The freshly built, classic limekiln at Hyllestad. In operation, June 2017.

Hyllestad is renowned for its millstone quarries; the largest stone quarry landscape from the Viking Age and Middle Ages in Northern Europe. Our museum, Millstone Park, is an outdoor museum showing the millstone landscape to the public. Garnet micaschist was the stone for millstones!

Hyllestad is situated far west in Norway. The geology features a bench of impure marble running through much of the municipality (blue on map). This is the marble, a crystalline limestone, that was used in the lime burning experiment.

This is our marble! It mainly consists of calcite, but it is impure, with occurences of mica, quartz and perhaps rhodochrosite, a manganese carbonate.

Hyllestad has old lime burning traditions: At Smilla, remains of a whole little industry operating between c. 1890 and 1950 can still be visited. The kiln worked with English coal and the lime was mainly used in agriculture. It was shipped to Bergen onwards.

Before we started building our own lime kiln, we tested the marble by burning it in an electrical kiln. The experiment was succesful!

Ruling principles for building a kiln and and burning marble: Use of local materials!

One of our more important inspirations: The traditional lime kiln at Caltgera, Brigels, Canton Grisons in the Swiss Alps. More info here.

Selja medieval monastery ruins is where Hyllestad lime will be tested in the first place. The ruins have been under conservation for several years. Geir, Torbjørn, Inger-Marie and Bjørn discuss plans!

January 2017: Building the kiln starts by draining the wet site in Millstone Park, Hyllestad…

We didn’t rely too much on construction drawings. A few sketches and height indicated… Torbjørn, Geir, Bjørn Tore and Leif seem satisfied.

Stone rubble (gneiss, handstone) for the kiln provided from a local quarry with help from the youth!

Stone ready at the building site.

Building the kiln starts – first mistake: Making a firing chamber with blocks of gneiss. We did not take into account that gneiss is very susceptible to heat and thus we later had to reconstruct the chamber.

Construction well underway! Circular dry stone masonry, c. 1 m thick, with a core of small stone and gravel. The lower part of the masonry protected by earth and gravel – a «mound». Leif, Ole, Oddvin and Torbjørn.

Three air inlets (ventilation channels) laid out below the «mound». Upon burning, it was discovered that they didn’t really work that well. Scaffolding for building arches above the opening in place.

Bjørn Tore has just built the arches above the opening to the firing chamber.

The kiln masonry finished!

April 2017: Leif and Torbjørn under the new wooden building/roof by the kiln, designed by Audun Oppedal. It rains a lot in Hyllestad, and we need a dry place when working! In front: Clay for pointing the kiln’s masonry joints has been delivered.

A lot of simple testing (burning and slaking) of the marble took place throughtout the project period!

Pointing the kiln’s internal masonry joints with coarse clay.

Last minute changes 1: We were afraid that the gneiss blocks in the firing chamber would become destroyed by the heat. Thus, we protected them using modern refractory bricks.

Last minute changes 2: The inner arch in the opening secured by a steel construction. Oddvin, Sveinung and Torbjørn with our mascot: The limeburner goat!

A temporary, protective roof put in place just above the kiln by Oddvin and Leif, to protect from rain, especially when the kiln cools down after firing.

We needed more marble to fill the kiln! From our «quarry», a couple of hundred metres from Millstone Park.

Building a marble test vault – for getting some experience prior to construction of the «real thing» within the kiln. Torbjørn is happy!

Building the marble vault defining the firing chamber. Three independent arches, reinforced with another three independent arches above. If one arch falls – the vault may still carry the load of 2,5 tons!

Per, proud builder of his first «double» marble vault!

The vault defining the firing chamber from below.

Leif on producting suitable blocks and pieces of marble for filling the kiln.

Filling til kiln with 2.5 tons (c. 1.7 cubic metres) of marble well underway. Chimeys constructed in order to secure a good draught.

The kiln is filled with marble and thermocouples for controlling temperature have been installed. Said to withstand 1200 degrees, they worked for a while during burning, but then gave up… But we also measured temperatures by an IR-probe.

