Module 1 · Introduction to Damp

1.4 Common Symptoms of Damp

7 min read

Symptoms are your raw evidence. Before you pick up a meter, a careful visual and sensory inspection will usually have narrowed the field to two candidates. This lesson covers what to look for and — just as importantly — how to record it so it still means something when you write the report a week later.

Learning objectives

By the end of this lesson you will be able to:

Identify the visual, physical and environmental signs of damp.
Interpret what a symptom's location and shape suggest about its mechanism.
Distinguish active moisture from historic staining.
Record symptoms in factual terms that will survive scrutiny.

Key terms

Staining: Discolouration left by moisture movement or by dissolved material carried and deposited by it.
Mould: Fungal growth on a surface that has stayed damp. Needs sustained surface moisture, which usually means condensation.
Efflorescence: White, powdery salt deposits left on a surface as moisture evaporates and leaves dissolved salts behind.
Tide mark: A roughly horizontal line marking the height moisture repeatedly reaches before evaporating.
Hygroscopic: Able to absorb moisture from the air. Salts left by past damp are hygroscopic and keep an area feeling damp long after the source has gone.

Moisture changes materials in fairly predictable ways, and the changes accumulate. That gives you a rough timeline: fresh condensation leaves droplets and spot mould; months of it leaves staining and blown paint; years of it leaves soft plaster and decayed timber. Reading severity as duration is a useful instinct.

It also means symptoms outlive their causes. A stain is a record of moisture that was there, not proof of moisture that is there now. Separating live problems from historic ones is one of the most common judgement calls you will make, and one of the easiest to get wrong.

Visual symptoms

Dark or uneven patches on walls and ceilings, sometimes with a defined edge.
Paint blistering, bubbling or flaking; wallpaper lifting at the seams.
Black spot mould, typically in corners, along skirtings, behind furniture and around window reveals.
White powdery efflorescence on plaster or masonry.
A horizontal tide mark, with or without a salt band along it.
Rust staining or corrosion on fixings, radiator brackets and nails — a good sign of sustained moisture.

Physical changes to materials

Where the visual signs tell you moisture arrived, physical damage tells you it stayed. Check by touch and by careful probing where it is safe and non-invasive to do so:

Plaster that sounds hollow when tapped, or crumbles under light pressure.
Timber that has swollen, cupped, softened or darkened — skirtings, joist ends, window sills, door frames.
Floor coverings lifting, adhesive failing, or vinyl trapping moisture beneath it.
Insulation that has slumped or compacted where it has been wetted.

Physical damage nearly always means months or years, not days. It also raises the question of whether anything structural is affected, which is your cue to consider escalation rather than diagnosis.

Environmental and sensory indicators

Some of the strongest evidence is not visible at all. Use your nose and the back of your hand:

A persistent musty or earthy smell — often the first sign of moisture in a void, under a floor or behind a fitted unit.
Walls that feel cold and slightly clammy compared with an internal partition in the same room.
Condensation forming regularly on glazing, or standing water on sills.
A room that is noticeably harder to heat, or that feels cold despite the heating being on.
Windows kept shut, trickle vents closed, or an extractor fan that is disconnected or silent.

Location, shape and timing

Where a symptom sits and what shape it takes is usually more diagnostic than what it looks like close up. For each symptom, record:

Height above floor level, in millimetres, not "low down".
Whether the upper edge is a straight horizontal line or an irregular blotch.
Its relationship to features — a window, a corner, a chimney breast, a pipe run, an external downpipe.
Which elevation it is on, and whether that elevation is the weather-facing one.
Whether it changes with the season, the weather, the heating, or a particular activity.

A straight horizontal edge at 600mm on a ground-floor external wall means something quite different from an irregular patch at 1,800mm beside a window. Both are "damp on a wall" in a photograph.

Common mistakes to avoid

Photographing the mould and nothing else, losing the context that makes it interpretable.
Treating any stain as an active problem without checking whether it is currently wet.
Skipping the smell test, which frequently finds moisture no visual sweep would.
Recording "damp patch to wall" with no height, extent, elevation or shape.
Confusing efflorescence, which is salt from within, with mould, which is growth on the surface.

Lesson summary

Damp announces itself through visual change, physical deterioration and environmental cues. Severity broadly indicates duration, and symptoms outlive their causes, so distinguishing active from historic moisture is a core judgement. Location, shape and timing carry more diagnostic weight than appearance — and all of it needs recording in measurable terms at the time, not from memory afterwards.

In Lesson 1.5 we look at why so many of these symptoms get read wrongly, and how the industry's standard mistakes are made.