Lime Restoration on a Stone Cottage, South Somerset

The subject property is an 18th-century stone cottage in a conservation area near Montacute, in South Somerset. Like many of its neighbours in the village and surrounding settlements, the cottage is built in Ham stone – the warm, honey-coloured limestone quarried from Ham Hill, just a few miles from where the property stands. Ham stone has been used in this part of Somerset for centuries, and the cottages, farmhouses and manor buildings of the area share a distinctive golden character that defines the local vernacular.

The cottage is a two-up, two-down period property with two reception rooms across the ground floor. The original construction would have used lime mortars throughout – bedding mortar, pointing mortar, internal plaster – most likely a hot-mixed, non-hydraulic lime, finished internally with horsehair-reinforced lime plaster on the masonry walls. This is the system the building was designed for, and the system that allowed it to manage moisture quietly and effectively for over two hundred years.

At some point in recent decades, modern materials had been introduced. The owners’ concerns brought us to the property to assess what had been done and what could be put right.

Our heritage surveyor visited the property and assessed the building. The findings were consistent with what the owners had suspected:

Internally, both ground floor reception rooms had been treated with a thick cement render directly applied to the stone, finished with a gypsum plaster skim and modern paint. In some areas where the cement had cracked or where small sections had been disturbed, fragments of the original horsehair lime plaster were still visible underneath – reinforced with horsehair from local sources, exactly as the building had been finished when constructed. The presence of this original plaster confirmed both the age of the construction and the type of lime system the building was designed to work with.

Externally, the rear elevation had been repointed in cement mortar, applied directly over the original lime pointing where it survived. The cement was harder than the soft Ham stone around it, and the joints were no longer functioning as the building’s primary route for releasing moisture. With the external pointing sealed and the internal walls finished in cement and gypsum, the wall fabric had nowhere to release the small amounts of moisture it inevitably absorbed. The result was the persistent internal damp the owners were experiencing.

The diagnosis was clear: the building’s lime system had been overlaid with modern materials that were preventing it from functioning. The remediation was equally clear – remove the cement and gypsum, reinstate lime, and let the cottage do what it was built to do.

Preparation. On day one we set up dust protection across the ground floor – plastic sheeting on doorways adjoining unaffected rooms, full floor protection in the working areas, and dust extraction equipment for the messier stages of cement removal.

Internal cement and gypsum removal. The cement render was removed by hand and with controlled mechanical assistance, taking care to avoid loosening the underlying Ham stone. The gypsum plaster was stripped back at the same time. Where original horsehair plaster was found in good condition beneath, sections were retained and protected as a record of the building’s original specification. The masonry was then brushed back, allowed to stabilise and assessed for any localised repair before the new lime plaster was applied.

Internal lime plastering. Three coats of lime, applied in sequence with appropriate cure time between each:

• Base coat one – lime putty with washed sand and locally-sourced horsehair, applied to the bare stone and worked into the joints
• Base coat two – same mix, applied once the first coat had cured sufficiently, levelling the surface
• Finish coat – lime putty with fine silica sand, applied with a steel trowel for a smooth, paint-ready surface

The work was protected during cure with appropriate ventilation control and, where required, damp hessian to slow the drying and prevent cracking.

External cement pointing removal. Across the rear elevation, the cement pointing was carefully chiselled out by hand, joint by joint. Care was taken throughout to avoid damaging the Ham stone – soft limestone is particularly vulnerable to mechanical damage during cement removal, and the work needs patience rather than power. Loose mortar was brushed clear and the joints prepared for repointing.

External lime repointing. Lime putty mortar with coarse local sand, applied joint by joint and finished to match surviving original pointing where evidence was available. Protected during cure.

Throughout. Daily clean-down at the end of each working day, regular communication with the owners on programme and what to expect, and protection of the rest of the property maintained continuously.

This project illustrates a pattern we see repeatedly across South Somerset’s heritage building stock. A traditional cottage built in Ham stone and lime, performing as designed for two centuries, then compromised within a generation by the application of modern materials that the building cannot tolerate. Cement render internally, gypsum plaster over the top, cement pointing externally – three interventions, each well-meant, that together prevent the cottage from doing what it was built to do.

The remediation is not complicated, but it is specialist work. Removing the cement carefully without damaging the Ham stone. Specifying a lime mix that matches the original – including sourcing horsehair locally for the reinforcement, as the original builders would have done. Working in lime putty rather than hydraulic lime to match the softness of the original system. Allowing the right cure times and protecting the work appropriately throughout. None of this is fast or cheap, and it can’t be rushed. But it produces a result that lasts – and a building that performs the way it was designed to.

If you own a stone cottage in South Somerset and you suspect previous work has been done with the wrong materials, you’re probably right. The good news is that almost all of it can be put right.