Recently, we had the challenge of sourcing handmade bricks for a project in a Conservation Area in West Lancashire. The original bricks told a story; they were likely made by itinerant brickmakers around 1860 and would have been produced in a brick clamp; a traditional method where bricks were fired in a temporary kiln built on-site. Interestingly, just across the road from the building is an old fishing pond, which was likely the original clay pit that provided the raw material for these bricks.
The handmade bricks from the original building were 80mm in height meaning this particular group of craftsmen used 80mm (3 1/8 inch) moulds, an uncommon characteristic which made obtaining a matching brick something of a protracted challenge. In the end, the search led us to the largest architectural reclamation yard in the Northwest ran by Cheshire Demolition in Macclesfield. If you’ve never been, I highly recommend visiting: it's a treasure trove of reclaimed materials.
One of the most interesting discoveries was that the bricks we found in Macclesfield actually originated from the same village in which this project is located. While we can't say for certain, it’s possible the bricks we found were originally made by the same itinerant brickmakers who made the bricks for the original building using their distinctive 80mm moulds around 160 years ago.
How to Select Reclaimed Bricks to Match Your Building
1. Matching the Size
The first factor is getting the correct size. Historic bricks often often do not conform to modern metric dimensions (i.e. bricks that are 65 mm in height). Bricklayers cannot properly course bricks of differing heights.
2. Handmade or Machine-Made Bricks?
Determine whether your bricks are handmade or machine-made. Handmade bricks are easy to identify due to their irregular shapes and distinctive creases on the sides, sometimes referred to as “smiles.” These marks were created when the brickmaker pushed the clay ‘loaf’ into the mould by hand. In contrast, machine-made bricks have a sharper, more uniform edges. Mixing machine-made and handmade bricks is not a good idea aesthetically.
3. Colour Matching
The colour of bricks is largely influenced by the clay they were made from, which was typically sourced locally in the case of handmade bricks. The natural composition of the clay and the sand used to line the moulds has a large effect on the final colour of the bricks: Pure clay is white, but other materials within the clay give it distinct shades. Iron oxide creates the classic reddish-orange hues and magnesium contributes to a bluish-yellow colour depending on how it was fired.
The firing method also plays a crucial role in colour variation. In the case of these handmade bricks, they were fired in a brick clamp; a traditional method where bricks are stacked with fuel and fired in a temporary kiln. This leads to a wide range of colour tones. The bricks closest to the fire turn a dark, almost blackened colour due to higher temperatures. The bricks further from the fire remain a softer orange. Some bricks at the outer edges of the clamp may not be fully fired and therefore not achieve vitrification, making them unsuitable for external use. In some cases these softer bricks were re-fired or used as internal bricks.
4. Ensuring Bricks Are Fit for Purpose
It’s important to select facing bricks that are suitable for external use. In the case of this building, under-fired bricks (typically lighter orange and softer) were used internally or even for footings. Using soft bricks on the external façade would result in them spalling and breaking down to to frost damage and other factors.
Choosing the Right Mortar for Handmade Bricks
Once we had sourced the bricks, the next step was specifying the correct mortar. A modern sand-cement mortar would have been unsuitable for these soft, handmade bricks even with the additional of hydrated lime.
It’s a common issue in older buildings when soft bricks are repointed with hard cement mortar, that the moisture becomes trapped within the brick rather than being able to pass through the mortar joints as it would with lime. Over time, this can cause blown brick faces, leading to significant damage. To avoid this, it was essential to select the correct lime mortar, as it is inherently more breathable and flexible. In essence; the mortar must be softer than the bricks.
Photographs showing the results of handmade bricks that were originally pointed with lime mortar being repointed with a cement & hydrated lime mortar. The cement traps moisture which eventually blows the faces off the bricks due to frost action.
A Quick Guide to Different Mortars and Their Applications
Here’s a brief overview of different mortar types and where they are most suitable:
| Mortar Type | Set Time | Characteristics | Suitable Materials |
|---|---|---|---|
|
Lime Mortar |
Very slow |
Softer mortar, ideal for conservation work and low-strength applications. | Brick (soft), Limestone (soft), Sandstone (soft) |
| Hydraulic Lime NHL 2 |
Slow |
Softer mortar, ideal for conservation work and low-strength applications. | Brick (soft), Limestone (soft), Sandstone (soft) |
| Hydraulic Lime NHL 3.5 |
Medium |
Moderate strength, suitable for general masonry and rendering. | Brick (London Stock, Fletton, Facing, Common), Limestone (Soft), Sandstone. |
| Hydraulic Lime NHL 5 |
Faster |
Higher strength, used for exposed or load-bearing masonry. | Granite, Slate, Limestone, Sandstone (Hard), Brick (Engineering) |
| Cement & Hydrated Lime (1:2:9) |
Fast |
Slower setting than pure cement mortar, improved flexibility and breathability, commonly used in traditional masonry. | Modern building materials. |
| Standard Cement |
Fast |
High early strength, commonly used for modern construction. | Modern building materials. |
For this project, a Natural Hydraulic Lime (NHL 3.5) mortar was the best choice as it was strong enough for external use but still breathable and flexible and permeable enough to work with the soft bricks.
If you are planning to alter or extend a historic building, it’s always worth seeking the guidance of a Conservation Architect in order to get the specification right. Getting it wrong can lead to significant long-term damage, while choosing correctly helps to preserve the fabric of the building for generations to come.