Stone and brick foundation waterproofing in Jersey City

Walk into the basement of a brownstone in Hamilton Park or Van Vorst Park and you'll often find walls of rough fieldstone or old brick, laid thick, with soft mortar between the pieces. Those walls were built with lime mortar, which is meant to be softer and more porous than the masonry around it. It lets moisture move through and evaporate, and over a century of wet seasons it slowly washes out. What's left are open joints, sand on the floor and a wall that seeps across its whole face.

These foundations also sit on some of the wettest ground in the city. Downtown Jersey City and Hoboken were largely built on marsh and fill near the Hudson, and the water table there rises after long rains. Add a front areaway with a small drain under the stoop, and sometimes a vault under the sidewalk, and you have several ways for water to reach a wall that was never designed to be watertight. Our areaway and stoop work often goes hand in hand with foundation repairs.

Where joints have washed out, the wall needs new mortar, but the wrong mortar does real harm. Modern cement mortar is harder and less permeable than old stone and brick. Packed into a lime-mortar wall, it traps moisture in the masonry instead of letting it pass through the joints. The water then exits through the brick or stone face, which can crumble and spall. We repoint old foundations with a lime-based mortar that's softer than the masonry, so the joints stay the sacrificial part of the wall.

The work itself is patient. Our crew rakes out loose mortar to a sound depth, cleans the joints, dampens the masonry and packs new mortar in layers, tooling it to shed water. On rubble stone, joints vary in width and depth, so this is done by hand. The same principle applies above grade; our brick repointing page covers walls and facades.

We also check what's behind the joints. In places where stones have shifted or a section of brick has lost its bond, the wall may need stones reset or bricks rebuilt before repointing makes sense. Where the wall bulges or shows a clear lean, we ask for a structural engineer's view before doing anything else. Most rowhouse foundations, though, are sound under their washed-out joints, and once repointed they carry the house the way they have since the day they were built.

A common shortcut is to coat the whole basement wall with cement parging, waterproof paint or a thick sealer. On a poured concrete wall that can sometimes help. On a stone or brick foundation it usually backfires. The coating traps moisture in the wall behind it, salts build up under the surface, and within a few seasons the coating bubbles and sheds, often pulling the face of the old brick with it. Many of the crumbling walls we see were damaged by a well-meant coating, not by the water itself.

We'd rather let the wall breathe and manage the water. Repointing restores the joints. Then a dimple membrane is hung in front of the wall, not glued to it, with an air gap behind it. Water that still seeps through the stone runs down that gap into a drain at the base. The masonry can dry toward the gap, the room stays dry, and nothing is sealed against the old wall.

Humidity is the last piece. Even with the joints repointed and a drain in place, an old stone basement holds more moisture in the air than a poured one, especially in summer, when it can sit above 60 percent relative humidity. A dehumidifier set to keep the room around 45 to 55 percent discourages musty odors and lets the masonry dry steadily behind the membrane. We size it to the basement and drain it into the sump or a floor drain so nobody has to empty a bucket.

Most rowhouse foundation jobs end with an interior drain along the base of the stone walls feeding a sump with a battery backup. Old stone foundations often have uneven footings or none at all in the modern sense, so we dig carefully along the base and avoid undermining the wall. The membrane laps into the drain stone, and the slab is re-poured over it.

Party walls deserve special mention. In attached rowhouses, the foundation along each side is shared with the house next door, and it can't be dug out from outside. Water may enter from a neighbor's yard, leader or areaway, so we point out any source we can see on the other side. Exterior work on the front of a house in a designated historic district goes through the Historic Preservation Commission review, and we tell you up front when a job will likely need it.