Block & Stone Foundation Repair · Kitchener

Stone and Block Foundation Repair in Kitchener

A stone foundation is not failing because it is old. It is failing because the mortar has washed out and nobody has put any back in eighty years. Most of them can be kept. Some of them have to be rebuilt in sections. The difference is a screwdriver in the joints.

The houses built in Kitchener before about 1930 — the brick and frame houses downtown, on the streets of Cedar Hill, around Victoria Park, along Queen Street South and in the older pockets of Waterloo near uptown — mostly sit on rubble-stone foundations. Fieldstone and split limestone laid in lime mortar, two feet thick or more, sometimes with a cut-stone outer face, always with a rubble core. From the 1920s into the 1950s the same neighbourhoods and the first ring of suburbs around them went to early concrete block, thinner, on shallow footings. Both are structural walls that have carried a house for the better part of a century and will carry it for another, if the problems are dealt with while they are still repairs.

How stone foundations fail

• Mortar loss. Lime mortar is soft on purpose. Water running through the joints over decades washes it out, until you can push a screwdriver into a joint to the depth of your hand. The stones are then held by weight and friction alone.
• Loose and displaced stones. Once the mortar is gone, stones in the outer face work loose, especially under beam pockets and at corners. Some fall out into the basement.
• Bulging. A section of wall, usually below grade on the side that takes the most water, moves inward as a unit because the rubble core has lost its bond. This is the stone equivalent of a bowing block wall and it is the sign the wall is running out of time.
• Rotten sills and joist ends. The wood sill plate sits directly on damp stone. Floor joists rest in pockets in the wall. Both rot, and when they do the floor above drops and the wall loses the plate that ties it together at the top.
• Hard cement parging. Somebody in the 1960s or 70s coated the inside of the wall with a hard Portland cement parge. It cracks, it hides what is behind it, and it traps water in the wall where it does the most damage. It often has to come off before the wall can even be assessed.

Repointing

Where the stones are sound and in place, the repair is repointing: raking the old mortar out of the joints to a proper depth, cleaning them, and packing in new mortar in lifts. The mortar matters. A lime-based or lime-rich mortar that is softer than the stone lets the wall move and breathe the way it was built to. Hard modern cement mortar in a soft stone wall pushes the movement into the stone, which then spalls and cracks. It is slow work by hand, done wall by wall from the inside and, where the outside is exposed above grade, from the outside too.

Rebuilding sections

A bulged or collapsed section is taken down and relaid. The floor above is supported first on temporary posts and beams, the loose section is dismantled stone by stone, the rubble core is cleaned out, and the section is rebuilt in the same stone, bedded properly, with a bonded core. Sections are kept short — the house is never unsupported along more than a short length — and the work is sequenced like underpinning. Where a stone wall has lost too much to rebuild in stone, a section can be rebuilt in block or poured concrete tied into the stone on either side.

Liner walls

For a stone wall that is sound enough to stand but too rough or too weak to be trusted alone, a reinforced concrete or block liner wall can be built against the inside face, tied to the stone with anchors and bearing on its own footing or on the widened base of the old wall. It gives the house a new structural wall without dismantling the old one. It also costs floor space, and it is the point at which a waterproofing contractor usually wants to put a drainage layer behind the liner, which is their trade, coordinated but separate.

Sills, joist ends and beam pockets

Rotten sill plates are replaced in sections with the floor supported: the old plate is cut out, the stone under it is levelled and capped, a new pressure-treated plate is set on a moisture break, and the joists are re-supported on it. Rotten joist ends are cut back to sound wood and sistered, or the joist is re-bearded on a new ledger. Beam pockets are cleaned out, the stone around them rebuilt, and the beam set on a proper bearing plate rather than bare stone.

Early block foundations

Block foundations from the 1920s to 50s have their own list: mortar joints deteriorating, blocks spalling where they have been wet and frozen for decades, and shallow footings that have let the wall settle at a corner. Deteriorated blocks are cut out and replaced, joints are repointed, and a wall that has settled is dealt with as a settlement job, with piering or underpinning under the affected section.

Heritage districts

A good part of Kitchener's stone-foundation housing is inside a heritage conservation district or on the city's heritage register. Foundation repair below grade rarely changes anything the street sees, but work on an exposed stone face above grade might, and the City of Kitchener is the place to check before that part starts.

What this page is not

A damp stone basement is normal and is not, on its own, a structural problem. Keeping water out of it — exterior membranes, weeping tile, interior drainage, sumps — is a waterproofing contractor's work. This page is about the wall standing up. The two often get done together, by two trades.

Frequently asked questions

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