I needed to create custom post types, where the administrator does not have read/preview/publish permissions. This is a requirement, since the client does not wish the administrator (outside the organisation) to have access to what is confidential information.
In the Access Control module, the administrator is automatically given all permissions and there does not appear to be any way to remove these.
Wanted to know if it is possible to remove post type permissions from the admin user.
You are correct True admins have all unrestricted access to the website.
What you need to do is to create what I would called a Super User which would function like an admin but you will be able to disable the post types that you dont want them to have access to.
To do this just create a new role and set it to Copy the Privileges from the default admin role. With this new sub admin role you can then disable the CPT that you don't want that role to have access to.