How to Repoint Brickwork: Mortar Mix Ratios, Tools & Joint Profiles

Summary

Repointing is one of the most common and most frequently bodged jobs in UK brickwork maintenance. The mortar joints on a brick wall are deliberately sacrificial — they're softer than the brick so that thermal movement and moisture movement crack the mortar, not the brick itself. When tradespeople repoint with a mortar that is too hard (too much cement), they reverse this principle and the bricks start to spall and crack. Getting the mix right is more important than getting the joints looking neat.

Most Victorian and Edwardian property in the UK was built with lime mortar — weak, flexible, vapour-permeable. Repointing these walls with a strong cement mortar traps moisture inside the masonry, accelerating brick erosion and causing salt staining. English Heritage and Historic England publish detailed guidance on this, and it is now well-established among conservation professionals that hard cement repointing of old brickwork causes long-term structural damage.

For post-1920s cavity wall construction, the mortar was typically a cement:lime:sand mix or a straight cement:sand. These can be repointed with a modern mix, though matching the sand type and colour is essential for an acceptable visual result.

Key Facts

• Raking depth — Old mortar must be removed to at least 15mm depth (preferably 20mm) for the new mortar to bond and have sufficient depth to weather
• Too-hard mortar — A mortar stronger than the brick will cause brick spalling and should never be used on pre-1920 brickwork
• NHL lime — Natural Hydraulic Lime is graded 2.5, 3.5, and 5. NHL 2.5 for sheltered/soft brick; NHL 3.5 for most exposed walls; NHL 5 approaching cement strength (rarely needed for repointing)
• Standard pointing mix (post-1920 brick) — 1 cement : 1 lime : 6 sand (M4 designation) or 1:4 cement:sand with plasticiser
• Victorian/Edwardian mix — 1:2.5 NHL 3.5 : sharp sand, or 1:3 for sheltered positions
• Never use OPC-only mortar on pre-1920 brickwork — this is the single most damaging thing you can do
• Sand colour — Must match existing or the repair will be obvious. Obtain a sand sample before mixing
• Cure time — Lime mortars take much longer to cure than cement — keep damp for 3 days, avoid frost for 3 weeks minimum
• Frost — Do not repoint when air temperature is below 4°C or forecast to drop below 4°C within 24 hours
• Joint profiles — Weatherstruck (sloped to shed water), flush, recessed bucket-handle, and ribbon (raised). Match existing profile
• Tooling — Tool joints when mortar is thumbprint hard (typically 30–60 minutes depending on temperature). Too early = drags mortar; too late = mortar crumbles
• Raking tools — Plugging chisel + club hammer, angle grinder with tungsten disc (use with care near soft brick), or oscillating multi-tool

Quick Reference Table

Detailed Guidance

Assessing the Existing Mortar

Before mixing anything, test the existing mortar. Scratch it with a steel nail:

• Scratches easily, powdery — original lime mortar, use NHL or lime
• Scratches with effort — moderate cement content, use 1:1:6 mix
• Hard to scratch — high cement, match with 1:4 cement:sand

Collect a sample of the old mortar and the local sand. Your builders merchant can often help match the sand. For listed buildings or conservation area work, send a mortar sample to a specialist laboratory for analysis before proceeding — this costs approximately £150–£300 but is essential for any significant heritage project.

Raking Out

This is the stage most often rushed. Insufficient raking is the number one cause of pointing failure.

By hand: Plugging chisel and 2–3lb club hammer. Chisel across the centre of the joint, then lever out. Time-consuming but safest for old or soft brick.

Angle grinder: Use a 115mm grinder with a 4mm tungsten mortar raking disc. Run the disc along the centre of the joint — NEVER along the edges where it will damage the brick arris. Keep the guard in place. Wear FFP3 dust mask (silica dust risk), safety glasses, and hearing protection. Only suitable for harder cement mortars.

Multi-tool: Oscillating multi-tool with mortar raking blade. Slower than angle grinder but much more controllable. Good for softer mortars and small areas.

Required depth: Minimum 15mm. 20mm is better. Measure with a steel ruler regularly. If you can't get 15mm depth without damaging brick, stop and reassess — the mortar may be bond with the brick face.

Cleaning and Wetting

After raking, brush out loose material with a stiff-bristle brush or compressed air. Dust and loose particles will prevent the new mortar bonding. Immediately before pointing, dampen the joints and surrounding brick faces with a misting spray bottle — not soaking wet, just dampened so the brick doesn't draw moisture out of the fresh mortar too fast. In hot weather, this is critical.

