An Engineer's Notes on... Masonry #1
- Charlie Ely
- Aug 27
- 6 min read
As a temporary works engineers, we very often receive calls from contractors, the public or other engineers to ask us to assess masonry structures that are showing potential signs of damage or movement. But if you've dealt with masonry before then you'll know that this isn't a case of making a simple assessment... it requires a solid understanding of the material, as well as the structure that is affected.
In this short series of blog posts, my aim is to provide a useful set of notes that can be used by junior engineers as an introduction to masonry (or experienced engineers as a 'reminder'), and then to build on this basic foundational knowledge by delving into the more complex topics that arise when dealing with masonry structures, such as assessing damaged masonry, facade retention of listed structures, masonry arch bridges, propping and needling, and so on.
What is Masonry?
As basic as this sounds... there's more to it than saying that it's just a brick!
Masonry is basically an arrangement of building blocks (units) which are usually (but not always!) bonded together with mortar to form a structure. These units can be made from a wide variety of materials, from the most traditional like stone and clay bricks, through to modern options such as concrete blocks and aerated concrete. The type of masonry you come across depends heavily on the period of construction, local materials, and the intended function of the structure.
Common Types of Masonry
Brick Masonry (Clay or Concrete Bricks)
The most familiar form in the UK, particularly from the Georgian period onwards. Clay bricks remain the dominant choice, while concrete bricks are sometimes used for cost or aesthetic reasons. Brickwork can be solid, cavity, or form part of a veneer system.
Stone Masonry
One of the oldest construction methods. This ranges from ashlar masonry (finely cut stone with tight joints) to rubble masonry (rough, irregular stone, sometimes dressed on the exposed face). Stonework is durable and often found in historic or listed buildings... think of Glasgow or Liverpool City Centre.
Concrete Blockwork
Standard hollow or solid concrete blocks became widespread after WWII, when speed of construction was critical. They’re larger than bricks, making them quicker to lay, and they often form structural walls later clad in brick or other finishes.
Aerated (Lightweight) Concrete Blocks
A more recent development, these are lighter and easier to handle, with good insulation properties. They’re not as strong as dense concrete blocks, so their use is generally for partitions or infill rather than major loadbearing elements.
Composite Masonry
This is where two or more types of units are combined - for example, stone facing with brick backing, or brick outer walls tied to a concrete block inner leaf. This approach balances cost, strength, and appearance.
Cavity Walls
Since the 1920s in the UK, cavity walls (two parallel “skins” of masonry separated by an air gap) have become standard. Originally introduced to reduce moisture penetration, the cavities are often filled with insulation in modern construction to improve thermal performance.
Why This Matters
For engineers, recognising the type of masonry is just as important as spotting cracks or displacement. Each system behaves differently:
Stone walls might be incredibly durable but irregular in strength.
Brickwork is relatively uniform, but bond pattern and mortar type change how it moves under load.
Cavity and composite walls can present hidden weaknesses if the ties or connections fail.
Having this context is important as an engineer because it's going to help you make better judgements about how a wall is performing and what support or intervention it might need.
At this point, I will take the opportunity to refer you to the Brick Development Association (https://www.brick.org.uk/) which, as you might have guessed by the name, are a brilliant authority on everything to do with bricks. I would particularly recommend their guide to Eurocode 6 (Masonry Structures) which you can find here: Introduction to Eurocode 6 – Masonry Structures (BDA Guide)
Lime Mortar or Cement Mortar... or Both?
For centuries, the standard binder in masonry was lime mortar. It was relatively easy to produce (burning limestone to create quicklime, slaking it, and mixing it with sand), and it gave walls a certain flexibility and breathability that matched the materials and construction methods of the time. This changed in the 19th century, when Portland cement was patented in 1824 and gradually became more affordable and consistent in quality.
From the mid-to-late 1800s onwards, builders began mixing cement with lime to create hybrid mortars (often called “gauged mortars”). These gave the best of both worlds - cement added strength and faster set, while lime kept the mix workable and less brittle. By the early 20th century, cement mortars were becoming common in urban housing and public works. After the Second World War, the need for rapid, large-scale rebuilding meant cement largely replaced lime altogether in mainstream construction.
