Abstract

Protecting stone buildings from weathering and decay is a major challenge in the conservation of built heritage. Most of the stone consolidants currently available are well suited to silicate stones, but are less compatible with limestone. In this paper we present for the first time the results over a 4-year period of various consolidation treatments carried out using nanolime on 6 of the most representative and significant stones used in historic buildings in the United Kingdom. Tests investigated the influence of stone type, environmental conditions and pre-treatments on the effectiveness of the consolidation treatment. A comprehensive and rigorous testing programme was carried out to evaluate the short (12 weeks) and longer-term (4 years) effects. Stone samples were characterised before and after treatment using light and electron microscopy, sorptivity tests and a novel methodology employing drilling resistance to interrogate the near surface effects. Results show that for some of the stones, such as Clunch and Bath Stone, the positive effect of the treatment with nanolime is noticeable after 4 years since application. However, results for other stones such as Portland and magnesian limestone showed that the initial beneficial effect of the treatment is reduced after 4 years. Nanolime treatment of Ham Stone produced an unnoticeable effect on the continuous natural reduction of the drilling resistance of the specimen over time. The results presented are of immense value to conservators as they provide essential guidance on the most appropriate repair approach. Impact to the conservation industry will be to avoid the use of nanolime on stones where there is no perceivable benefit, reducing the risk of adverse effects, including potential damage to buildings. In additional costs will be saved which might otherwise have been spent on ineffective treatments.

Highlights

  • Types of limestone such as Bath and Portland Stones have been used as a building material in the United Kingdom

  • Materials 2019, 12, 2673 (H2 SO4 ) contained in the rain dissolves the main component of the limestone leading to the precipitation of gypsum (CaSO4 ·2H2 O) which is a critical problem in the conservation of stones exposed to the weather, because its crystals are highly soluble and have a volume up to 30% larger than the volume of the original matrix where they can exert pressure on the pore walls inducing micro-cracking [1,2]

  • A similar trend can be observed for. Both samples of Barnack stone were characterized by a harder crust on the both samples of Magnesium limestone that, as well as Barnack, developed a harder crust on the surface and this may have affected the penetration of nanolime

Read more

Summary

Introduction

Types of limestone such as Bath and Portland Stones have been used as a building material in the United Kingdom. Very often such stones are subject to decay that can alter their aesthetic, physical and mechanical characteristics and, in some cases, their stability and the stability of the structure they belong to. Various mechanisms contribute to the stone decay It is known, for instance, that in urban environments, atmospheric pollutants such as sulphur dioxide (SO2 ) and nitrogen oxides (NOx ), and the resulting acid solutions produced in the atmosphere (i.e., acid rain) play an important role in accelerating the decay of limestone used in historic buildings. If the stones are exposed to cold and wet environments, freeze-thaw cycles can subsequently contribute to the degradation of the stone’s matrix, leading to weakening and eventually spalling of the stone surface or even shattering of entire blocks

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call