Stripping All Existing Lead and Tile Work

All existing lead flashings, soaker plates and the back gutter were stripped back to bare brickwork. The courses of plain clay tiles abutting the chimney on both sides were lifted and stored for re-use. Stripping everything back to a clean substrate is non-negotiable — there is no value in dressing new lead over failed lead, and attempting to do so inevitably produces a second failure within a few years. The old Portland cement haunching around the chimney pots was carefully chiselled away without disturbing the pots themselves.

Brickwork Repair and Lime Repointing

The six frost-damaged bricks were cut out and replaced with reclaimed matching Victorian stock bricks, bonded and pointed to match the surrounding courses. All existing Portland cement mortar joints across the stack were raked out to a minimum depth of 20mm using an angle grinder with a 1mm slitting disc — a slow, precise operation that avoids the mechanical damage that disk-cutting can inflict on the arrises of Victorian bricks.

Repointing was carried out using a 1:2.5 mix of NHL 3.5 natural hydraulic lime mortar and sharp sand. NHL 3.5 is the correct specification for exposed chimney stacks on Victorian brickwork: it is substantially softer and more flexible than Portland cement, matches the original mortar in permeability, and allows the brickwork to breathe and shed moisture rather than trapping it. The mortar was applied in two passes — a scratch coat to consolidate the joint, followed by a finish coat raked to a slightly recessed profile to shed water away from the face. All joints were protected from rapid drying during the first 48 hours using hessian sheeting. All masonry repair work was carried out in compliance with Building Regulations Approved Document A (Structure) and Approved Document C (Resistance to Contaminants and Moisture), ensuring the structural integrity of the stack and permanent resistance to water penetration were fully restored.

Code-6 Back Gutter Installation

The back gutter was the most technically demanding element of this chimney stack restoration. The gutter was fabricated on-site from code-6 milled lead sheet (BS EN 12588 certified, 2.65mm nominal thickness) in full compliance with BS 6915:2016 — the British Standard Code of Practice for the design and construction of fully supported lead sheet roof and wall coverings. Code-6 is specified for back gutters rather than the lighter code-5 used elsewhere because back gutters collect and hold standing water — a heavier gauge is essential for long-term durability. The gutter was formed in a single continuous piece where possible, with any necessary bossed joints executed using lead bossing mallets and a dresser — not soldering, which is inappropriate for this application as it cannot accommodate the same degree of thermal movement. The gutter was laid to a minimum 1:60 fall towards a lead-lined outlet on each side of the stack, and the upstand at the rear face was dressed into a freshly cut chase in the brickwork to a minimum 25mm depth, then pointed with a flexible mortar to allow movement.

Code-5 Step Flashings and Lead Soakers

New individual lead soaker plates were cut and dressed to each course of plain clay tile on both sides of the chimney stack. Each soaker is cut to an L-profile: the horizontal leg sits beneath the tile and overlaps the tile below by a minimum of 100mm, while the vertical leg turns up 75mm against the chimney face. Soakers form the primary waterproofing layer and must be sized precisely to the tile gauge — a detail that is frequently cut short by less experienced roofers.

Over the soakers, code-5 step cover flashings were dressed and fixed at each brick course. Each step flashing was individually cut to a minimum length of 200mm with a 25mm turn-in tucked and wedged into the mortar joint, then pointed over with a mortar that is coloured to match the existing stack. The critical detail — which is where most chimney flashings fail — is that the turn-in is wedged using lead wedges, not simply pressed in. This prevents the flashing lifting under wind pressure and ensures the watertight overlap is maintained under all weather conditions. All tiling and flashings were executed in compliance with BS 5534:2014 (Code of Practice for Slating and Tiling) and Building Regulations Approved Document C, meeting the required standards for weather resistance and moisture protection on pitched roofs in the UK.

Front Apron Flashing

The front apron flashing — the single lead sheet covering the junction between the front face of the chimney and the roof tiles below — was replaced in code-5 lead. The apron was cut to cover the full width of the chimney face plus 150mm each side, was dressed to follow the roof slope precisely, and the top edge was dressed into a continuous chase cut in the mortar joint with the turn-in secured by lead wedges at 300mm centres. The bottom edge was dressed over the top surface of the last course of plain tiles, with a 50mm minimum overhang. No sealant was used at any junction point — sealant-based approaches to chimney flashings are a short-term fix that invariably fail within a few years and are not consistent with Master Roofer standards.

Chimney Pot Re-Bedding and Haunching

Both chimney pots were removed, the old haunching completely removed, and the pot seating cleaned back to sound brickwork. Each pot was re-bedded in a mortar bed of NHL 3.5 lime and sharp sand. The haunching — the angled weathering collar formed around the base of the pot where it meets the top course of the stack — was built up in two passes to achieve a clean, steeply angled profile that sheds water away from the pot base at every angle. The haunch was finished with a rounded profile using a piece of lead sheet as a template to ensure a consistent, smooth weathering surface. Both pots were checked plumb in both planes before the mortar had set.