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Ironstone – not as solid as it sounds

The name ‘ironstone’ evokes a sense of strength and stability, what with it being a combination of strong metal and natural building material. It’s almost as if all fortresses and strongholds should be created from this hybrid. However, the reality is rather different; a reality a recent client of ours knows all too well.

Ironstone includes a substantial amount of iron compound, which has either been deposited directly as ferruginous sediment or created by chemical replacement. Iron has historically been smelted from this compound. Ironstone itself is a sedimentary rock, and this accumulation of components such as sandstone with iron oxides makes for a material fraught with inherent problems when used on buildings. Examples of these buildings are the parish churches at Kirby Bellars, South Croxton in Leicestershire and, in this project recently completed by WallWalkers, a huge Church in Oxford. We were called in to perform a full-scale defrass of the building and a photographic inspection to chart it’s rate of degradation.

Iron, by nature, rusts and expands when in contact with oxygen and water. Since the whole church is constructed from ironstone, the fine iron particles are rusting and expanding, forming ‘iron veins’ – long, thin lines in the stone – where a weak point then forms due to it’s expansive force. Eventually that section of the stone breaks off with wind, water and ice weathering.

The WallWalkers team needed to install bolts to allow access across the entire church building, including it’s main hall, tower, spire and domed entrance. We looked through high-powered scopes from the ground to see any specific areas of interest needing immediate work and future repairs.

The church has a walkway surrounding the building which is used as a main through-way by the public. The fact there was so much loose ironstone was very worrying and could, in fact, have been catastrophic. We completed a full-scale defrass (‘brushing’ the surface to remove the loose stonework) and were astonished by the size and volume of stone coming off in our hands (just take a look at the pictures below!). Pieces as large as somebody’s head were crumbling away without the use of tools and when we did use small raking equipment, huge sections popped off with the slightest of force and smashed to the pavement we’d cordoned off below.

All in all, WallWalkers completed the job in five days (with big delays due to the rain), with large stone pieces filling six large rubble sacks alone. We’re glad to report that the church’s visitors can enjoy their stay, without finding a huge shadow forming around their feet as a block of ironstone whistles down from above! See the project’s images below.

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Tel: 0800 160 1142
WallWalkers Ltd
Unit 55, Easton Business Centre
Felix Road, Bristol, BS5 0HE