A Review on Consolidants for Repair of Deteriorated Structures

    Sapna Ghai, Research Intern, Rajni Lakhani, Principal Scientist, S. P. Agrawal, Chief Scientist, CSIR-Central Building Research Institute, Roorkee.

    The concept of consolidation arises a possibility to keep the original artwork in original form. Hence, restoration process is the judgement of repair material which should be compatible with the existing building material. Substitute materials should be used if the appearance and properties of the historic materials matches closely and causes no damage to the remaining historic fabric. A variety of repair materials are available in market but difficult to select the suitable one. Now-a-days various inorganic consolidants, organic polymeric consolidants, and waxes for stone consolidation are available. Universal consolidant does not exist since many factors are to be considered in selecting a consolidant for a specific stone or other structure. Porosity, water absorption, water repellence, pore size distribution are different parameters which affect the performance of the consolidant used. This paper presents a review on different types of consolidants, their characteristics, behaviour and performance in brief.

    Introduction

    There are large number of buildings and monuments in the world reflecting our cultural heritage. Most of these building are made up of different types of stones, jointing beddings and plastering material. But most of these buildings are getting deteriorated and mostly main cause of their deterioration is the environmental conditions. These environmental conditions are classified as (a) physical factors (temperature, wind, moisture penetration, solar radiations, capillary action etc.), (b) chemical factor (sulphate and other pollutants which forms acid with water i.e. acid rain), and (c) biological factor (botanical agencies such as vegetation, micro-organisms and zoological agencies as bats, insects, birds, animals).

    There is always a need to invent some restoring methods and materials for consolidation so as to protect heritage structure from further decay. Often the conservator or heritage preserver confronted with the decision of removing a heavy deteriorated zone and replaces it with a replica. Matching of replaced part or component with the original artwork and former ensemble suffers a tremendous loss of authenticity, which is a major problem envisaged. The concept of consolidation arises a possibility to keep the original artwork in original form. Hence, restoration process is the judgement of repair material which should be compatible with the existing building material. Substitute materials should be used if the appearance and properties of the historic materials matches closely and causes no damage to the remaining historic fabric. A variety of repair materials are available in the market but difficult to select the suitable one.

    It is important that the purpose of repairing damaged features and of replacing lost and irreparaibly damaged ones is both to match visually with what was there originally and to cause no further deterioration. For these reasons, it is not appropriate to cover up historic materials with synthetic materials that will alter the appearance, proportions and details of a historic building and that will conceal future deterioration. Due to many early failures of substitute materials, some preservators are looking for the materials that match the historic materials to restore historic buildings accurately and to avoid many of the uncertainties that come with the use of substitute materials. It must be ensured at the time of selection of any material for the restoration purpose that what should be done with the deteriorated structure i.e. consolidation and/or preservation. Coatings are mostly applied as preserving means and to stop further decay for protecting stone from externals. Consolidation on the other hand aimed to stabilise the friable material still allowing weathering to take place as a result of natural processes and at a natural rate. Consolidation should not be considered as a single operation for restoration of deteriorated structures. It is a part of a series of processes which include diagnosis, cleaning, pre- consolidation, consolidation, surface protection, and maintenance. Additionally, consolidation should be performed only in specific cases when the degree of deterioration threatens the integrity of the material.

    Now-a-days various inorganic consolidants, organic polymeric consolidants, and waxes for stone consolidation are available. Universal consolidant does not exist since many factors are to be considered in selecting a consolidant for a specific stone or other structure. Porosity, water absorption, water repellence, pore size distribution are different parameters which affect the performance of the consolidant used. This paper describes different types of consolidants, their characteristics, behavior and performance in brief.

    Consolidation

    Generally, the restoration process involves two distinct aspects:
    • cleaning the work of art so as to remove the unwanted / decayed materials and
    • consolidation process which involves the fixing or injection of substitute material in a way to prevent its degradation
    Now-a-day, gels are becoming most important tool for the cleansing of work of art to clean the dirt from the surface. The oil in water micro emulsions, several surfactants have also been used [1].

    Large number of stone consolidants such as inorganic consolidants, organic polymeric consolidants, waxes are available now-a-days. A review of state of art on above said different types of consolidants is as under.
    • Concrete Based Consolidants
    • Polymeric Consolidants
    • Nanoparticles as Consolidant

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