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Salt damp

Ground moisture wicks up through stone and old brick, carrying salts that crystallise and blow the plaster and mortar apart at skirting height.

What is actually happening

Pre-1960 walls were built without a damp-proof course, or with a slate or bitumen one that has failed. Moisture rises by capillary action, evaporates at the surface and leaves salt behind. The salt is the damage: it fretts mortar, bubbles paint and turns render to powder in a band 300-1,200mm above the floor. Adelaide's inner and western suburbs are the national capital of it; Melbourne's brick terraces and bluestone footings have their own version.

The signs

•A tide mark or bubbling paint in a band above the skirting
•Powdery white crystals on brick or stone
•Mortar you can scrape out with a key
•Skirting boards soft or rotten at the back
•A musty smell in rooms on the ground floor, worst after rain

Read the damp and movement tells like an inspector

The proper fix

A chemical damp-proof course: drill and inject a silicone cream into the mortar bed at floor level, then strip the salt-laden plaster back to bare wall, let it dry, and replaster with a salt-retardant render. Sometimes an undercut physical DPC on stone. Fixing the source (leaking gutters, garden beds against the wall, paving above floor level) is half the job and often the forgotten half.

What it costs, South Australia

Salt damp treatment (chemical DPC)$350 – $750

Render crack repair and patch$600 – $2,500

Internal repaint (3-bed, walls, ceilings, trims)$6,000 – $13,000

Indicative 2026 ranges, not quotes. All costs

When to walk away

Rarely. Salt damp is common, predictable and fixable. Walk away when it has gone untreated so long that the stone itself is fretted deep, or when a "fix" was painted over without a DPC: the next round of plaster fails in 2-3 years.

Where it turns up

Suburbs in our street DNA set whose era mix and soil make salt damp a regular. Not a survey; a pattern.

Victoria · 7

Brunswick Carlton Fitzroy Footscray Hawthorn Richmond St Kilda

Questions

Is salt damp covered by insurance?+

Almost never. It is classed as gradual deterioration, not a sudden event. Building inspection reports will flag it and lenders sometimes ask for a quote before settlement.

Can I just paint over salt damp?+

You can, and it will bubble again within a year or two. Paint traps moisture and makes the wall worse. Treat the damp course first, replaster with a salt-retardant system, then paint.

The other villains

Restumping and reblocking Reactive clay and cracked walls Asbestos in the eaves, walls and fence The leaking shower

Insider reading

Reading the inspection report on an older house

Reading the paperwork

How to read a building inspection report

The builder skips to the summary of major defects, then searches the document for the words "further investigation", "unable to inspect" and "safety hazard". Everything else is maintenance.

Read the guide

Reading the site

How to walk a block before you buy it

A supervisor stands at the front boundary and looks at the ground level against the footpath, then walks to the back and looks at the fences. If the neighbour on the high side has a retaining wall and the one on the low side does not, you are about to pay for one.