Warren Moor Mine: Part One – the Lime Mortar task

Eleanor Lees – Land of Iron Community Archaeology Intern

For five days back in August a group of very determined Land of Iron volunteers and staff, along with one local lime mortar expert descended on Warren Moor Mine in Little Kildale to begin conservation work on the winding engine bed. During the 144 years since the mine closure tree roots, vegetation, insects and the weather have slowly eroded the site of Warren Moor Mine which includes a winding engine bed. The stonework had very little remaining mortar, and so we took on the task to re-point in order to help protect this historic structure.

Follow this link for a 360 view of the site.

A (Very) Short History of Warren Moor Mine – the story of Warren Moor Mine starts in 1857 when the Bell Brothers of Middlesbrough surveyed the nature of the ironstone in this dale, once isolated but now connected by the new railway. Investigations on the main seam revealed that it was 5-6 ft. deep but split by a band of shale and also had low iron content; only just averaging out at 26% when other parts of the Cleveland area averaged at 30%. The Bell Brothers Ltd declined the mining lease offered by the Kildale estate (landowners) and for eight years Warren Moor remained undisturbed.

Then, despite the results of previous surveys, in 1865, under John Watson and his southern investors, work began on open drift mines into the top ‘dogger’ seam. Drift mining means digging into an edge from the side, horizontally, and is much easier and therefore cheaper than digging downwards. A year later Watson took out a 42 year lease and the ‘Warren Moor Mine’ (Company Ltd) was formed. Letters suggest that the first year of the lease resulted in profit. The ironstone extracted was calcined (roasted to remove impurities) on site and then transported by rail to the blast furnaces. Work began to sink two shafts to intercept the main seam at 220 ft., along with the construction of a steam boiler house and corresponding chimney, a winding engine and a steam powered pumping engine, all to enable deep mining. By 1868, most of the structures had been completed with the exception of the downcast shaft which had only been completed to a depth of 150 ft. but by that time the Warren Moor Mine Company Ltd were in financial trouble no doubt partly due to the poor quality of ironstone leaving the Warren Moor Mines. Kildale estate reclaimed the site and all its equipment.

Four years later in 1872, the Leven Vale Company Ltd took out a lease on the site, not put off by the previous company’s failure to make the site commercial. A row of stone cottages were built to house miners and their families, these cottages appear on historic maps labelled Leven Vale Cottages – in 1972 the cottages were demolished by volunteers from Kildale village and the stone was used in the Village Hall. Regardless of the initial investment into the site by the Leven Vale Company no progress was made with completing either the downcast shaft nor any other parts of the non working downcast mine. The company continued to use the drift mines to mine the top seam but in 1874 became insolvent just like its predecessor.

So after only nine years of operation the mines were abandoned for the next 105 years until 1979 when the archaeologist John Owen and his team excavated the site providing detailed diagrams and explanations for many of the mines remaining features (Owen’s report can be found here)…

…And then along we came!

Of course we weren’t the first group to set foot on the site since then, but being in such a remote location it sometimes feels that way. Our task in August was to conserve and protect what was left of the winding engine bed and that involved re-mortaring. We started with a day of training and demonstration at Kildale Village Hall (built with the stones from the Leven Vale Cottages). Our expert, Nigel Copesy, explained the benefits of using a hot lime mortar mix over natural hydraulic limes (NHLs) or other cementitious materials, as well as explaining the science behind the mixing process and why that resulted in better effective porosity enabling buildings to shed water quicker resulting in less damp and decay. He also showed us different ways of creating a mix and some of the more extreme reactions of slaking quick lime.

Over the next four days we undertook the actual task of re-pointing the engine bed. I think we were all surprised at the amount of mortar you could put into a joint before you would feel any resistance! We used three different types of mortar on the different areas of the engine bed in order to provide the best level of protection that we could.

The first mix that we made was used to point the sides of the stonework; it consisted of two different types of sand, brick dust, quick lime, a clay based pozzolanic additive and water. This created an exothermic reaction, where a decent amount of heat was given off but quickly cooled to useable temperatures.

The second mix is appropriately named an earth lime mortar and was used to fill the larger gaps on the top of the engine bed packed with some loose stones. To make this mix a slightly different technique was used. Using some excess soil from a previous archaeological test pit, we soaked it for a few hours before adding some quicklime to give it form. This soil contained high amounts of clay which is known to work well with quick lime. Earth mortars are more common than people realise. Many traditional buildings in the North York Moors and elsewhere have earth mortars at the core of the wall. They allow the building to breathe which can help prevent damp and create a healthy living space.

Our third and final mix was used on top of the earth lime mortar and had a very high pozzolanic value, making it more durable and less permeable. As the top of the engine bed will be most exposed to weathering, the mortar used had to almost repel any rain water. Although this type of mortar would not have been used in this location traditionally; it was thought necessary to adapt the mortar on this occasion to help protect this historic monument into the future, which is now far more exposed to the elements than it was when originally built.

The result of all five days of hard work is a winding engine bed that is infinitely more protected than it was at the beginning of the week. Conserving our industrial heritage is hugely important, especially with a site like Warren Moor which still provides a snapshot in time. The Land of Iron team would once again like to thank the amazing efforts of our volunteers, Kildale estate, and also Nigel Copsey for sharing his knowledge.