i would just clean it with an acid wash. I use Vanatrol from prosoco, it is a sensitive brick cleaner. Have cleaned a lot of limestone steps with it. It not as harsh as muriatic, We removed brown stains like those recently from carerra on an old building, fast and simple. I wouldnt think that limestone would require honing..ya never know though.

From: Roger Konarski <qm144@yahoo.com>
To: Stone and Tile PROS Technical Support <sccpartners@stoneandtilepros.com>
Sent: Friday, August 24, 2012 6:07 PM
Subject: [sccpartners] fire place hearth

 
I have been asked to service a limestone fire place hearth. Please see attached picture. I was thinking about apply a hydrogen peroxide poultice. Then honing the surface. Appreciate any suggestions.