It’s a young tree- it is infested badly with something that is a solid covering, rough in texture, light grey in color and resembles rough cement, and is difficult to scrape off with a finger nail–what is it and how do I get rid of it? and what do I treat it with?
Ginkgo Trees are generally resistant to disease and pests.
Weather can effect the barks of the trees and slugs are know to eat the leaves.
Honey Fungus also can be an issue with Ginkgo Trees.
Your description does not suggest any of the above known issues.
Is the issue on the bark or leaves of your tree?
If the leaves are covered, I would take a sample to your local County Extension Office.
They may help in identification. Images can also be taken to the office.
Here is a link to help locate your closest office.