Castle combats crumbling mortar with lime spray: Oliver Gillie watches volunteers trying out a new conservation skill on their local heritage
Thursday 19 August 1993
The man who devised it, Gordon Pearson, is an expert on earth walls and ancient forms of mortar. As surveyor of historic buildings for Hampshire County Council he is responsible for making Odiham Castle safe - a difficult job when flints the size of two fists may fall at any moment from the ruined battlements. 'In the past, the county council tried to make it safe by raking out the soft lime mortar and repointing with cement,' Mr Pearson said. 'But now we are experimenting to see if more of the original can be conserved by hardening the mortar.'
The method of spraying with lime water has been used in the past to harden limestone and lime plaster but not, so far as Mr Pearson knows, to harden mortar.
The present surface of the castle, built in 1214, was never meant to be exposed to the weather. The castle had an exterior wall of dressed limestone and was lined within with the same stone. Between these curtain walls was dumped an aggregate of flints in lime mortar. Later the curtain walls were taken away exposing the aggregate.
The castle was built for King John, who used it as a resting place when travelling between Windsor and Winchester. He stayed there overnight before going to Runnymede to meet the barons and sign the Magna Charta. In 1265 the castle came into the ownership of Simon de Montfort and his wife Eleanor - at that time the most influential family in England.
But, by 1603 it had become a ruin. Local people helped themselves to the stone, which was used to build houses in Odiham.
The lime-water treatment is being undertaken by volunteers from the Odiham Society, which is concerned with local history. Two areas of flint and mortar are being sprayed twice a day for three or four weeks. The lime water (calcium hydroxide) penetrates the mortar where it reacts with carbon dioxide from the air. As a result, calcium carbonate is precipitated within the mortar, hardening it and turning it into a denser form of limestone.
'Ideas of conservation have changed,' Mr Pearson said. 'The lime-water treatment makes use of the chemistry of the mortar itself and strengthens the whole structure. The next stage will be to get contractors to put up scaffolding and spray the whole structure.'
- 1 Nigel Farage: Me vs Russell Brand on Question Time – he's got the chest hair but where are his ideas?
- 2 Harry Potter fans can apply to the Hogwarts-inspired College of Wizardry
- 3 Jessica Chambers: 19-year-old woman 'doused with lighter fluid and burned alive' in the US
- 4 Russell Brand calls Nigel Farage 'poundshop Enoch Powell' in BBC Question Time debate
- 5 Orange Wednesdays are no more
Weather bomb in pictures: Storms cuts power for tens of thousands – and snow is on the way
Jessica Chambers: 19-year-old woman 'doused with lighter fluid and burned alive' in the US
Russell Brand calls Nigel Farage 'poundshop Enoch Powell' in BBC Question Time debate
Russell Brand was rendered speechless on Question Time by this man
Fury at Airbus after it hints the super-jumbo may be mothballed
Disgruntled RBS worker writes hilarious open letter to Russell Brand after anti-capitalist publicity stunt leaves him hungry
Nigel Farage defends Kerry Smith 'ch***y' comment: 'If you are going for a Chinese, what do you say you’re going for?'
Nigel Farage's approval rating hits 'record low' as popularity suffers in wake of Ukip sex scandal
Pakistan school attack live: Taliban kill at least 132 children in 'horrifying' massacre
Sony hack: Angelina Jolie branded 'seriously out of her mind' in further embarrassing leaked email saga
Panic Saturday: 13 million Britons spend £1.2bn – while 13 million others across the country live in poverty unable to afford food
£7 - £9 per hour: Recruitment Genius: Are you outgoing? Do you want to work in...
£30000 - £35000 per annum: Recruitment Genius: An opportunity has arisen for a...
£30000 - £35000 per annum: Recruitment Genius: An exciting opportunity to join...
£30000 - £35000 per annum: Recruitment Genius: We have an excellent role for a...