Field guide to facade defects

Thinner than 0.3 mm

Looks like

Fine lines under 0.3 mm wide in the render or coating, running in a net or at random. No step when you run a finger across.

Cause

Drying shrinkage of the coating or surface render; thermal movement. Usually does not reach the structure.

If left

Not urgent in itself. It is an entry point for water; over a few years it can widen and start corroding reinforcement behind it.

Urgency

Low

Next step

Monitor. Photograph the same spot every six to twelve months and compare widths. Fill at the next repaint.

AI

Detectable if it shows in the photo. Width cannot be measured from a photo; use a crack gauge on site.

0.3 mm or wider, deep

Looks like

0.3 mm or wider, running long and straight or diagonal. Typical: diagonal from window corners, horizontal at floor lines. A step or offset between the two sides is a bad sign.

Cause

Differential settlement, earthquake, structural deformation, or expansion from corroding reinforcement. May extend into the structure.

If left

Water reaches the structure, reinforcement corrodes and expands, and the concrete spalls. A crack that keeps widening is a structural problem.

Urgency

High

Next step

Have a qualified engineer or building surveyor look at it. Record the width over time. 0.3 mm is an industry rule of thumb, not a legal threshold, but it is where treatment changes.

AI

Detectable; wider cracks show reliably. Whether it is structural cannot be decided from a photo.

Detached from the substrate, not yet fallen

Looks like

Almost invisible. Sometimes fine cracks along grout lines, a slight bulge, or a hollow high-pitched sound when tapped (sound tiles give a dull thud).

Cause

The bond between tile and render, or render and structure, fails through thermal cycling, water and age.

If left

A lifted tile eventually falls. From height that is a casualty. This is why Japanese law requires periodic full-surface tap testing of tiled facades.

Urgency

High

Next step

Tap testing by a qualified surveyor; infrared survey for large areas. Protect the area below anything at risk of falling first.

AI

Not detectable from photographs as a rule. Bulges and grout cracks can be flagged as suspicion. No substitute for tap testing or infrared.

Tile, render or coating has come away

Looks like

Missing tiles with substrate showing; render detached in sheets; coating peeled back to the layer beneath.

Cause

Lift that has progressed to failure; for coatings, poor preparation or water behind.

If left

The exposed substrate takes in water and the surrounding lift spreads. The area around a loss is the next to go.

Urgency

High

Next step

Protect and restrict access below. Tap-test the surroundings. Repair only after the cause (lift, water) is dealt with.

AI

Detectable — one of the clearest defects in a photo.

White powder or white streaks

Looks like

White powder on the surface, white runs down the wall, white seeping from crack edges. Powdery to the touch.

Cause

Soluble compounds (calcium hydroxide and others) in the concrete or mortar, carried to the surface by water and set by air. In other words: a record of where water has passed.

If left

Harmless in itself. It is evidence of a water path, and downstream of that path are corrosion and delamination.

Urgency

Medium

Next step

Find where the water gets in — a crack above, joints, coping, sealant. Cleaning without closing the entry point brings it back.

AI

Detectable; white runs read clearly.

Brown or reddish runs

Looks like

Brown to red-brown streaks down the wall, usually from a crack edge or from the base of metalwork — railings, grilles, pipe brackets.

Cause

Reinforcement inside, or attached metalwork, is corroding and the rust is carried out by water.

If left

Rust from reinforcement expands and pushes the concrete apart from inside; spalling comes next. Rust from fixings weakens the fixing.

Urgency

Medium

Next step

Trace the source. If it is reinforcement, refer to a qualified surveyor together with any cracking. If it is a fixing, check that it is still secure.

AI

Detectable; distinguishable from efflorescence by colour.

Concrete broken out from inside, rebar visible

Looks like

A chunk of concrete missing with corroded reinforcement exposed; rust staining and radial cracks around it.

Cause

Corroding reinforcement expanding and pushing off the cover concrete. Common where cover is thin or water gets in: balcony parapets, canopy edges, around openings.

If left

Exposed bars corrode further and the loss spreads. A falling fragment is a casualty. This is a structural-capacity issue.

Urgency

High

Next step

Protect and restrict access immediately. Qualified survey and repair including corrosion treatment of the reinforcement.

AI

Detectable; exposed bars and losses read clearly.

Joint and window-perimeter sealant

Looks like

Fine surface cracking, hardened with no give, pulled away from one side leaving a gap, shrunk and sunken, torn.

Cause

UV and thermal cycling. Many products reach the end of life at around ten years; it varies widely by product, orientation and site.

If left

Water enters the gap and leaks inside the wall or around windows. It is the entry point for the other defects on this page.

Urgency

Medium

Next step

Replace (remove the old, fill new). Over-sealing on top only delays. Plan it with the major repair cycle.

AI

Cracks, gaps and pull-away in the photo are detectable. Loss of elasticity is checked by touch on site.

Powder on your hand

Looks like

Run a hand over the wall and coloured powder comes off. Gloss gone, colour looks faded.

Cause

UV breaking down the resin in the coating, leaving pigment as powder. The start of the coating's end of life.

If left

The coating stops shedding water and the substrate begins to absorb it. Precursor to cracking, peeling and algae.

Urgency

Low

Next step

Put repainting in the plan. Not dangerous now; each year of delay is paid for in the speed of the next defect.

AI

Not reliably detectable from photos; loss of gloss depends on lighting. Touch is definitive.

Green or black growth, dark streaks below windows

Looks like

Green to black film on north or shaded faces. Dark streaks running from below windows and canopy edges.

Cause

Moisture and dirt. Run-off staining is rainwater collecting dirt and taking the same path every time.

If left

Cosmetic in itself. A face that grows algae is a face that stays damp, and coatings age faster there. Streaks mark water paths.

Urgency

Low

Next step

Clean. If it comes back quickly, look at drainage on that face — drips, canopies.

AI

Detectable, reported as soiling with low severity.

Low morning or evening light throws bulges and steps into shadow; at noon everything looks flat. The day after rain, water paths stay as slow-drying streaks — the best time to trace efflorescence and rust staining to their source.

Photograph face by face, from the same distance and angle, so you can compare the same spot six months later. Deterioration shows in the difference between two photos more than in either one.

• AI facade inspection service →Upload photos; get these defects back with severity ratings.
• 日本語版 — 外壁劣化の見分け方 →The Japanese guide, with the Japanese statutory context.