Parging and foundation surface repair

Parging is the thin mortar coat on the part of your foundation that shows above ground. It is there to tidy the appearance of block or concrete, to shed water and to give the wall a sacrificial layer that takes the weather instead of the structure. Most Ottawa homeowners notice it when it starts falling off in sheets after a hard winter.

Understand what the damage is telling you. Parging that is spalling, hollow-sounding or crumbling is sometimes only cosmetic, weathered by thirty freeze-thaw cycles a year and road salt off the driveway. Sometimes it is a symptom. Parging that keeps failing in the same spot usually means water is getting behind it, from a downspout, a hose bib, a deck ledger, a window well or grading that slopes toward the house. Recoating without finding the water source buys you two or three years.

Step one: sounding and removal. The whole exposed face is tapped. Anything hollow comes off, because new mortar bonded to loose mortar fails at the same speed. This step often exposes more than the homeowner expected, and it is also where you find out whether the concrete or block underneath is sound, deteriorated or cracked.

Step two: repairing what is underneath. Spalled concrete is cut back to solid material and rebuilt with repair mortar. Open block joints get repointed. Cracks are dealt with on their merits, which may mean injection from inside if they are more than surface deep. A crack that runs through the wall does not get parged over and forgotten.

Step three: preparation and bonding. The surface is cleaned and dampened, and a bonding agent or a scratch coat is applied so the new material grips. Parging applied to a dusty, dry or frozen surface will let go, and that is the single most common reason a parging job fails within two winters.

Step four: the coat itself. Mortar is applied in one or two coats to a total thickness usually in the 6 to 12 mm range, worked to a consistent finish and feathered into the grade line. Where it meets the ground it should stop cleanly rather than being buried, because buried parging wicks moisture. Fresh mortar needs to be kept damp for several days to cure properly, which matters more than most homeowners realize.

How long it takes. A single wall is typically half a day to a day. A full perimeter on an average house is two to four days including cure time between coats. Weather sets the schedule: mortar should not be applied in the rain, in direct hot sun that dries it too fast, or when temperatures will drop below about 5 degrees Celsius before it cures.

What it costs in Ottawa in 2026. Indicative ranges. A patch repair of a failed area is commonly $300 to $900. Re-parging one wall generally runs $800 to $2,500, and a full perimeter on an average detached house is often $2,000 to $6,000. The drivers are the height of exposed foundation, how much of the old coat has to come off, whether the wall beneath needs rebuilding, access, and whether any scaffolding or window well work is involved.

What makes an Ottawa house different. Ottawa runs through freeze-thaw repeatedly each winter and again during the spring melt, and the Building Code requires foundations in clay here to sit as deep as 1.2 m below grade for frost (OBC 9.12.2.2), which means there is often a substantial exposed section on a sloping lot. Two local details: road and sidewalk salt carried by splash and snow clearing attacks mortar along driveways and front walls, so the driveway-side wall almost always fails first. And in the older core, where a parged wall may be covering rubble stone rather than block, removing failed parging can expose a wall that needs repointing rather than recoating, which is a different and more skilled job.

Who should do the work. Parging is not a licensed trade in Ontario. It is masonry work, and the difference between a coat that lasts fifteen years and one that fails in two is almost entirely preparation and curing. Check liability insurance and WSIB coverage, ask to see a job the contractor did three or four years ago rather than last month, and be wary of anyone who wants to skim over loose material to keep the price down. If sounding the wall reveals structural cracking or a bowing wall, stop and get an assessment from a licensed professional engineer, verifiable in the PEO directory.

What to ask before you hire. How much of the existing coat are you removing, and how do you decide. What mix or product are you using, and is it suited to freeze-thaw. Are you using a bonding agent. How will you cure it and for how long. What happens at the grade line. Is there a warranty and what voids it. And the one that matters most: have you looked at where the water is coming from, because if you have not, this will fail again.

A last note. Parging is not waterproofing, and a fresh coat on a wall that leaks internally has hidden a problem rather than solved one. If your basement is wet, deal with that first and parge afterwards.