Good lead work in Thetford is not just about putting new metal over an old joint - every stage of the process, from the initial inspection to the final clear-up, affects whether the repair lasts.
Lead flashing and valley work fails for two reasons: the wrong material was used, or the installation was done incorrectly. Of the two, poor installation is far more common. Rushed preparation, joints pointed with the wrong mortar, lead cut too long without expansion provision - these are the faults that cause callbacks and repeat leaks.
Below is a plain account of how a professional lead work job should proceed, from the first look at the roof through to leaving the site clean. Knowing the process helps you judge the quality of work being done on your property.
Before any materials are ordered or work agreed, the existing lead detail needs to be inspected properly. That means someone physically on the roof, not just looking up from the ladder. A good inspection of a chimney stack covers all four sides: the front apron, both side step flashings and soakers, and the back gutter. On a valley, the whole run is checked from top to bottom.
The inspection establishes whether the existing lead can be reused or needs full replacement, whether the mortar joints holding the flashing are sound, whether there is any underlying damage to the roof timbers, battens or felt beneath the area that has been leaking, and whether any adjacent tiles or slates need to be removed temporarily to carry out the lead work properly.
A proper inspection also checks the code of the existing lead. If the previous roofer used code 3 in a position that demands code 5, replacing like for like is not the right answer.
Unless a section of flashing is genuinely in good condition and only needs re-pointing at the top edge, old lead should be stripped out rather than worked over. Leaving failed lead in place and applying new material on top creates double layers that trap moisture, hide the true condition of the surface beneath, and make future repairs harder.
Stripping out a chimney flashing means removing the pointing mortar from the chase, taking out each piece of flashing, and cleaning the masonry surface. On a valley, the tiles either side of the valley are carefully removed and stacked so they can be relaid afterwards. The old valley lining - whether lead, mineral felt or code-light lead - comes out completely.
Any tiles or slates that are cracked or broken during stripping are replaced as part of the job, not left for later.
With the old lead removed, the substrate is checked before new material goes in. On a chimney stack, this means looking at the condition of the brickwork and mortar joints. Spalling bricks or open joints need to be made good before the new flashing is fitted - you cannot seal a flashing into crumbling mortar and expect it to stay put.
On a valley, the roofing felt or breathable membrane in the valley area is inspected for splits or holes. If the felt has deteriorated, it should be replaced before the new valley lining goes in, because the felt is the secondary defence if water ever gets past the lead. The valley boards or rafter surface beneath are checked for rot, particularly if there has been a long-running leak in that area.
Lead sheet for flashing work is supplied in rolls, coiled and cut to the lengths needed for each section of the job. The correct code (thickness) is selected for each application: code 4 or 5 for chimney back gutters, code 3 or 4 for step flashings and soakers, code 5 or above for valley linings and flat roof details.
Lengths are kept within the maximum recommended for each code to allow for thermal movement. For step flashings at a chimney side, individual pieces are cut to follow each course of masonry - typically around 150 mm steps. For a back gutter, the lead is cut and bent to form the gutter profile with an upstand at the back and a drip at the front over the tiles.
Forming the lead is done with a dresser and a bossing mallet. The lead is worked - bossed - around corners and into complex profiles without cutting the sheet where cuts would create weak points. An internal corner on a chimney base, for example, is bossed rather than cut and overlapped, because a cut corner is a potential leak point.
The top edge of each flashing section is tucked into a mortar joint that has been raked out to a depth of at least 25 mm. Lead clips or wedges are used to hold the flashing in the chase before it is pointed back in. The pointing mortar used matters: a mix that is too strong (too much Portland cement) will crack away from the lead as it moves seasonally. A 1:3 ratio mix (one part cement, three parts sharp sand), or a proprietary flashing mortar, gives enough flexibility.
Soakers on a slate or plain tile roof are slid under each course of tiles at the abutment, one per course, so that each soaker overlaps the one below. They do not need pointing - they rely on lapping and the weight of the tiles to stay in place. The cover flashing then goes over the top of the soakers and into the wall chase, creating a double line of defence at the joint.
Valley linings are dressed into the valley profile, with a splash check (a small fold at the centre of the valley) formed to prevent water crossing from one slope to the other in heavy rain. Tiles are cut to the correct angle at the valley edge before being relaid.
Any tiles or slates removed during stripping are relaid in the correct bond pattern. Broken tiles are replaced with matching material where possible - on older plain tile roofs, second-hand tiles of the same profile are sourced if new tiles would stand out. Ridge tiles or hip tiles disturbed during access are re-bedded or re-torched as needed.
Once all tiles are back in place, the lead work is checked again from the roof surface. Flashings are checked to confirm they sit flat against the wall face, that no gaps exist at the mortar joint, and that the lead is not under tension (which would cause it to pull out over time).
Tile debris, old mortar and any packaging are cleared from the roof surface and gutters before coming down. Gutters below the work area are checked to make sure no debris has entered that could block the flow. Any mortar splashed onto tile faces during pointing is removed once it has set enough to brush off cleanly.
A final check from ground level confirms the flashing sits correctly and that no tiles have been left displaced. If the customer is at home, we walk them through what was done and why - particularly if any additional issues were found during the inspection that were not part of the original scope.
If you have a chimney, dormer, lean-to roof or valley that you suspect is leaking, or if lead work was flagged on a survey report, call Brandon Roofers. We cover Thetford and nearby areas from our base in Brandon.
No obligation · We usually respond within 2 hours
Storm damage, active leak, damaged ridge - we aim to be on-site within 24 hours.
