Stone veneer chimney repair by local pros in East Park

How deep to rake out stone joints

The National Park Service's Preservation Brief 2 sets the raking depth at 2 to 2 and a half times the joint width as a minimum, so new mortar bonds and stays put. For stone masonry with wide joints, that can mean several inches.

Loose or crumbling mortar beyond that depth also comes out. The brief shows new mortar falling out of a joint that was not prepared deeply enough. We rake to a sound depth and show you the prepared joints before filling.

• At least 2 to 2 and a half times the joint width
• Deeper where mortar is loose
• Square back so new mortar locks in

Filling deep joints a layer at a time

Where the old mortar came out more than about an inch deep, the brief has the deep spots filled first, packing mortar in layers of roughly a quarter inch and letting each reach thumbprint hardness before the next goes on. Most shrinkage happens as mortar hardens, so layering keeps it small.

Deep stone joints take several layers and more time. We price that time honestly, because a deep joint filled in one go shrinks, cracks away from the stone and lets water straight back in.

Brushing joints after tooling

After tooling, excess mortar at the edge of a joint can be brushed away with a natural bristle or nylon brush, according to the brief, which also says metal bristle brushes should never be used on historic masonry.

Metal bristles scratch stone and leave steel fragments that rust into stains. Our crew carries soft brushes for every stone job and brushes at the right point in the set, so the stone faces stay clean.

Moss, algae and dirt on stone

Shaded sides of a stone chimney can hold moisture long enough for moss and algae to grow in the joints and on the stone. The growth holds water against the surface and can darken the stone.

We start with the gentlest cleaning that works, water, a mild detergent and a soft or bristle brush, and avoid pressure and harsh chemicals on the stone and joints. Where growth keeps returning, the findings note the moisture that feeds it.

Water stains inside near a stone chimney

Stains on a ceiling or wall beside a stone chimney can come from the flashing, the cap, open joints or water behind veneer. The stain inside does not always sit directly below the entry point.

We check the outside of the chimney from the roof and the base, and the attic where it is accessible, to find the path. Leak repairs that are not stone work, such as flashing or cap work, are quoted on their own lines.