Julie Somis of Baltimore has a historic, brick, end-of-group rowhouse next to Riverside Park in South Baltimore. The basement of the house is unfinished, with a thin concrete floor and a low ceiling.
When she and her husband bought the house 11 years ago, their home inspector showed them deteriorated bricks and mortar at part of the foundation wall in the basement. The mortar is soft in places, the result of dampness in the wall leaching minerals from the mortar over the past century.
Moisture has also broken down salmon bricks - bricks that are unusually soft because they were not well-fired when they were originally baked in the brick kiln. As a result, some of the joints between bricks are missing some of their mortar, and the exposed faces of certain bricks have crumbled, leaving a shallow cavity in the face of the foundation wall at each deteriorated brick.
Repair of the walls hasn't been a high priority. The condition of the foundation is typical for a house of its type and age. The walls are thick, consisting of two or more 4-inch widths - parallel brick walls, back-to-back and joined together as they were built. So the loss of some mortar and a handful of crumbling bricks at the inside surface of the wall did not severely compromise the wall.
Repair of the foundation has made its way to the top of the "to do" list, and Julie has inquired about the methods and materials required to repair the wall. She and her husband plan to parge the surface of the walls in the basement to repair the deteriorated bricks and mortar.
Parging is the application of mortar to the surface of a masonry wall. The result is a form of stucco, or cement-based plaster. To apply it, mortar is troweled onto the wall and spread over the surface in a thin layer. Once it sets, it will serve to replace the missing mortar in the face of the wall, helping to stabilize the wall, and also will retard the passage of moisture through the wall.
The first step should be to clean the wall. Scrubbing with detergent and water using a stiff bristle brush will remove loose mortar, soot and grime, to ensure that the parging will bond well to the wall.
The wall should be rinsed with water as each section is cleaned. Bricks that have eroded deeply should be chiseled out and replaced with new bricks. Each new brick, and the surrounding bricks, should be misted with water before buttering the brick with mortar and sliding it into place.
Mortar can be prepared from scratch, using Portland cement, lime and sifted sand, but it is simpler to buy prepared mortar mix that only requires the addition of water. Starting with a small amount of the mix in a mortar pan, clean water should be added, a little at a time, and mixed in. A hoe or shovel can be used to mix it. Add water until the mortar will just hold its shape when you carve a V-shaped furrow through it.
Prepare the section of wall to be parged by misting it with water. This is important to keep the wall from absorbing moisture out of the mortar and causing it to dry too fast. If the mortar dries too fast, it will be soft and crumbly.
Apply mortar using a mason's trowel. Load the trowel with mortar by turning it over and scooping mortar onto the bottom of it. Use a sweeping motion as you spread the mortar on the wall, moving upward, and applying gentle pressure to force mortar into the contours of the wall. Parge the wall to a thickness of about a quarter-inch over the brick, lapping the edge of each stroke over what you've already done.