Question
Hi Marc,
We are working with a a landscaping firm to landscape/hardscape the exterior of our new-contruction home.

We are planning on using a blue-gray slate for the exterior patio and courtyard area.  It will be installed over a concrete pad.

I have recently heard that within about 5 years, slate can start to chip or sliver, leaving potato chip size remnants that must constantly be cleaned up.

The home is located in southern California.  

Can you provide us with any insight on using slate as an exterior hardscape?  For example, do you even recommend using it?  
--If so, is there anything we should make sure is done when it is installed?  
-- Is there any specific type of slate or location of the quarry that is better than others?  
-- And finally, what's your viewpoint on whether we should seal the slate?  

Many, many thanks Marc!

Answer
Installation over a concrete pad is excellent! It is difficult for me to convince clients that this is the preferred method, as cost becomes a factor, for something that is "unseen", structurally.  In the long run, it will cut down on loose pavers, potential cracks, etc.  It is a fine, rich product that has been used for literally centuries.

*NO* - I have not heard about "flaking" of young slate.  It can, after prolonged exposure to freeze/thaw, but in So. Cal., that isn抰 a big problem...mostly a Midwest/east coast thing.

Here is a website with more general info - http://www.vermontstructuralslate.com/applications/exterior-paving

As it is a natural material, it will have variations in color, density, etc. (like marble, granite, etc.)  And, you get what you pay for.  Quarried slate will last for quite a longtime...very durable stuff.  As a roofing material, it is second only to metal/copper in durability and longevity.

As far as sealants, some like the "wet" look that is achieved with sealants.  It is more than aesthetic.  There are some available, but I wouldn't do it unless it is to be installed in a driveway situation (or greasy BBQ area) where there is the potential for oil or tire-wear stains.  

Watch out for unevenness when installing, to avoid "trip & fall" hazards at the joints. Installing or "floating" the tiles in mortar will help this potential problem.

IF you are to install a polished variety (as compared to a "riven" or split type), I would really take care to not seal it, as this would make it even more slippery when wet.

Hope it helps ~M