Bargate Stone Chimney Maintenance: A Guide for Godalming Properties

What Is Bargate Stone?

Bargate stone is a calcerous sandstone from the Bargate Beds geological layer found in the Godalming area. It was quarried locally until World War II and is a defining feature of the town's architectural character. It is harder than many sandstones but softer than granite, and its iron content gives it the warm honey colour that darkens with age.

Why Cement Mortar Damages Bargate Stone

Modern cement mortar is harder than Bargate stone itself. When used for repointing, it traps moisture inside the stone rather than allowing it to breathe. Over time, trapped moisture causes the stone to spall (flake) and crumble — irreversible damage that can only be repaired by stone replacement. We see this regularly on Godalming chimneys that have been incorrectly repointed by inexperienced contractors.

The Correct Approach: NHL Lime Mortar

Natural Hydraulic Lime (NHL) mortar is softer than the stone, allowing moisture to migrate outward naturally. It is the only appropriate pointing material for Bargate stone chimneys. We use NHL 3.5 or NHL 5 depending on the exposure level, mixed with sharp sand to match the colour of the original mortar as closely as possible.

Inspection and Maintenance Schedule

We recommend annual visual inspection of Bargate stone chimneys and professional assessment every 5 years. Repointing should be carried out before mortar erosion exposes the stone joints to rainwater penetration — typically every 20–30 years with lime mortar. A neglected Bargate stone chimney can require partial reconstruction, which is significantly more expensive.

Identifying Bargate Stone on Your Property

Bargate stone is distinctive: a warm honey-brown colour with visible sandy texture and occasional ironstone nodules. It darkens with age and weathering, and old Bargate stone can appear almost brown-black on exposed surfaces. It is found on properties across the Charterhouse area (where Charterhouse School is the most prominent example), on Frith Hill, and in scattered examples through the town centre and Busbridge.

Not every stone chimney in Godalming is Bargate. Some Victorian properties used Bath stone, Portland stone, or brick with stone dressings. The correct identification matters because each stone type requires different mortar specifications. If you are unsure, we can identify the stone type during a free survey and advise on the appropriate maintenance approach.

Signs Your Bargate Stone Chimney Needs Attention

Look for: mortar that crumbles when prodded with a finger or screwdriver; visible gaps where mortar has fallen away from joints; dark staining on the stone surface below joints (indicating water is running through rather than off the chimney); any cement patches that are harder and darker than the surrounding lime mortar — these are previous incorrect repairs that need removing before they cause stone damage.

Inside your home, check the walls adjacent to the chimney stack for damp patches, especially after heavy rain. A chimney with failed pointing acts as a funnel, channelling rainwater into the masonry and through to the interior. In the Wey Valley's high-rainfall climate, this can deliver significant volumes of water into the building fabric over a single winter.

Cost of Bargate Stone Chimney Repairs

Lime mortar repointing costs 20-30% more than cement repointing due to the skill and time required. A typical Godalming chimney stack repoint costs £300-600 in lime mortar compared to £200-400 in cement — but the cement option will damage the stone and cost far more to rectify in 5-10 years. Where previous cement pointing has already caused spalling, the damaged stone must be cut out and replaced with matching Bargate stone or sympathetic repair mortar, adding £200-500 to the project depending on the extent of damage.

What Sets Our Approach Apart

Every piece of roofing work we undertake in the Godalming area follows the same core principles: survey before quoting, specify materials in writing, fix the cause not the symptom, and guarantee the result. These sound obvious but they are routinely ignored by contractors focused on volume rather than quality. We limit the number of jobs we take on specifically so that every property gets the time and attention it needs. A rushed roof repair is a failed roof repair — and in the Wey Valley's demanding climate, cutting corners leads to callbacks faster than anywhere else.

Our team includes specialists in every discipline relevant to bargate stone chimney maintenance: tile matching across every era of Godalming housing, lead dressing to Lead Sheet Association standards, lime mortar formulation for Bargate stone and other period masonry, flat roof membrane systems from both GRP and EPDM manufacturers, and mechanical ridge and hip systems for exposed locations. This breadth of in-house expertise means we handle every aspect of your job ourselves — no subcontractors, no passed-on responsibility, no conflicting guarantees.

Your Property Is an Investment — Protect It Properly

The average Godalming property is worth significantly more than the national average. A properly maintained roof protects that value. A neglected roof devalues it. Buyers and their surveyors notice roof condition immediately — it is one of the first things visible from the street and one of the most expensive items on a building survey. Whether you are planning to stay in your home for decades or considering selling within a few years, keeping the roof in excellent condition is one of the highest-return investments you can make in the property.

We offer free, no-obligation roof surveys that give you a clear picture of your roof's condition and remaining lifespan. Many of our customers use these surveys as part of their ongoing property maintenance planning — booking the work they need over a sensible timescale rather than waiting for an emergency. Call 01483 346 855 to book your survey. We typically attend within one week of your call and provide a written report within 24 hours of the inspection.