Caring for Corfe Castle

Stonework conservation

 

Repointing is a conservation technique used to repair and replace damaged mortar. Mortar is the binding material between the stones. It plays a vital role in preventing rainwater from infiltrating the walls, where it can cause substantial damage. Over time mortar degrades and deteriorates.

It is important to use the correct type of mortar to replicate the original colour and texture so that it blends in with the rest of the masonry. Careful analysis has been undertaken to ensure the correct mix of mortar is used, retaining the authenticity of the castle’s stonework.

Corfe Castle was built using lime mortar, which has been used in construction for over 1,000 years. It is relatively permeable, allowing trapped moisture in the walls to escape. However, climate change is beginning to have an impact. Prolonged periods of drought and hot weather can dry out the mortar, causing it to become brittle and come loose.

 

Soft capping

 

The National Trust uses a technique called soft capping to protect the exposed wall tops in the ruins.

Soft capping is the use of vegetation to protect the masonry beneath. It prevents excessive rainwater and moisture from damaging the internal structure of the walls. It is ‘breathable’, allowing moisture inside the wall to escape, protecting it from freeze/thaw damage and erosion. It also helps regulate the temperature of the exposed surfaces from extreme temperatures.

This differs from techniques used prior to the National Trust’s ownership of the castle. Throughout the 1900s The Ministry of Works employed ‘hard capping’ which utilised cement to cover exposed wall tops. However cement is rigid and prone to shrinking and cracking over time, allowing water into the wall. Soft capping is a natural system so can adapt to a changing climate, continuing to protect the castle for generations to come.

 

Replacing loose stones

 

Despite our best efforts, periodically stones come loose from the castle ruin. Dedicated staff undertake regular inspections where any loose stones are recorded, carefully stored, and kept safe until specialist conservationists can put them back from where they came.

 

Vegetation removal

 

Corfe Castle has become a haven to plants and animals alike. The castle is home to many important species such as endangered lichen and Peregrine Falcons. However, there are some types of vegetation that can cause damage to the fabric of the castle.

Species such as ivy and valerian can take hold in cracks and crevices within the damaged walls, where their roots can weaken the structure. Their removal is an on-going battle, and our dedicated staff can only reach so high. Specialist contractors remove inaccessible vegetation, ensuring the underlying masonry is secure.

However not all vegetation is damaging. Ivy is very effective at protecting the underlying stone from extreme temperatures and weather. It also prevents airborne pollution from degrading the stone. We strike a careful balance between removing destructive ivy and keeping that which helps to look after the castle.

 

Plaster conservation

 

A surprising amount of plaster remains on the ruin, in some unexpected locations. It is very vulnerable to separation from the stone if water gets behind it. A technique is used whereby the plaster is fixed back to the masonry and the edges are ‘feathered’ to allow moisture to run off rather than trickle behind.

 

Harling and hearting

 

Throughout the castle the walls are made with rubble and then dressed in impressive, well-cut stone known as ashlar. When the castle was destroyed much of the ashlar was lost, walls torn apart and the internal rubble core exposed.

This rubble core is made up of small pieces of stone, bedded loosely in lime mortar, making it vulnerable to the weather when exposed. To protect it we use a technique called harling; a thrown course lime mortar finish. As with all mortar it degrades over time and needs reapplying to continue to protect the exposed core of the walls.

Hearting is the small, slim stones used to fill in the gaps between the external layer of stone in the wall. Larger hearting is used near the bottom of the wall and smaller pieces near the top. The tighter the hearting, the stronger the wall. But over time these pieces of stone can come loose, alongside with the mortar. Part of our conservation work is to re-instate this hearting where it is missing.

 

Visitor route improvements

 

We are fortunate to welcome a quarter of a million visitors a year to the castle, however this does take its toll. To help guide our visitors through the site more safely and easily we are making improvements to steps and handrails. We encourage our visitors to explore the castle ruins however for the safety of all visitors, and for the protection of the castle, please don’t climb on the ruins of the castle.

 

Thank you 

With your ongoing support, we're able to continue our vital conservation work. Thank you for helping to protect these special places.