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Pointing, Repointing and Mortar: How to Calculate Materials
Repointing brickwork is one of the most impactful maintenance jobs you can do — but calculating how much mortar you need for pointing or repointing varies greatly with joint depth and condition.
Repointing fails or wastes money when the mortar mix is wrong or the quantities are underestimated. Here's the complete guide to getting both right.
How Much Mortar for Pointing
Joint dimensions for standard UK brickwork:
Width: 10mm
Depth for repointing: 15-20mm (old mortar raked out)
Volume of mortar per joint:
= width x depth x joint length
= 0.010 x 0.018 x length
Joints per m2 of brickwork (stretcher bond):
Horizontal beds: 14 joints (one every 75mm height)
Vertical perpends: ~4-5 per course x 14 = ~60 joints
Each perpend is ~100mm long
Total joint length per m2: (14 x 1,000mm) + (60 x 100mm) = 20,000mm = 20m
Mortar volume per m2:
= 0.010 x 0.018 x 20 = 0.0036 m3 = 3.6 litres per m2
Mortar Quantities for Repointing 10m2
Volume: 10 x 3.6 = 36 litres = 0.036 m3
Mix ratio for repointing (1:4 cement:sand by volume):
Total parts: 5
Cement: 0.036 / 5 = 0.0072 m3 ≈ 11 kg (approx 1/4 of 50kg bag)
Sand: 0.036 x 4/5 = 0.029 m3 ≈ 45 kg (half a large bag)
Add 20% waste (mortar that falls out or dries before use)
Practical order: 1 x 25kg cement bag + 1 x 25kg bag sharp sand
(this gives excess — better than running short mid-job)
Choosing the Right Mortar Mix
Location / ConditionRecommended Mix (Cement:Lime:Sand)Notes
Normal weathering, hard brick1:1:6Good balance of strength and flexibility
Exposed / severe weathering1:0.5:4.5Stronger, less permeable
Soft / old brick (pre-1920)1:2.5:10 (NHL)Must use lime mortar — cement damages soft brick
Internal walls1:2:9Weaker mix fine — no weathering
Critical rule: Never use a harder mortar than the brick. If the brick is softer than the mortar, moisture cannot escape through the mortar (which acts as a barrier) and instead freezes and expands inside the brick — causing spalling. Old soft bricks must always use lime mortar.
Raking Out Depth
Minimum rake depth: 15mm (for good mechanical key)
Ideal rake depth: 20-25mm
Less than 15mm = repointing will fail quickly
More than 25mm = weakens the wall
Use an angle grinder with a disc only for hard mortars —
for soft/lime mortars, always use hand tools (a plugging chisel)
to avoid damaging the brick faces.