Burning Limestone In Scotland

After our very blustery and wet visit to the Scotland Working Party on the Isle Lismore, we were treated to four days of the finest Scottish summer. We had left Lismore inspired by our week of burning limestone in homemade kilns of concrete block and mud, and set off to the Isle of Mull. Logic would state it would be a quick ferry journey as we could see Mull in the distance, but logic did not ensue and we had to travel back to Oban on the mainland and catch a later ferry, Although the ferry gods were on our side as we managed to sneak onto an earlier boat and set across the sea to the wonderful island.

Greeted by beautiful clear skies with the sun setting over the mountains the weather could not have been more of a contrast to our previous week!! We were lucky to be staying at Duart Castle, a 13th century family home of the Mclean’s, a clan of Scotsmen famed for their fighting prowess and heraldry. The castle sits on a headland jutting out into the ocean surrounded by water on three sides with 360 degree mountain views, a view which has to be one of the best I have seen to date.

Inspired by our previous lime burns, we spoke with Andy Bradly our host who heard rumour of some illusive limestone on the Isle of Mull. Unlike Lismore, an island of predominantly limestone, there was not much to be found on Mull to date. Rising to the challenge we set out in the car to find some limestone, a new road widening scheme had uncovered some light stone which fitted the bill, armed with a bottle of vinegar we set off to see if we could get a fizz of calcium carbonate. Unfortunately the fizz eluded us and we returned to camp slightly disappointed. The Mull limestone was not going to give itself up that easy!!

Day two and determined not to be defeated by the limestone quandary, I accessed the university library to get the geology maps for the island. It showed two very small seams of limestone outcrops, we were off in the car again, acid in hand and determined to succeed. Stop one we got a fizz! it was lucking good but it turned out to be an anomaly, stop two again nothing, stop three and again the fizz was not to be seen. Running out of time and a tour of the castle looming we had to get back to camp and give up.

I really did not want to be defeated by this, I know the university maps showed limestone on the island surely there should be something! I corralled Dan into the car one last time and we were off, to the furthest reach on the map, an outcrop reaching into the sea. We followed a road, which got narrower and narrower and eventually ended in the middle of know were. On the side of the road we found some remnants of white stone and the excitement when we got the fizz and the immediate disappointment when we realised that it was an old bag of hydrated a lime.

We set off on foot over the cattle grid through the marsh land, fighting our way through long ferns hoping not to get pick up any ticks from the undergrowth. We came across our first obstacle a narrow steam and bog, this was tackled with much modesty and we thundered on through the undergrowth. Again another successful stream crossing and we came to a ravine, it was right where x marked the spot for the lime but it was steep and being in the middle of nowhere I had to do a quick risk assessment as there were no ambulances and we would have to call international rescue if someone rolled an ankle. Dan took the lead and shuffled down the face first, once he was safe I made my way down, we got out the acid, sprayed it on the rocks and it fizzed in a way which made me reminisce of sherbet dib dabs. We found it! The illusive limestone of Mull!

We pulled out the hammer and broke off some chunks of the seam and loaded up the plastic bucket. I think were a little exuberant in our pickings given the challenge of getting back to the car! We must have loaded up with 25kgs of stone and a handle each we scrambled our way back up the ravine, we crossed the first river and it was time to tackle the second crossing ang the bog. Just as Dan was about to place his foot and jump across, I heard a scream like a banshee, I looked down expecting him to have broken a leg, it was just fine, the earth had opened up and tried to consume Dan, he had sunk in the bog up to his thigh. Miraculously he managed to get his leg out with his shoe intact and we made the last few hundred meters back to the car unscathed. A quick high five and collapse on the bank in hot sun we took on water and made our way back to camp with happy faces and feeling like heroes with our 20 Kgs of Mulls finest limestone.

Back at camp we assessed the stone which appeared a very crystalline and slightly metamorphic limestone and planned to burn it in the morning to see if we could make quick lime.

An early start in the morning and we built a lime kiln out of a scrap BBQ grill and several concrete blocks. The blocks were not even bed, but a small amount of sand was used to seal up the beds and perp ends as best we could to retain the heat. We charged the kiln with our limestone and BBQ charcoal and we lit a fire underneath. Two thermocouples were used to monitor the temperature and once up to around 900 degrees Celsius we closed the bottom of the kiln and allowed it to burn out. Now the wait to see if we were successful in burning local lime, something which has not been (to the best of our knowledge) documented on the isle of Mull.

The Sun was low at it was time to view our spoils. We raked out the kiln to discover the limestone had tuned a salmon pink colour and roughly halved its weight. A splash of water added to the stones and they fizzled up and started to crack open and slake. We had did it, we had successfully created quick lime and it mixed up into the most beautiful consistency of whipping cream. We took a small batch and hot mixed it into a mortar to create a sample which was duly sent off for analysis. Which we are excited to discover the results, which will be very interesting to compare to the historic mortars in the castle.

The whole mini adventure for us highlighted the fact that everything came from within a stones throw from where you were working. How the material determined the vernacular, the construction techniques and style. It makes you reassess the process of shipping lime in from France or further afield when it may be available at the end of the street. Now, it is understanding that we cant all slake limes in our back gardens on the grounds of practicality and safety, but it makes reassess the footprint of materials and how, through careful choices and material selection we can repair or build buildings which are not only in keeping with the historic technique, but sustainable and protecting of the environment.”