Mixing Mortar

Lime mortar (NHL): Measure by volume. Mix NHL powder with sharp sand dry first. Add water gradually — lime mixes are stiffer than cement mixes. Should hold its shape when squeezed but not slump. Do not add cement to an NHL mortar mix.

Cement:lime:sand (gauged lime mortar): Mix sand and lime first, then add cement, then water. The lime improves workability and reduces cracking.

Bagged ready-mix: Various manufacturers (Easipoint, Sika, Bostik) produce premixed repointing mortars in different colours. Convenient for small areas but more expensive per m².

Mixing machine: For larger areas, a paddle mixer gives more consistent results than a drum mixer. Mix no more than you can use in 45–60 minutes (shorter in hot weather).

Applying the Mortar

Use a pointing trowel or a narrow hawk and trowel combination. For deep joints, build up in two or three layers of no more than 10mm each — thick layers will sag and crack as they dry.

Technique: Push mortar firmly into the joint. Work from top of wall to bottom on each section. Avoid spreading mortar on the brick face — clean off immediately with a damp brush.

Sequence: Do all horizontal (bed) joints first, then vertical (perpend) joints. This gives a cleaner finish at intersections.

Tooling the Joints

Tool when mortar is thumbprint hard — press your thumb against the joint and it should leave a clear impression without mortar sticking to your thumb. If mortar sticks, wait longer; if it crumbles, you've left it too late.

Use a pointing iron, jointing tool, or purpose-made rubber jointing roller depending on the profile required.

Protection and Curing

Cover fresh pointing with damp hessian or polythene if rain is expected within 48 hours. Protect from direct sun for at least 48 hours. In cold weather (below 10°C), slow the set down with a permeable covering — lime mortars are particularly vulnerable to frost damage before carbonation has begun.

Frequently Asked Questions

Can I use a bagged dry-mix for pointing?

Yes, for small areas on post-1920 brickwork. Ready-mix products from manufacturers like Sika or Bostik are convenient and colour-matched. However, for large areas or heritage work, mixing your own gives better control. Always check the designated mortar class — a bag labelled M10 would be far too strong for most domestic repointing.

The existing pointing is still solid in places. Do I have to rake it all out?

You only need to repoint where the mortar is defective — hollow-sounding, cracked, recessed more than 10mm, or missing. Raking out sound mortar and repointing creates unnecessary disruption. However, if you are repointing for appearance reasons, you should do the whole elevation to achieve a consistent look.

How do I match the mortar colour?

Colour matching is achieved by using the same sand type and colour as the original. Cement itself is mid-grey, lime is off-white. Most brickwork uses a regional sand that gives a distinctive colour. Try to obtain sand from the nearest builders merchant first. If the existing joints are weathered, clean a section with water to see the original colour before matching. Pigment additives are available but use sparingly — they can affect mortar strength and durability.

Is repointing a conservation area house different?

In a conservation area, the materials must be appropriate to the building. Most local planning authorities (LPAs) discourage or prohibit the use of cement mortars on pre-1920 buildings. You do not generally need Listed Building Consent for like-for-like repointing (using the same materials), but you should use NHL lime mortar and match the joint profile exactly. Check with the LPA if you are unsure.

What's the lifespan of good repointing?

Well-executed repointing using an appropriate mortar on a sound brick wall should last 30–60 years. Lime mortar repointing on a Victorian wall done correctly should outlast the builder who did it. Poor repointing (wrong mix, insufficient depth, bad tooling) may start failing within 5–10 years.

Regulations & Standards

• BS 4721 — Specification for ready-mixed building mortars (mortar class references)

• BS EN 998-1 — Specification for masonry mortars (modern European standard, M1–M20 classification)

• BS EN 459 — Building lime standard (covers NHL grades)

• PD 6697:2010 — Recommendations for the design of masonry structures (contains mortar guidance)

• Historic England Practical Building Conservation — Essential reference for pre-1920 brickwork

• Approved Document A — Structure (indirectly relevant to masonry wall integrity)

• Historic England: Mortars, Plasters and Renders — Authoritative guidance on lime mortars for heritage buildings

• NHBC Technical Guidance on Masonry — Modern masonry mortar specifications

• HSE Silica Dust Guidance — PPE and LEV requirements for mortar raking

• brick matching — Matching brick type and colour for repairs

• cavity wall ties — Cavity wall tie failure and replacement

• rising damp — Inadequate DPC and pointing failure as damp pathways

• conservation areas — Conservation area material restrictions