Firewood! 5 cubic metres of totally dry birch wood (dried indoors for five years). Later, we understood that 5 cubic was not enough, and we had to resort to burning wood of inferior quality, with great problems…

Testing whether clay on a layer of spruce branches will work for covering the kiln. Success!

Laying out a layer of spruce branches on top of the filled kiln…

…covering with coarse clay.

FINALLY: Firing up the kiln, Saturday 3 June, at 10:45 am.

Lots of people came to see! This was also the day of the traditional «Millstone market» in Hyllestad’s Millstone Park.

Happy limeburners: Per, Chris, Terje B, Terje G, Tore and Sveinung. The wooden chimney goes up in flares, leaving the chimney hole!

Gunnar measuring temperatures with a handheld IR-probe from Amprobe (IR 750 EUR). We measured each hour at several different places in the kiln.

Burning well underway! In the beginning with the door closed.

Less smoke than we expected, but on feeding the kiln (2-3 times/hour) there was the occasional outbreak!

First night of burning. The temperature in the centre of the kiln has already reached 900 degrees.

A wonderful environment with good colleagues!

Tore feels the heat on top of the kiln!

1100 degrees in the firing chamber – and the marble vault is keeping up!

In an attempt at achieving higher temperatures in the front part of the kiln, Terje B. covered the back part with clay (to reduce draught here). But, alas, we were not able to obtain the necessary 850+ degrees over a prolonged period of time. In the back part, all is still very fine!

Bits and pieces of burnt marble tended to fall through openings in the vault. We tested them, wet-slaked them immediately! Some pieces already burnt through after a little more than 24 hours. Note the classic, beige colour! A result of impurities in the marble.

…and we made whitewash from the slaked lime, painted our kiln!

Otherwise, work, work, work. 2-3 times an hour, often more frequently. Terje B. in action.

But the kiln swallowed enormous amout of firewood! After less than 48 hours our fine load of dry birch was almost empty, and we needed to do something – fast! Sivert came to our rescue, but – unfortunately – the mixed firewod did not have the same quality as the dry birch; it was dried for two years only. We simply did not know that firewood quality played such an enourmous importance. From now on, the burning was a fight to keep up temperatures! We have learnt a lesson!

We stuck to our aim of measuring temperatures every hour! Jobjørn, Gunnar and Kjell Magnar at work.

The kiln has burnt for about 40 hours. We started to get a bit worried about the wooden roof; hot up there above the kiln… So we improvised, and all went well!

Day 3. Sveinung and Torbjørn trying to keep temperatures up! The new, inferior firewood produced a lot of coal and ash, and we had to regularly empty the kiln. Note that the heat is intense now – clothing from the local fire brigade came in handy!

After 50 hours or so, the now thoroughly burnt marble vaulting started to show signs of weakness. Some stones slipped slightly down, but rapidly found their new, temporary equlibrium. Astonishing that such a vault can withstand the high temperatures, often 1200 degrees in the firing chamber. We are happy that we built it with great care, with individual arches and in double fashion…

Same problem as ever: Fine temperatures, some 900 degrees in the central/back part of the kiln (right), but rarely exceeding 7-800 degrees in front (left), despite a nice glow in the marble…

We tried to burn slightly outside of the kiln, we protected the masonry. To no avail: With the inferior firewod and construction faults, it was not possible to raise the temperature in the front part of the kiln. But in the centre and back – all still fine.

Per working in a sea of glowing charcoal!

Big thing for the limeburners! The Norwegian public radio broadcaster came to visit us on day 4! The programme was sent on July 1, listen to it here. Per interviewed by NRK’s Jan Henrik Ihlebæk.

Gneiss blocks starting to crack just outside the fire-opening. Gneiss is not the ideal stone for building a limekiln. But it is the easiest local material available… We should, perhaps, have built the kiln with our local marble…

The limeburner goat. Our mascot! Thanks, Oddvin, for such a delightful companion through days of hard work!

