Parging: Complete Ontario Homeowner's Guide

What Is Parging?

Parging is a thin cement‑based coating applied to foundation walls (concrete or masonry). It provides a uniform appearance and a sacrificial protective layer that sheds incidental moisture and resists abrasion at grade.

Think of parging as a protective skin for the exterior surface. It is not a structural repair and it is not a stand‑alone waterproofing system. It complements proper grading, drainage, and any dampproofing or waterproofing strategy.

Parging vs Dampproofing vs Waterproofing

These terms are related but serve different purposes. Parging smooths and protects the surface. Dampproofing resists soil moisture migration. Waterproofing systems address liquid water and hydrostatic pressure and usually include membranes and drainage.

On concrete block (CMU), parging is commonly used as a preparatory base before applying dampproofing or waterproofing. On poured concrete, prep focuses on cleaning, tie‑holes, and crack treatment before coatings. Always follow current product instructions and local requirements.

Codes, Standards, and Local Requirements

Requirements vary by jurisdiction and by the approval of specific membrane systems. As a rule of thumb, unit masonry (like CMU) often gets a parge coat before dampproofing/waterproofing; poured concrete gets prepared for coatings without a parge layer. For heritage masonry, mortar composition and permeability matter—use compatible mixes and methods.

Materials and Systems

Typical mixes include cement‑lime mortar with fine aggregate. Modern polymer‑modified parging mixes improve adhesion and durability for thin lifts. Where movement or transitions are expected, alkali‑resistant mesh may be embedded. Dense or previously coated substrates may require approved bonding agents.

Special substrates like insulation/ICF use purpose‑made parging products designed for adhesion and impact resistance.

Substrates and Surface Preparation

Long‑lasting parging starts with prep: remove loose material, failed parge, paint, dirt, and salts; treat cracks, voids, and tie‑holes first. Dampen the surface (no standing water) to reduce rapid suction. Feathering onto adjacent areas requires a mechanical key and a clean, sound substrate.

Application Basics and Thickness

A two‑coat approach—scratch/leveling coat followed by a finish coat—produces a durable result. Follow product maximum lift guidance; multiple thin coats outperform one heavy coat. Protect fresh work from rain, freezing, and rapid drying during cure.

Integrating with Drainage and Coatings

Where membranes are required, parging typically precedes them. After cure, apply the specified dampproofing/waterproofing and, if used, a drainage/dimple board. Ensure terminations and penetrations shed water. Above grade, keep finished parging clear of soil and mulch.

Ontario Climate Considerations

Freeze–thaw cycling, road salts, and heavy spring runoff are tough on foundation finishes. Schedule work in suitable weather windows, protect during cure, and manage downspouts and grading to direct water away from the wall.

Common Failures and Diagnostics

Delamination (hollow‑sounding areas) points to poor prep, trapped moisture, or incompatible mixes—remove to sound substrate and re‑parge. Cracking can stem from movement, over‑thick lifts, rapid drying, or freeze during cure. Efflorescence and staining indicate moisture pathways that must be addressed upstream.

Maintenance & Lifecycle

Inspect annually and after hard winters. Seal small chips promptly to prevent water at the bond line. Keep grade and mulch below the finished height and maintain positive drainage. Avoid de‑icers contacting the parge surface; rinse splash zones in spring.

Costs & Scheduling: What Drives the Scope

Key drivers include surface area and condition, access and protection, finish texture, season/weather protection, and whether coating or drainage tie‑ins are included. Small touch‑ups are fast; full elevations need more prep, staging, and cure time.

DIY vs Professional

Experienced homeowners may handle small cosmetic patches. For widespread delamination, below‑grade scopes, or active moisture problems, get a professional assessment to avoid repeat failures.

Frequently Asked Questions