Confirm whether mortar is part of the water path
Open or cracked joints at chimneys, skews, parapets, ridges and other masonry details can admit or hold water, but the nearest mortar defect may not be the only cause. Check slate, lead, copings, flaunching, gutters and internal signs before defining a pointing-only repair.
Map the affected elevation and exposure, note when damp appears and identify where water collects or discharges. This separates failed mortar from overflowing drainage, leadwork defects, loose masonry or a covering problem and helps avoid repointing sound areas without addressing the connected roof fault.
Identify the existing mortar and masonry
Record stone or brick type, joint width and depth, surface finish, colour variation, aggregate appearance and areas of earlier cement-rich or resinous patching. Do not assume every pale or soft joint is lime, and do not infer a suitable replacement solely from the building's age.
Condition matters at both mortar and masonry. Note loose faces, saturated zones, salts, cracks, hollow or detached patches and whether failure is concentrated on exposed edges. Sampling or specialist analysis may be useful where the original binder, aggregate or later repair layers cannot be distinguished confidently.
Select a compatible mortar for the location
The mortar should be specified in relation to the masonry, exposure, joint form, required finish and existing construction. Strength is only one consideration; moisture movement, workability, curing and how the repair weathers beside the substrate also matter. There is no single lime mix for every roof detail.
Historic Environment Scotland highlights the importance of stone and mortar compatibility and the decay associated with incompatible cement mortar on many traditional buildings. Record the proposed binder, aggregate, proportions or performance basis, finish and any sample panel needed before broad application.
Prepare joints without damaging surrounding fabric
Removal should target failed or incompatible material to the agreed extent without widening joints or breaking masonry edges. Define hand tools, depth, cleaning and how dust and debris will be kept out of gutters, valleys and leadwork. Loose or unstable masonry may require separate advice before repointing proceeds.
Use a trial area when removal risk, finish or colour is uncertain. Record unexpected voids, buried flashings or earlier layers found during preparation because they may change the material choice, repair depth or interface detail. Sound historic mortar should not be removed merely to create a uniform new surface.
Plan weather, curing and protection
Lime work needs a method suited to site exposure and working conditions. The plan should address pre-wetting where specified, placing and finishing, protection from rapid drying, heavy rain, frost and disturbance, and the period over which protective measures will be checked and adjusted.
Do not promise a fixed programme without the mix, detail, access and likely conditions. Sequence mortar beside lead and slate so protection does not trap water or load vulnerable materials. Keep temporary sheeting and drainage arrangements clear of the completed water path.
Coordinate mortar with slate, lead and drainage
At roof level, mortar often meets a covering or flashing. Check whether a mortar fillet is original, whether a lead detail should carry the weathering function, how slates terminate, and whether copings or gutters shed water away from the joint. Do not use mortar to conceal a failed interface.
Agree the order of masonry stabilisation, leadwork, slate repair and pointing. A lead flashing inserted or renewed after fresh mortar may disturb it; repointing above a blocked gutter will not resolve saturation. The scope should assign each interface and provide an inspection point before it is covered.
Keep consent, samples and maintenance evidence together
A change in mortar type, colour, profile or extent can affect the appearance and fabric of a protected building. Check status and ask the planning authority about the actual proposal where consent is uncertain. Keep existing-detail photographs, sample decisions and correspondence with the repair scope.
For an assessment enquiry, provide safe photographs of the masonry and wider roof, internal damp signs, known previous patching, building status and access constraints. The next step can then resolve diagnosis or sampling needs before a mix, quantity, programme or outcome is suggested.