The firewood problem. Oddvin managed to get hold of a cubic metre of high quality birch. It helped us through another night. Sveinung and Kjell Magnar are happy!

Yet, it is very hard work now to keep up temperature! Fourth night.

Some stones in the vault start to fall down, but, overall, the vault is keeping up. Fallen-down stone – with a fine glow – goes directly to test slaking…

Oddvin slaking a piece of the burnt marble vault. His conclusion: Fantastic, light beige colour, creamy, creamy, creamy!

Limeburners’ paradise: Millstone Park in Hyllestad! Summer nights are never really dark up north!

In the course of the burning, we test-slaked many pieces that fell down in the firing chamber. Depending on marble quality, colour of whitewash applied on the kiln varied from light grey to yellowish and beige. «Blended Hyllestad lime» has a light beige colour. Classic!

Sixth day. Time to terminate the experiment. We know from tests that the marble in the central and back part of the kiln is thoroughly burned – and also that we are unable to thoroughly burn the «front load», given poor firewood and construction faults. One arch in the vault fell down. Otherwise the vault performed perfectly!

On cooling, through the sixth night, we protected the kiln with all means available. It was raining and we wanted to secure that the temperature remained as high as possible, thus avoiding «dry slaking», reaction between the highly hygroscopic burnt lime and air humidity.

Barrels and buckets ready for packing the burnt marble – Hyllestad quicklime!

Seventh day. Eight hours in a dusty hell! Torbjørn on emptying the kiln. Manual work from above. With contstant checking of quality – done by test slaking lime in various parts of the kiln. Sorting. Well-burnt lime in one bucket, parially burnt lime in another, hardly burnt lime – thrown out of the kiln to be burnt once more later. Note security: Gloves, mask and goggles. Its a dusty, highly alkaline environment!

Per in dust, dust, dust… we have reached down to the vault on empying the kiln.

Fantastic! Even after five-six days of burning to 1200 degrees, five arches of the firing vault are still going strong! Great how stone has the ability to adjust and readjust to new equilibriums!

Raining cats & dogs! But on day seven all usable quicklime packed in air-tight barrels and buckets!

A few days later: Cleaning up the alkaline environment behind the kiln. We threw out badly burnt stone on emptying the kiln, but several well-burnt stones were also – accidentally – thrown away. Stones are getting slaked in the rainy weather!

Two weeks after the burning. The site has ben cleaned up, and all badly burnt stone packed behind the kiln, ready for another burn!

Time for analysis! Temperature diagram. It shows what we already knew: The central and back parts of the kiln (reddish, yellowish, greenish curves), had temperatures high enough for the marble to become throughly burned. The front part of the kiln (bluish curves) rarely made it above 6-700 degrees. Causes: A too large fire opening and firing with mediocre wood much of the time.

The kiln emptied. The back part (left) brown and well-burnt; the front part (right) with only soot on the walls… A good indication of what the temperature curves told us: The «front load» did not get adequately burned.

Just to make it clear: The back part of the kiln, with well-burnt lime (red circle), and the front part (blue circle), with hardly burnt lime. It was related to a main opening with arches too high and a firing chamber not well enoght protected from inflowing air. And inferior firewood, as we soon had used up our 5 cubic metres of high-quality birch.

Burning marble at Hyllestad was something of a success, despite problems with the kiln and firewood. We now have about one cubic metres of well-burnt lime for slaking. You can restore quite a lot of medieval stonework with this amount of quicklime! And our slaked lime has, definitely, the classical, beige colour sought for. A result of burning impure marble! Does our lime also have hydraulic properties? Is it fine to work? Is it durable? Time will show. An extensive period of testing will now follow.

Plans! Having worked with the kiln for half a year, there is little now to stop us from making lime-burning at Hyllestad a regular activcity.

THANKS, THANKS, THANKS!!! We had a little bit of money to build and operate the limekiln. But not more than an average monthly wages or two. Thus: Almost everything that we have reported here is a result of voluntary work! Certainly more than 2500 hours… In a small community like Hyllestad, this is just the way that we simply have to make things work…