Maintaining Baltimore's stone foundations; its not so hard after-all.
Baltimore has several building characteristics that make it unique. The Baltimore Bull-nose casing around windows, the Height and beauty of our historic buildings rooflines, and our crumbling stone foundations.
Stone foundation with repair
As the bull-noses get covered with aluminum and the rooflines are simplified for economy the stone foundations cannot be easily replaced. These foundations are a mosaic of Baltimore history, some of the oldest buildings in our city are built from ballast stone shipped across the sea set upon foundations of cobblestone and granite. The red stone that marks some of our oldest buildings is likely from the Seneca Quarry; supporting these historic homes is a stone foundation. This is so common a characteristic Baltimore has a historical district named the "Stone Hill Historic District" along the Jones Falls after an expansive group of buildings comprised of granite.
As time passes the mortar holding all the stone in place drys and crumbles to the touch. Maintaining these foundations is not as difficult as some would lead us to believe. If you are lucky your stone is unpainted. Stone is extremely porous and needs to breath from the inside to allow it to dry between rain fall. If your foundation is leaking look to ways to remove water from the foundation area through gutter systems instead of sealing the water into the wall using products that stop it at the interior.
Lets look at some repair methods:
1) You spray down the wall to minimize dust, and remove any failing mortar as deep as 3 inches.
2) Clean away any dust or debris still in the crevices of the wall.
3) Use type S mortar with a bonding agent to allow the mortar to stick to the stone.
4) Push your mortar as far in to seal it as best you can. replace any stone that has fallen away or was unseated when you removed the mortar.
*5) If you would like a smooth surface with color don't paint or cover the stone. Consider parging the surface with a dyed lime based mortar. This will give you a smooth surface, and because parging breaths it will help to maintain the stone and mortar. It is labor intensive but, is generally more cost effective then framing, hanging drywall and painting.
Stone foundations are beautiful and if you have one; I consider you lucky as you own a piece of history.