the mud solidified into mud stone, a tough structure less substance (by the way this is soapstone). If the bed was very thick and especially if deep layers of sandstone or limestone were deposited on top of it by another sea it was compressed and covereted into a soft rock called shale. Shale like sandstone and limestone is a sedimentary rock. Slate is a metamorphic rock. It was formed by a bed of shale which, deeply burried, was subjected to heat and enormous pressure when the earths crust shrank, folded and mountains were created. As a result the slates minerals were rearranged and straight lines of cleavage developed at an angle to the original bedding, so that it is easily split into layers. Are you with me so far? Ok, now we have slate. Mud to mudstone, mudstone to shale, shale to slate. Sedimentary to metamorphic. So now we have a fine grained rock when sedimentary rocks such as shale are metamorphosed by great pressure. Wham - we have slate. In the formation of slate, pressure causes the flaky minerals within the sedimentary rock such as mica, clay and chlorite to be re-oriented; the flat faces of the minerals lie at right angles to the source of pressure, and the planes of easy cleavage are also at right angles to the source of the pressure.Slate is intermediate in hardness between mica, schists and shale. Now, with over 100 natural colours available we ask ourselves where the heck does the colour come from? The colour of slate is determined by its chemical and mineralogical composition. Hematite is responsible for purple, chlorite for green, grey and black to carbon and graphite while iron oxides can add a variety of colours. Shades of red and tan are related to iron oxides.

Ok - now we are on a roll - let's carry on....

It's hard to tell just how many slate colours are out ther but reputable dealers will carry about 80 different natural colours. Where can we use this stuff? Well, slate can be used everywhere. Both interor and exterior like walls, roofs, floors, decks, shower enclosures - you get the picutre - it can be used virtually anywhere. Why use slate - natural non slip surface, will last forever, easy to decorate around and is a good conductor of heat (warmer than a ceramic floor). Slates come in all different formats from tumbled to borders, sawn edge tiles to hand chipped edge tiles, profiles to be polished and honed, mesh mounted mosaics to roofing. Slabs are also available and make excellent counter tops and vanities. Slabs come in both natural cleft and honed surface. Something for every place residentially or commercially.

Just a few important installation tips when installing slates - always lay out slates before setting so that a good colour mix throughout the floor is obtained. Wipe dust off the backs of the slate tiles before installing. This gets rid of the slate dust which will act as a bond breaker. Slates typically are not square so grout joints should be around 1/4" wide. This will compensate not only for a slightly different sizing but also help in obtaining a smooth floor. All slates should be sealed after installation (some even apply the sealer after installation but prior to grouting - the sealer will then act as a grout release). Only use premium sealers - this will give you long life, non yellowing and will not produce a slippery surface. Do not seal too soon after installation - we don't want to seal in moisture. Those premium sealers allow for sealing just 48 hours after installation is complete because they allow vapour transmission. Ensure that adequate control joints are put in. Because slate is a good conductor it does tend to move more than the average ceramic tile installation.

And last but not least of all - always buy from a reputable dealer/importer. They know which slates are freeze/thaw stable, which slates can be used commercially etc. When I went to school we used slates in wooden frames, bound with red yarn, and slate pencils that would screech and make the teacher mad - boy, have we every come a long way since then.