What Should You Record About Concrete Voids, Rust Stains and Spalling?

Record which concrete element is affected, its location, safely taken photographs and when damage was first reported. Keep construction, loading, water-exposure and repair records so original voids or cover issues can be distinguished from later change. Preserve specialist survey locations and access limits, separating visible spalls from suspected separation. These records support appraisal; they do not establish cause or remaining capacity.

For an on-site assessment of a specific building concern, explore our forensic site inspections. An article cannot determine the cause or appropriate solution for an individual property.

Honeycombing concerns voids in concrete; exposed reinforcement means steel is visible. Spalling means pieces of the surface or protective cover have broken away. Cracks and spalling need a cause-led appraisal before a repair is chosen. The same visible damage can arise through different mechanisms, so a photograph alone cannot establish whether reinforcement corrosion, concrete deterioration or structural movement is responsible.

Was the condition present when the concrete was cast?

Voids, honeycombing and exposed reinforcement can be construction-quality concerns. Placing and compaction need to limit material separation or loss, fill the formwork, remove entrapped air and closely surround reinforcement and other embedded components.

Cover is the concrete between reinforcement and the surface. Required cover relates to compressive strength and exposure classification, so the applicable detail needs the element's design and exposure context. Insufficient original cover, voids present as cast and cover lost later need different evidence. Steel can remain concealed where cover is insufficient; exposed steel alone does not establish what cover was originally provided.

Look for available photographs taken during construction or when formwork was removed, along with concrete placement and inspection records. Compare those with the first report of damage and any later repairs. That history helps the engineer separate what is known about original construction from later change; a present-day photograph cannot supply the missing history.

One appearance, several possible causes

Reinforcement corrosion is one important possibility. Carbonation can reduce the concrete's alkalinity that protects embedded steel, while chlorides can promote corrosion even where that alkalinity remains high. Expanding corrosion products can crack and dislodge the surrounding cover.

That is not the only explanation for a spall. Other possibilities include poor-quality concrete, chemical attack and frost attack. Restrained shrinkage and moisture changes are among the possible causes of cracking. These are alternatives to investigate, not diagnoses to select from appearance.

Even rust marks need context. Spots associated with iron compounds in aggregate or remnants from formwork differ from stains associated with embedded reinforcement or tying wire. The investigation should test that distinction.

Read the defect in its structural setting

The location and structural role of the damage change the investigation. A defect on a beam, slab or small bearing projection is considered with its reinforcement, supports and loading history. Cracking near supports, excessive deflection and damaged bearing details call for different checks; they are not a set of homeowner crack-width limits.

The photograph below shows beam reinforcement exposed where cover has been lost. It illustrates the condition needing assessment, not proof that corrosion explains every spall. The photograph does not establish remaining capacity or the necessary repair.

Drawings can help identify the intended reinforcement and structural arrangement, but selected details may need checking because actual construction or later alterations can differ from the recorded design.

Lost concrete cover and exposed beam reinforcement.

Choose tests to resolve a question

Tests should distinguish the plausible explanations. A covermeter can estimate reinforcement position and cover, but its readings need skilled interpretation and may require verification. Carbonation testing addresses a different question about the concrete's alkalinity. Neither result by itself establishes the whole member's condition.

Where corrosion is suspected, a half-cell survey indicates corrosion risk; it does not measure how much damage has already occurred. Core examination and microscopy may investigate concrete quality or deterioration. The engineer must plan intrusive work so that sampling does not significantly weaken the structure or damage reinforcement.

Map separation as well as missing concrete

A delaminated area is a layer of concrete that has separated, even if it has not yet fallen away. A professional delamination or drummy survey can help detect separation and developing spalls over reinforcement. A trained professional may find relevant areas beyond the outline of concrete already missing. This is not a task for an owner to undertake by striking a suspect surface.

Keep the survey findings tied to locations on a drawing or sketch, with photographs and the limits of access recorded. Distinguish visible spalls, areas indicating separation and areas not assessed. Such a map helps define the next enquiries, but it does not by itself show chloride distribution, remaining steel section or the member's capacity.

Exposure can also make a small-looking location important. Even in good-quality concrete, chlorides can produce concentrated pitting and severe local section loss at a crack crossing reinforcement, with little outward evidence elsewhere. A short affected length is therefore not a measure of the seriousness of steel loss. Direction and appearance need the material and exposure context.

Repair follows the appraisal

Before choosing a patching system, the appraisal needs to establish the relevant material condition and whether loading, support or detailing also contributes. Restoring the visible surface does not by itself resolve those uncertainties. A repair specification should follow that assessment rather than assume all damaged concrete needs the same treatment.

What changes when steel is exposed?

Controlled exposure during professionally planned work may reveal that a bar has lost section or developed pits. A structural engineer must assess its residual structural capacity: retaining and repairing the existing reinforcement, replacing a damaged part or providing supplementary strengthening are engineering decisions, not choices settled by how clean the steel looks.

The repair specification can provide for those decisions to be made as reinforcement is revealed. Ask who will inspect the exposed condition, what record will identify the affected bars and locations, and how the resulting decision will be authorised before the evidence is concealed. Photographs of a finished patch cannot recover that information afterwards.

The assessment also concerns the structure during the work. Removing damaged concrete can change the condition of a member before reinstatement, so the professional guidance calls for structural stability and necessary capacity-maintaining measures to be resolved. A repair that restores the cover's shape does not, on its own, establish that lost steel capacity has been restored.

These reinforcement-preparation provisions expressly concern non-prestressed steel. They must not be transferred into a plan for exposing, cutting or modifying prestressed or post-tensioned reinforcement. The construction type and any uncertainty about it belong in the professional brief.

If the revealed condition extends beyond the anticipated area, keep the revised extent and engineering decision linked to the original survey. Record what was found and what was accepted before reinstatement, without treating newly exposed damage as automatic proof of its cause or of responsibility for it.

If fragments could fall or damage is progressing, seek prompt engineering advice and avoid the affected area. For an immediate threat to safety, contact emergency services. Do not remove loose concrete, expose steel or drill to investigate it yourself.

Useful next steps

• From a safe position, record which element is affected and photograph the surrounding structure as well as the damage.
• Gather drawings and available records of loads, water exposure and earlier repairs for the engineer.
• Ask which possible mechanism each proposed test will investigate and what uncertainty will remain after it.