Bond test before quoting
We tap and scrape to find out what the old coat is actually holding onto.
What parging over poured concrete requires
On a formed wall, prep is the entire job.
Laitance removal
The weak, dusty skin on a formed face is taken back to sound concrete.
Form release residue treatment
Oily film from the forms is degreased or abraded off, never coated over.
Tie hole and snap tie patching
Each hole is cleaned out and packed with a non-shrink repair material.
Bonding agent or mechanical key
Slurry bond coat or a scarified surface, depending on what the wall needs.
Our Process
Our poured concrete parging process
1
Send photos or book a look
Close-ups of any peeling edges tell us a lot.
2
Test the bond
Hollow-sounding areas and sheet peeling get mapped before pricing.
3
Open and clean the surface
Laitance off, release residue off, tie holes packed.
4
Key in and coat
Bond coat, then the parge coat worked hard into the surface.
Why poured concrete rejects a parge coat
Form release film
The oil or wax that let the forms strip cleanly also stops cement from ever gripping the face.
Laitance skin
The fine cement and water that rises against formwork dries into a weak layer that peels away with whatever sits on it.
Open tie holes
Unpacked snap tie holes stay wet, then push the coating off from behind as they freeze.
Why parging over poured concrete is a bonding problem
Ottawa Parging Experts approaches parging over poured concrete as one question with several parts, and the question is always the same: will this coat actually hold onto the wall. On a formed foundation, adhesion is not one factor among many. It is the whole job, and every early failure we get called out to on poured walls comes back to it.
The reason is density. Poured concrete placed against plywood or steel forms comes out of those forms hard, smooth, and close to non-absorbent. A cement parge coat sticks to masonry mainly by being drawn into an open, thirsty surface and curing inside it. A formed wall offers very little of that. The mix sits on the face, cures into a competent layer of its own, and then, one or two winters later, comes away in flat sheets with a clean back.
Poured foundations are the standard on Ottawa homes built from roughly the 1980s onward, and on most infill and rebuild work across the city. So this is the substrate on the majority of newer walls, and it is the one where a fast, cheap coating job fails fastest.
Form release agents and laitance before parging over poured concrete
Two specific layers sit between fresh parging and sound concrete on a formed wall, and both are invisible from a few metres away.
The first is form release. Forms are treated with oil, wax, or a chemical release agent so they strip cleanly off the cured wall. That film transfers onto the concrete face and stays there. It does exactly what it was designed to do, which is stop cementitious material from sticking, and coating over it guarantees the coat lets go. On a wall that has been in the ground for decades, weathering has usually reduced it, but in sheltered areas under overhangs it can still be present. Degreasing, pressure washing with the right detergent, or mechanically abrading the face all deal with it.
The second is laitance. When concrete is placed and vibrated, fine cement particles and water rise toward the form face and dry as a thin, weak skin. It looks like sound concrete and it is not. It has almost no tensile strength, so anything bonded to it is only bonded as well as that skin is bonded to the concrete underneath, which is barely at all. Removing laitance means grinding, scarifying, or washing the face back until you are into the aggregate-bearing concrete.
Once the surface is clean and open, we either create a mechanical key by abrading it or apply a bonding agent, or use both on walls that came out of the forms particularly smooth. A slurry bond coat scrubbed hard into the face, followed immediately by the parge coat while the slurry is still active, is the most reliable way we know to attach new material to dense concrete.
Tie rod holes and snap tie patches under parging over poured concrete
Formed walls carry a grid of small round holes where the ties that held the forms apart were snapped off after the pour. On most Ottawa foundations they sit in regular rows, and they need handling on their own terms.
An open or poorly patched tie hole is a direct path for water into the wall. Water that gets in there does not drain, it sits. In an Ottawa winter, with industry estimates for this market putting annual freeze-thaw cycles at 50 or more, that trapped water freezes and expands repeatedly, and it pushes outward on whatever is covering it. The result is a ring of cracked or blown-off parging around each hole, which is a distinctive pattern once you know to look for it.
Proper treatment means cleaning each hole out to sound material, then packing it with a non-shrink cementitious repair mortar rather than smearing parging across the opening. A tie hole filled with the same thin coat that goes on the rest of the wall will shrink, hollow out, and reopen. Any snap tie patch already on the wall gets tested the same way, and hollow ones get cut out and redone.
What parging over poured concrete costs in Ottawa
The pricing bands are the same as our other foundation work, but where a poured wall lands within them tends to be driven by surface preparation rather than by area. A spot repair runs $300 to $600. A moderate repair, meaning a wall section stripped back, prepped, and rebuilt, runs $600 to $1,500. Extensive repair or a full recoat runs $1,500 to $6,000. Coating a full perimeter is billed by the linear foot at $15 to $30, putting a 150 linear foot house in the $2,250 to $4,500 range.
A wall with sound, open concrete and tight tie patches sits at the lower end. A wall carrying old paint, a failed sealer, or a coat that is peeling in sheets sits higher, because removal and surface opening take the hours.
Work runs spring through fall, since the material needs above-freezing temperatures to cure, and Ottawa's frost-free season is about 158 days. Done onto properly prepared concrete, a parge coat should run roughly 10 to 25 years. Done onto laitance, it can fail inside two. If you are seeing sheet peeling with a smooth clean back, send us a photo. We will give you a straight read and a written quote within 24 hours.
Poured concrete parging questions
My parging peeled off the foundation in large flat sheets. What causes that specifically?
Sheet peeling with a clean back face almost always means the coat never bonded. On a formed wall that points at laitance or leftover form release film. The coating cured fine, it just cured on top of a layer that was never attached to the concrete.
What are the small round patched circles in rows across my foundation?
Those are snap tie holes, left where the steel ties that held the forms apart were broken off after the pour. They are normal. They matter for parging because a hole that was only smeared over will hold water and push a coating off from behind.
Do you need a bonding agent on every poured wall?
Not on every one. If the face is rough, clean, and open, a well-worked slurry coat or a dampened surface can be enough. If it is smooth, sealed, or shows any oily sheen, we either abrade it to create a mechanical key or use a bonding agent, or both.
Why does prep matter more on poured concrete than on block?
Absorption. Block is porous and pulls the mix into itself, which creates a grip almost automatically. Formed concrete is dense and low-absorption, so there is nothing for the coat to key into unless prep creates it.
Can old paint or a sealer stay on the wall under new parging?
No. Paint, waterproofing membrane, and clear sealers all break the bond, and a new coat is only as attached as the layer beneath it. Those come off first, or the wall is scarified back to raw concrete.