Choosing Bricks and Mortar for Exterior Walls

Why the Pairing Matters More Than the Brick Alone

Walk down almost any street in Britain and you can read the local geology, the railway network and a century of building practice in the walls. A red-brick terrace in Bristol, a soot-darkened London stock elevation, a pale yellow Fletton in the Midlands — they were all made from clay dug within a few miles, fired in a nearby kiln and bedded in mortar mixed on the spot. That regional logic still holds, even though bricks now arrive on a pallet from anywhere in Europe. Match the brick and the mortar to your property's age and to the weather it actually faces, and the wall will sit there quietly for a century. Get it wrong and you will be repointing inside fifteen years, or watching brick faces flake off one by one.

Start With the Age of the Property

The single most useful clue is when the wall was built, because it tells you how the whole assembly was designed to behave.

• Pre-1919: soft, hand-made or stock bricks bedded in lime mortar. These walls are flexible and breathable — they absorb rainwater and dry out again. Pointing them in a hard cement mix traps moisture inside the brick, and the brick then spalls and crumbles instead.
• 1920s to 1960s: the era of the Fletton and the first serious cavity walls. A 1:1:6 cement-lime-sand mix is typical, and a moderately absorptive brick still suits the wall.
• 1970s onwards: harder wirecut and engineering-type bricks, tighter tolerances, 1:5 or 1:6 mortars with plasticiser. Frost-rated bricks became standard in exposed locations.
• Modern extensions: match the existing brick as closely as you can, but do not assume the mortar should match. A slightly weaker mix than the adjacent Victorian wall is often the honest choice.

Choosing a Brick That Suits the Job

For most UK positions you want a brick with a frost resistance rating of F2, or at least F1 for sheltered inland walls, and a water absorption low enough to shrug off driving rain. Clay bricks are graded for this, and the supplier's data sheet will tell you. Below ground level or in a retaining wall, use a Class B engineering brick — dense, strong, and happy in permanently damp conditions. Above a damp-proof course in a normal elevation, an F2 facing brick will do.

If you are repairing or extending an older property, reclaimed bricks are usually the only way to get the colour, texture and slight irregularity that make old walls look right. Buy them from a reputable reclamation yard, order more than you need, and expect to sort out the broken ones. Avoid the temptation to mix reclaimed bricks across the whole elevation: after a few wet winters, the new bricks in a patch repair will stand out anyway. Better to blend deliberately, spreading the new stock through the wall, than to create a neat rectangle that shouts "extension".

Mortar Is Half the Wall

The golden rule of brickwork is that the mortar should always be weaker than the bricks. It is the sacrificial layer: if movement or water has to cause damage, you want it to happen in the joint, not in the brick. That is why a hard 1:3 cement mix is such a poor choice for a soft Victorian wall.

For most general work, a 1:1:6 cement:lime:sand mix gives a good balance of strength, workability and breathability. Below the damp-proof course, use sulphate-resisting cement. For historic buildings, natural hydraulic lime (NHL 3.5) or lime putty mortar is the correct answer, mixed and cured according to the manufacturer's guidance — lime needs protection from frost and from drying out too fast.

Pointing matters as much as the mix. A recessed or weatherstruck profile sheds water well, while a flush finish suited to sheltered, sheltered elevations can look too flat on an exposed coast. Never rake out old lime joints and replace them with cement, however tempting the shortcut looks.

Working With Your Local Climate

Britain is not one climate. The wet, wind-driven west — Cornwall, west Wales, the Pennines, western Scotland — is far harder on brickwork than the drier east. In those areas, insist on F2 frost-rated bricks, generous roof overhangs where you can, and a well-detailed damp-proof course. Coastal sites add airborne salt, which keeps walls damp and encourages sulphate attack, so choose bricks with low absorption and avoid soft, highly porous stock.

Sulphates in the ground or in contaminated fill are another local factor. Where they are present, sulphate-resisting cement or an engineering brick is not a luxury — it is the difference between a wall that lasts and one that crumbles at the base.

Getting It Right on Site

Before anyone lays a full course, ask for a sample panel: roughly a metre square, built in the actual bricks and mortar you intend to use, and left to dry. Mortar looks appreciably lighter once it has cured, so judge the finished colour, not the wet mix. Check the panel from the road as well as from arm's length, because that is how it will be seen every day.

Then keep an eye on the basics: gauge the courses properly, keep the bond consistent with the existing work, and protect fresh brickwork from frost and from drying too quickly in summer. Order five to ten per cent extra for cutting and waste, and keep a few spares under cover. A well-chosen brick and mortar combination is one of the few building decisions you will only have to make once.