Slate cladding system helps restore a unique Landmark Trust building.

Work has finally drawn to a close on a year-long project to re-clad with Welsh Slate a unique listed Georgian building that has now been re-purposed for the 21st Century.

The Grade II* listed Cobham Dairy, in the grounds of Cobham Hall School, the only Round Square independent boarding and day school for girls aged 11 to 18 in the UK, has been lovingly restored by building preservation charity The Landmark Trust into a holiday home available to everyone to book for breaks.

The building, which was constructed in 1796 to a design by the renowned architect James Wyatt, has been refurbished using a system which involved laying slates butt-jointed rather than overlapping each other.

James Wyatt had a vested family interest in developing the use of slate in general as his brother Benjamin was the agent for Lord Penrhyn in North Wales and from 1786 managed the Penrhyn slate quarries. And so the Wyatts began to experiment with slate cladding on walls as well as roofs, finished with a sanded oil paint to imitate stone.

At Cobham Dairy, 100m2 of large 15mm-thick slate panels up to 1,000mm by 500mm arrived on site sawn cut for installation over brickwork by specialist contractors Colman Contractors.

The slates were shaped on site to replicate blocks of stone by a team of 10 and fixed by stainless steel counter screws to all the external walls including window, arch and door reveals. These were then painted in mineral paint and sand to replicate stonework.

The original Welsh slates, a mix of Penrhyn Heather Blue and Cwt-Y-Bugail from Welsh Slate’s Ffestiniog quarry, which were riven with inward-facing dressed/bevelled edges, had been on the building since its erection. But more than 200 years later, as Cobham Dairy fell into disrepair, the paint had entirely weathered and many of the slates had fallen off because the iron fixings had rusted.

Only some on the sheltered west elevation and a few shaped fragments in the reveals around the arcade arches in the cloisters were left, evidence of the high level of craftsmanship involved in the technique. The remaining salvageable slates were carefully stored by the school, overseen by a SPAB working party which re-roofed the building in double-lapped 500mm x 250mm Penrhyn Heather Blue slates, in the 1980s.

Landmark historian Caroline Stanford said: “Landmark retrieved those salvaged tiles and it has been like a giant jigsaw puzzle to re-use as many as we could. Replacements were ordered from Welsh Slate based at Penrhyn and as in the 18th Century any colour variation did not matter as we were also reinstating the sanded paint finish. With long-term maintenance in mind we used resin plugs to conceal stainless steel fixings but the end result once again looks just as James Wyatt originally intended in 1795 for this prettiest of model dairies.”

Ornamental estate buildings were the height of architectural fashion in the 18th Century. The Dairy at Cobham Hall was conceived to represent a tiny Italianate chapel topped with a slate-cladded bell tower and with four corner pavilions. The central chamber is encased behind miniature arcades of ‘cloisters’, fronted by an open loggia facing north towards Cobham Hall. This picturesque exterior concealed living quarters for a dairymaid and a central dairy whose exceptional plasterwork and finishes make it as suited to aristocratic tea parties as to butter production.

Apart from its aesthetics, the slate cladding is believed to have also served the purpose of helping to keep the dairy cool. Inside, the plasterwork of the main vaulted chamber and other rooms is ruled out to look like stone and painted in the same sandy stone-coloured finish to complement the exterior.

Eric Colman, managing director of Colman Contractors, said: “This mid-1700 listed dairy house required total restoration. The most challenging aspect was site access which was in the middle of a large field owned by a private school.”

Landmark’s project development manager Alastair Dick-Cleland said: “Colman’s were a very conscientious contractor and were keen to produce a first-class result.”

For more information about Cobham Dairy, visit Landmark’s website:



Photos: John Miller / Landmark Trust