So, if you’re looking at a structure:
Pre-1930s; it’s very likely to be lime mortar.
1930s–1950s; you’ll often find a mix of lime and cement.
Post-war onwards; almost always cement mortar.
How to Tell Them Apart on Site
When you’re inspecting masonry, a quick check of the mortar can tell you a lot about the age and performance of the wall:
Lime mortar:
Softer and can often be scraped or powdered with a fingernail or screwdriver.
More porous - absorbs water but also dries out quickly.
Usually lighter in colour, sometimes with visible lime inclusions.
Cracks tend to be hairline, with the mortar still bonding well to the brick.
Cement mortar:
Hard and dense - difficult to scratch or crumble by hand.
Less permeable, so moisture often drives through the bricks instead of escaping through the joints.
Generally darker grey in colour.
Cracks, when they occur, can be wider and the bond to brick can fail suddenly.
Lime–cement mortar (gauged):
Often somewhere in between, moderately hard but still workable.
Slight cement-grey tint but not as dense as pure cement mortar.
For a temporary works engineer, knowing whether a wall is held together by lime or cement isn’t just a curiosity, it changes how you approach assessment, repair, and propping. Lime-based walls are more forgiving and flexible, but they don’t like being forced with rigid repairs. Cement-based walls are stronger in the short term but can be brittle, especially when exposed to weathering.
Bond Pattern
When we talk about bonding in masonry, we’re describing the pattern in which bricks are laid and how the joints are arranged to tie the wall together. A good bond spreads load evenly, increases stability, and improves appearance. Different bonds developed over time for different structural and aesthetic reasons, and recognising them can give you quick clues about a wall’s age, quality, and construction.
Stretcher Bond
Bricks are laid with their long face (stretcher) showing, with each course offset by half a brick.
Very common in modern cavity wall construction, where the outer leaf is only one brick thick.
Quick to build but not structurally strong on its own—needs ties or a backing wall.
Header Bond
Bricks are laid with their short face (header) showing, with each course offset by half a brick.
Often found in thicker walls where strength is needed, or in curved work like arches.
Strong bond but less common today because it’s material-intensive.
English Bond
Alternating courses of headers and stretchers.
Extremely strong and durable—traditionally used for loadbearing walls and still considered one of the best structural bonds.
Easy to identify on historic buildings.
Flemish Bond
Each course alternates headers and stretchers along its length, with headers centred over the stretchers below.
Popular in Georgian and Victorian housing because it’s visually attractive.
Not quite as strong as English bond, but widely used historically.
Garden Wall Bonds (Common Bonds)
Variations like English Garden Wall (one header course every three stretcher courses) or Flemish Garden Wall (one header for every three stretchers in a course).
Developed to save bricks while keeping a bonded appearance.
Frequently seen in boundary walls or less critical structures.
Stack Bond
Bricks are stacked directly one on top of the other with joints aligned vertically.
Not a true bond structurally—relies heavily on mortar strength or reinforcement.
Used for decorative facades or non-loadbearing partitions.
Why Bond Matters
For an engineer, identifying the bond type helps you understand both the era of construction and the structural behaviour of the wall:
English and Flemish bonds usually point to older, solid brickwork (pre-20th century).
Stretcher bond almost always indicates modern cavity walls.
Stack bond signals decorative or reinforced work.
This knowledge helps when deciding how a wall might perform under load, where weaknesses might develop, and what approach to take if temporary works or propping are needed.
Further Reading
As part of your on-going Continual Professional Development, and to bolster the very basics covered in this article, it is recommended that the following documents and articles are read to understand some of the key aspects of masonry:
What to Expect Next...
Articles that build on the topic of masonry, with hopefully useful notes that can be used for introductory learning, as well as crib sheets and guidance that can used to help with design or when inspecting structures and situations on sites.