Parging a Basement Wall From the Inside: When It Helps and When It Won't

Most people think of parging as the cement coat on the outside of a foundation, and most of our parging jobs are exterior. But a lot of older Baltimore houses also have parged basement walls on the inside, over stone, brick or block. When that inside coat starts flaking, crumbling or turning white, homeowners want to know if it can simply be redone. Sometimes it can. Sometimes redoing it would be wasted money until something else is fixed first. If you are new to the term, start with what parging is.

What Interior Parging Is For

On the inside of a basement wall, parging gives a rough stone or block wall a flatter, cleaner surface. It fills voids, covers deteriorated mortar joints and makes the basement easier to keep clean and to paint. What it is not is waterproofing. A cement coat on the inside of a wall does not stop water that is pushing in from the soil outside.

Signs the Inside Parging Is Failing

• Flaking and spalling, where the surface comes off in chips or sheets and piles up at the base of the wall.
• Hollow areas that sound different when tapped, where the coat has let go of the wall behind it.
• White, chalky crust, called efflorescence. That is mineral salt left behind when water moves through the wall and evaporates on the inside face.
• Peeling paint in sheets, often with damp or powdery material behind it.

The Water Question Comes First

Almost every failure on the inside of a basement wall comes back to moisture. Water moving through the wall carries salt that crystallizes behind the parging and pushes it off. If the water keeps coming, new parging fails the same way, often within a few seasons.

So before interior parging, look at the outside of the house:

• Downspouts that dump right next to the foundation instead of several feet away.
• Gutters that overflow or leak at the corners.
• Soil, mulch or a patio that slopes toward the house instead of away.
• Failing exterior parging or open cracks on the outside of the same wall.

Fixing drainage is often cheap and makes the biggest difference. If water is actively coming through the wall during storms, or there is standing water on the floor, that is a job for a waterproofing contractor before any parging.

When Interior Parging Is the Right Fix

Interior parging makes sense when the wall is basically dry, or the moisture is light and the outside has been addressed, and the old coat is loose, flaking or patchy. It is also common when a basement is being cleaned up to be used: a laundry area, storage or a workshop.

How the Work Is Done

1. Remove what is loose. All loose and delaminated parging comes off, down to sound material. Leaving weak material behind means the new coat lets go with it.
2. Clean the wall. Salt crust and dust are brushed off so the new material can bond.
3. Fill voids. Holes and deep spots are filled with a cement-based compound and built up flush with the rest of the wall.
4. Finish coat. A skim over the repaired areas, or the whole wall, gives one even surface.
5. Let it cure before painting. If you plan to paint, choose a product made for masonry that lets the wall breathe.

A Recent Example

This summer we repaired the parging on the basement walls of a house off Roland Avenue in north Baltimore (21210). The old coat had come loose in several areas. We removed all of the loose and delaminated material, filled the voids with cement-based parging compound flush with the wall, and finished with a skim coat so the repaired sections and the old wall read as one surface. More examples are on our Towson parging page.

Basement walls flaking or turning white? Send a photo to (443) 806-8077 and we will tell you whether parging will help or whether the water needs to be dealt with first.