My sandstone exterior walls are crumbly

My sandstone exterior walls are crumbly Images

My sandstone exterior walls are crumbly

My sandstone exterior walls are crumbly Description

I recently purchased an 80 year old Cotwald Style Stone (http://g603.net) cottage in Louisville KY. My exterior walls are sand (http://maplered.com) Stone (http://g603.net) . Upon close examination I noticed the outer layer of Stone (http://g603.net) is very easy to break off and (http://maplered.com) crumble. In some places you can break of fairly large chunks.
 
Is there anything I can do to save my house?