Routes for users and admins separation Laravel

I'm trying to separate user from admin and forbid access of user to admin section.

My directories structure is

resources/
  -views/
    --site/
      ---users/
      ---admin/

In web.php I've added this

Route::get ('/', ['uses' => 'HomeController@index']);

Route::auth();
Route::group(['middleware' => ['auth'], 'namespace' => 'users', 'prefix' => 'site/users'], function() {

   // users routes
});

Route::group(['middleware' => ['auth'], 'namespace' => 'admin', 'prefix' => 'site/admin'], function() {

   // admin routes
   Route::get ('/admin', ['uses' => 'AdminController@index', 'before' => 'admin']);
});

When I log as admin and tried to open http://ift.tt/1691lrz I've got

(1/1) NotFoundHttpException

Same happens with users.

I have column in database is_admin which I check and store in session during log in.

via Chebli Mohamed