Repointing Tools and Techniques: Chisels vs Angle Grinder Rake, Joint Profiles — Bucket Handle, Flush, Weathered and Recessed

Summary

Repointing is one of the most commonly requested masonry jobs and one of the most commonly done badly. The two most frequent errors are raking out too shallowly (leaving less than 20 mm of depth, which means the new mortar has insufficient key and will pop out within 1–3 winters) and using a mortar that is too strong for the brick (typically Portland cement-rich mixes used on soft Victorian or Georgian brickwork, which causes salt crystallisation damage to the brick face).

The choice between hand chisels and mechanical raking is not just a question of speed. On modern, hard engineering brick or concrete blockwork, an angle grinder with a mortar-raking disc is fast and low-risk. On Victorian or earlier soft-stock brickwork, the margin between the mortar joint and the brick arris is often as little as 2–3 mm, and a mechanical disc will cut into the brick face if the angle, pressure, or disc geometry is not perfect. Historic brickwork damaged by over-aggressive mechanical raking is irreversible.

Joint profiles also matter more than most tradespeople realise. A struck/recessed joint that would be appropriate on a sheltered internal courtyard will cause water ingress on an exposed north-facing elevation. A flush joint on Victorian stock brick will trap moisture at the brick/mortar interface and accelerate frost damage. Matching the original profile — and the original mortar mix — is the correct specification for repair work.

Key Facts

• Minimum raking-out depth — 20 mm under BS 8221-2:2000; in practice aim for 25 mm to ensure a reliable key
• Angle grinder disc types — purpose-made mortar raking discs (double-disc "turbo" cutters) are safer than standard cutting discs; never use a cutting disc for raking — it will cut into the brick
• Chisel types for repointing — plugging chisel (for striking out perpendicular joints); Dsquire or "lime-pointing" chisel for horizontal (bed) joints
• Hand raking speed — approximately 0.5–1 m² per hour for a single operative; mechanical raking 3–6 m² per hour
• Mortar strength rule — mortar must be weaker than the masonry it bedded in; hard Portland cement mortars used on soft bricks cause spalling
• Historic masonry standard — BS 8221-2:2000 (Repair of masonry); Historic England guidance "Pointing Historic Buildings" (2015)
• NHL (Natural Hydraulic Lime) — NHL 2, NHL 3.5, NHL 5 — mortar for historic and soft-brick masonry; mix depends on exposure and original mortar
• Pre-Victorian brick hardness — handmade bricks before c.1850 are typically softer than machine-made bricks; may require NHL 2 or lime putty mortar, not Portland cement
• Joint width — standard brick joint is 10 mm; tuck pointing creates 3 mm ribbon joint; any repointing must maintain the original joint width
• Wetting the substrate — dry masonry must be well-wetted before applying new mortar; dry substrate draws moisture from mortar and causes premature curing failures
• Curing — new lime mortar must be protected from frost for 7 days minimum; from direct sun and drying winds; lightly mist with water in warm weather
• Weathered joint direction — slope must always direct water away from the wall — outer face lower than inner; if sloped the wrong way it funnels water into the wall

Quick Reference Table

Detailed Guidance

Raking Out — Hand Tools vs Mechanical

Hand raking using a plugging chisel (for perps — vertical joints) and a flat cold chisel or Dsquire chisel (for bed joints — horizontal) is the preferred method for:

• Listed buildings and properties in conservation areas
• Pre-1919 brickwork of any type
• Any soft or hand-made brick where the arris is fragile
• Tuck-pointed joints where the false ribbon must not be disturbed beyond the mortar

Technique: cut into the joint at a 45° angle from each side rather than directly along the centreline — this fractures the mortar rather than levering against the brick. Use a hammer weight of 450–700 g; heavier hammers transfer too much vibration to the masonry.

Mechanical raking using an angle grinder with a double-disc mortar-raking attachment (sometimes called a "brick tuck") is acceptable for:

• Modern machine-made bricks (post-1950s) with tight, consistent joint widths
• Concrete blockwork
• Hard mortars that have been over-pointed with Portland cement

The risk with angle grinders: the double-disc width is typically 6–8 mm — narrower than most mortar joints. However, operator drift and the temptation to widen the cut by angling the grinder causes the disc to ride onto the brick edge, permanently scarring the arris. Once a brick arris is scored or chipped, it cannot be repaired without full brick replacement.

If using a mechanical rake, always:

• Check the joint width with a scribe before selecting the disc width
• Work slowly, keeping the disc central to the joint
• Never use a single cutting disc — raking discs are designed to ride the joint walls; cutting discs will cut freely and are impossible to control in mortar joints
• Wear hearing protection, eye protection, and an FFP3 dust mask — silica dust from mortar raking is a significant respiratory hazard under COSHH

Mortar Mix Selection

The single most important technical decision in repointing is the mortar mix. The fundamental rule is: mortar must be weaker than the brick.

Portland cement mortars (e.g., 1:3 OPC:sand or 1:1:6 OPC:lime:sand) are appropriate for:

• Post-1945 machine-made bricks (Class B engineering bricks and above)
• Concrete block
• Modern calcium silicate (sand-lime) brick

NHL and lime mortars are required for:

• Pre-1919 soft-stock brickwork (London Stock, Suffolk White, handmade bricks)
• Stone masonry (limestone, sandstone, Cotswold stone)
• Listed buildings — a Portland cement mix can result in enforcement action requiring removal
• Any masonry where the original mortar was lime-based

Standard NHL mixes for repointing:

Never use a bagged ready-mix "pointing mortar" on historic masonry — these products typically contain Portland cement and are far too strong for pre-1900 brickwork. Match the original mortar colour using natural sand aggregates; artificial colourants are not appropriate for conservation work.

