Compatibility and performance criteria for nano-lime consolidants

For the conservation of decayed stone in monumental buildings, especially for damage types like sanding and powdering, industry has developed consolidating products. Ethyl silicates (silicic acid esters) have been used for a long time. Quite recent is the development of nanolime based consolidants for the treatment of limestone and mortars.
The EU Nanomatch project aims to develop nano-lime based consolidants for limestone and for substrates like (lime based) plasters and mural paintings; in a parallel development, which is not dealt with in this paper, also wood and glass are taken into account.
In the framework of this project, compatibility and performance criteria have been formulated and the methods to assess these have been identified. In this paper an overview is given of the most important criteria; some initial test results of substrates treated with both commercially available and prototype-products under development in the Nanomatch project (indicated as Nanomatch 1, 2) are shown as an illustration of some of the methods to assess performance.
For compatibility, many definitions are around. Within the project, compatibility is defined as: a treatment can be considered compatible if it does not lead to technical (material) or aesthetic damage to the historical materials.. Compatibility criteria are related to the properties of the consolidated material with respect to those of the untreated material; performance criteria are related to the effectiveness of the treatment and include long-term behaviour, i.e. its durability. Technical requirements, i.e. further specification of compatibility and performance criteria, have been for as much as possible suggested, including indications on the methods and standards for their assessment.