Spalling
Contents |
[edit] Introduction
The word ‘spall’ refers to the breaking of a material into pieces, particularly cracks below the surface that cause part of the surface to come off.
In construction ‘spalling’ refers to the flaking, cracking, peeling, crumbling or chipping of concrete or brickwork, particularly where parts of the surface might be said to have ‘blown’ off. This can occur as a result of water penetration, heating (such as during a fire) or by mechanical processes. Spalling is typically caused by poor installation, poor maintenance, poor repairs, or by environmental factors.
Spalling can be inconsequential, that is, a purely aesthetic issue, or it can lead to serious structural damage requiring costly remediation work.
[edit] Concrete spalling
A common cause of spalling in concrete is the presence of moisture. This is a particular problem in basements, where moisture, often combined with salt, pushes out from within concrete. Striated lines, discolouring and coarse texture are physical signs of spalling.
Heat and mechanical pressure can result in uneven expansion of concrete and subsequent fracture. Particularly concrete that includes reinforcing bars, which absorb heat at a different rate and may expand or corrode. Applied heat may also release the water contained within the concrete.
Whether or not concrete will spall varies greatly and is dependent upon a number of factors, such as:
- The configuration of materials.
- Composition of the material.
- Temperature and temperature change.
- Local conditions.
- Length of time since curing (water content is higher in concrete that has recently been poured).
- Ability of the surface to absorb liquid.
- Expansion and contraction of the freeze/thaw cycle.
- Presence of chemicals such as de-icers and fertilizers.
Steps can be taken to prevent spalling when the concrete is first poured, as the mix of concrete will influence the likelihood of spalling in the future. Proper air entrainment should be assured, typically a minimum of 4% air in mixture, allowing for enough airspace within the concrete to accommodate water expansion.
The appropriate mix of sand, cement and aggregate should be achieved, as insufficient aggregate may result in a top layer that is weak and prone to spalling. The mix should be kept as dry as possible, as high water content can compromise the concrete’s strength, with the correct curing time allowed.
Action should be taken quickly if spalling is detected in concrete installations, as the risk of damage rises the longer remediation is delayed.
[edit] Brickwork spalling
Bricks will deteriorate through spalling as a result of moisture penetration, eventually resulting in the brick cracking. This can be a particular problem with softer, more absorbent bricks.
One of the most common causes of spalling in old, solid walled buildings is the use of cement pointing, over soft lime mortar joints. Interstitial moisture is lost primarily through the mortar joints - the lungs of the wall - and when blocked with cement, this moisture then tries to escape through the brick faces, blowing them.
Water is absorbed by the porous surface of bricks, and in cold periods, expansion by freezing can cause bricks to crack. Fluctuations in weather, humidity and temperature are a major factor, as even the slightest movement in the structure can leave holes in mortar through which moisture can penetrate to the brickwork. Very soft lime mortar will alleviate this problem, being highly porous, and it soaks up moisture, releasing it as conditions change. Other elements of the building can lead to similar problems, for instance, windows and gutters that leak, damaged chimneys, doors and windows and around the foundations.
Masonry sealants should never be used. They trap moisture and salts and exacerbate spalling. Alternatively, drainage installation around the building can help prevent water pooling near the foundation level, and repairing leaks and other defects can remove sources of dampness. Water splash from badly fitted gutters is a common cause.
If spalling has already occurred, damaged bricks can be replaced, but the cause of the moisture should also be identified and dealt with appropriately.
Crystallisation of salts just below the surface of bricks can also cause spalling. This is known as cryptoflorescence. The problem is often associated with magnesium salts. Cryptoflorescence is associated with a large build-up of salts and usually occurs where old, relatively weak, bricks are re-used inappropriately, particularly in areas of excessive dampness. It can also occur if the brickwork has been covered by a surface treatment because the salts may crystallise behind the treated surface and force it off.
[edit] Research
In February 2019, researchers from the University of Sheffield used fibres extracted from the textile reinforcement used in tyres to reduce concrete’s tendency to spall explosively under the intense heat of a fire. Ref http://www.constructionmanagermagazine.com/news/old-tyres-improve-concrete-fire-resistance/
See also: Palling.
[edit] Related articles on Designing Buildings Wiki
- Admixtures in concrete.
- Alkali-silica reaction (ASR).
- Basic brickwork replacement.
- Brick.
- Concrete.
- Condensation.
- Cracking and building movement.
- Damp.
- Damp proofing.
- Defects in brickwork.
- Defects in stonework.
- Diagnosing the causes of dampness (GR 5 revised).
- Efflorescence.
- Frost attack.
- Mortar.
- Mould growth in buildings.
- Palling.
- Penetrating damp.
- Reinforced concrete.
- Repointing.
- Rising damp.
- Rising damp in walls - diagnosis and treatment (DG 245).
- Settlement.
- Surfside condo collapse: climate change demands adaptation in design and approach.
- Wall tie failure.
[edit] External references
- Interfire - Spalling
- Pro Construction Guide - Spalling brick
Featured articles and news
Boiler Upgrade Scheme and certifications consultation
Summary of government consultation which closes 11 June 2025.
Deputy editor of AT, Tim Fraser, discusses the newly formed society with its current chair, Chris Halligan MCIAT.
Barratt Lo-E passivhaus standard homes planned enmasse
With an initial 728 Lo-E homes across two sites and many more planned for the future.
Government urged to uphold Warm Homes commitment
ECA and industry bodies write to Government concerning its 13.2 billion Warm Homes manifesto commitment.
From project managers to rising stars, sustainability pioneers and more.
Places of Worship in Britain and Ireland, 1929-1990. Book review.
The emancipation of women in art.
Call for independent National Grenfell oversight mechanism
MHCLG share findings of Building Safety Inquiry in letter to Secretary of State and Minister for Building Safety.
The Architectural Technology Awards
AT Awards now open for this the sixth decade of CIAT.
50th Golden anniversary ECA Edmundson awards
Deadline for submissions Friday 30 May 2025.
The benefits of precast, off-site foundation systems
Top ten benefits of this notable innovation.
Encouraging individuals to take action saving water at home, work, and in their communities.
Takes a community to support mental health and wellbeing
The why of becoming a Mental Health Instructor explained.
Mental health awareness week 13-18 May
The theme is communities, they can provide a sense of belonging, safety, support in hard times, and a sense purpose.
Mental health support on the rise but workers still struggling
CIOB Understanding Mental Health in the Built Environment 2025 shows.
Design and construction material libraries
Material, sample, product or detail libraries a key component of any architectural design practice.
Construction Products Reform Green Paper and Consultation
Still time to respond as consultation closes on 21 May 2025.
Resilient façade systems for smog reduction in Shanghai
A technical approach using computer simulation and analysis of solar radiation, wind patterns, and ventilation.