There are many different types of roof slate across the countries these days and each with very different qualities and characteristics. Knowing the kind and age of your roof slate can prevent you from as small possible rip-off from repair to something as big as safety issues! 

To judge the quality of your slate, simply check the exposed surface:
– If it’s smooth or even shiny, congratulations you have got a green light! Smooth surface slates should be preserved. 

– If it’s crumbly or flaking, be cautious! These slates can be preserved too, but they are already undergoing deterioration. 

Notice that environmental conditions like storms and pollutions will also cause change to roof slate from time to time. 

The main types of existing older slates roof are:

  1. Shadow Grey Slate. 
  2. Purple Slate. This is a great highly-restorable Vermont slate. It remains its color throughout its life span and has a life expectancy of about 150 years. 
  3. Unfading Green Slate. Also an excellent Vermont nearly unwearable after 120 years and could last to around 200 years.
  4. Sea Green Slate. A hard slate from Vermont with an average life expectancy of 150 years. It is known as “fading” or “weathering” slate nowadays because it changes to light gray after it weathers.
  5. Pennsylvania Black Slate. Sorry, but it might be the bad news of your day.  It is a soft slate with life expectancy of 75-125 years but more susceptible to weathering and has a high rate of water absorption. Usually, they can’t be restored but replaced. 

Images’ source:

(Source: https://newworldoldstone.wordpress.com/ribbon-slate/ Accessed July 25th, 2020)

(Source: http://www.slateroofcentral.com/identify.html Accessed July 25th, 2020)

References:

  1. http://www.slateroofcentral.com/identify.html New World, Old Stone. Accessed July 25th 2020
  2. https://newworldoldstone.wordpress.com/ribbon-slate/, Slate Rood Central. Accessed July 25th 2020