Parging is the coating applied to the visible (above-grade) portion of your home’s foundation walls. It is applied to both poured-concrete and concrete-block foundations to hide surface imperfections, marks from formwork and the like, so its role is essentially decorative. A parge coat is not a requirement under the Building Code, but it does have another useful purpose: it acts as a barrier against inclement weather. That’s no small benefit to Quebec homeowners!
It’s a different story for foundation walls with exterior insulation. In this case, application of parging over an armature or other rigid finish material is a must, to protect the insulation from impacts as well as sunlight.
Types of parging
There are two types of parge coatings: cement and acrylic. The table below compares the main features of each.
| Cement parging | |
|---|---|
| Composition | Two main mixes:
|
| Characteristics |
|
| Acrylic coating | |
|---|---|
| Composition | System consisting of:
Texture varies depending on the aggregate used in the mix. |
| Characteristics |
|
Conditions for parging application
The following conditions must be respected to ensure successful foundation parging:
- Surface must be free of stains and any brittle material.
- Surface must be moistened before application of the mixture.
- Mix must be prepared according to the manufacturer’s instructions.
- Application and curing temperature (at least 5°C) must be respected.
- Parging must be periodically moistened during the curing period.
For a foundation wall with exterior insulation, either mix can be used, but the following condition must be respected: a metal armature or fibreglass panel must be anchored through the insulation into the foundation cement before applying the parging. The upper portion of the insulation must be covered with flashing, i.e., a membrane that will prevent water infiltration.
Can parging be repaired? Yes
Parging can be repaired in many cases. Inspect your parging periodically; if superficial cracks appear, seal them quickly to prevent water infiltration, which is likely to cause more significant damage.
Limited damage, such as minor cracks, small areas of detached material or nicked corners, are easily repaired by a professional, who will use quick-setting cement to complete the job of resurfacing in one day. Resurfacing involves applying a thin parging coat to restore a uniform surface.
If there are severe breaks, the old parging should be removed and a completely new coat applied. A damaged or uneven area can also be covered in a metal armature, with parging applied over top to even out the surface.
Can parging be painted? Yes, but…
Some contractors may offer to refresh the surface of your foundation parging using smooth or textured paint. Before opting for this solution, keep in mind that:
- a watertight finish can trap moisture and accelerate deterioration of the parging underneath.
- if you aren’t happy with the results, or you want to sell your home and potential buyers don’t like the painted foundations, it will be difficult to undo the job: new cement won’t adhere well.
If the parging has been painted and you want to change it, the options are to:
- remove the paint coat with a wire brush or grinder and then re-parge.
- anchor a metal armature into the foundation and cover it with a new parging coat.
- remove the existing parging along with the paint and re-parge.