Applying the New Mortar

Preparation:

1. Rake out to minimum 20 mm (aim for 25 mm)
2. Brush out all dust and debris — use a stiff brush and compressed air if available
3. Wet the joint thoroughly using a brush and water; allow to become "mat damp" — not wet enough to run, but not visibly dry
4. Wet again immediately before applying mortar
5. Apply mortar in layers no thicker than 10–12 mm; for deep joints, apply two layers with the first partially hardened before the second

Applying mortar:

• Use a pointing trowel (4"–6" blade) or a "frenchman" tool for profiled joints
• Pack the mortar firmly into the joint with a firm pressing motion — do not smear along the surface
• Bed joints (horizontal) first; perpendicular joints (vertical) second
• Leave slightly proud of the face by 2–3 mm initially; profile once the mortar has stiffened to "green" hardness (can be indented with a thumbnail but does not smear)

Profiling (timing):

• Bucket handle: draw the bucket handle or a 12–15 mm dowel along the joint when green-hard
• Weathered: cut the lower face with a frenchman or angled trowel when green-hard
• Flush: scrape flush with a Dsquire or pointing trowel when green-hard — do not wait until fully set

Protecting New Mortar

Lime mortars are vulnerable to:

• Frost: must not be applied or allowed to freeze within 7 days of application; cover with hessian and insulating blankets in cold weather
• Rapid drying: direct sun and drying wind causes shrinkage cracks; mist with clean water and cover with hessian for 3–5 days
• Rain: heavy rain before the mortar has set can wash the binder from the face; cover with polythene in wet weather

Portland cement mortars cure faster and are more frost-tolerant, but should still be protected from freezing within the first 24 hours.

Tuck Pointing — Specialist Technique

Tuck pointing is a specialist masonry technique historically used to give cheaper, rough-faced brickwork the appearance of precisely jointed fine brickwork. It involves:

1. Filling the full joint with a mortar coloured to match the brick face
2. Cutting a 3 mm groove along the centreline of the coloured mortar before it fully sets
3. Filling the groove with a white lime putty "ribbon" that stands slightly proud of the face

The result mimics the precise hairline joints of premium Georgian and Regency brickwork. Restoration of tuck pointing requires matching the original coloured mortar and ribbon colour exactly — specialist products are available, and the technique requires significant practice.

Tuck pointing on historic buildings in conservation areas should be carried out by a mason experienced in the technique; poor tuck pointing is worse than flush pointing because the false joints draw the eye.

Frequently Asked Questions

How do I know if the existing mortar is lime or Portland cement?

Visual clues: Portland cement mortar is typically grey, very hard, and brittle; lime mortar is buff/cream/pale, slightly softer, and can often be scratched with a penknife or scraped with a chisel without vibrating the brick. A more reliable test: drop a small amount of hydrochloric acid (diluted 10:1) on the mortar — Portland cement will react vigorously; lime putty reacts slowly; hydraulic lime reacts moderately. Do this away from the brick face and wash off immediately.

My customer wants bright white pointing on old brickwork. Should I do it?

White pointing ("ribbon" or "tape" pointing) using a wide white mortar stripe is a common request but should be discouraged on historic brickwork. It gives a very high-contrast finish that many people associate with badly repointed Victorian terraces, and it does not correspond to any historic joint profile. On a conservation area property, it may attract enforcement attention. If the customer wants a pale finish, match the original mortar colour as closely as possible using silver-grey or buff aggregates with natural hydraulic lime.

What PPE is required for repointing work?

At minimum: FFP3 dust mask (silica dust from mortar and brick is a COSHH-regulated substance), safety glasses (grinding/chipping produces sharp fragments), hearing protection (angle grinders exceed 85 dB), and knee protection for low-level work. Under the Control of Substances Hazardous to Health (COSHH) Regulations 2002, silica dust is classified as a hazardous substance — RPE must be selected from the HSE's approved RPE selector tool.

Can I repoint a wall in winter?

Hydraulic lime and Portland cement mortars can be applied in temperatures as low as 3°C provided the temperature is not expected to drop below 0°C for 7 days after application. Lime putty mortar (non-hydraulic) should not be applied below 5°C. In all cases, protect fresh pointing with hessian and bubble-wrap insulation overnight.

Regulations & Standards

• BS 8221-2:2000 — Code of practice for repair of masonry; repointing guidance

• Historic England guidance: Pointing Historic Buildings (2015) — Mortar selection and technique for pre-1919 masonry

• COSHH Regulations 2002 — Silica dust control during masonry work

• Control of Noise at Work Regulations 2005 — Angle grinder noise above 85 dB triggers assessment obligation

• Planning (Listed Buildings and Conservation Areas) Act 1990 — Listed building consent required for works altering character of listed structures; Portland cement on historic masonry may require consent

• BS EN 998-2:2016 — Masonry mortar specification

• Historic England — Pointing Historic Buildings — Technical guidance for conservation work

• HSE — Silica dust and COSHH — Respiratory hazard information

• NHBC Standards Chapter 6.1 — External masonry and mortar

• Lime Green Products — Technical Data Sheets — NHL mortar mixes and application

• Construction Industry Training Board (CITB) — Masonry training standards

• mortar mixing guide — Cement and lime mortar mixes by application

• brick types guide — Identifying brick types before specifying mortar

• damp diagnosis — Distinguishing repointing failures from other damp causes

• listed building works — Consent requirements for works on listed buildings