Historic Structures are commonly coated with mortar layers (plasters, renders, flooring) for protection and decoration. These well finished architectural stratigraphic surfaces often suffer from deterioration, such as lack of adhesion or detachment between support and mortar layers and even between mortar layers. Grouting and filling voids between delaminated layers can be an effective intervention if the layers are compact. This paper deals with aspects pertinent to the selection, design and implementation of a grout for the in situ stabilization and preservation of historic architectural surfaces. It presents the methodological approach, in accordance with the conservation principles, including sections on diagnosis, study and assessment of the deterioration phenomena, definition of grout requirements, selection of proper ingredients for custom-made or commercial grouts, as well as making and testing trial mixes, field testing and Assessment of the effectiveness of grouting. The aim of this paper, that is elaborated in the frame of RILEM TC 243 SGM, is to serve as a guide for users of lime-based grouts for the reattachment and reinstatement of historical architectural surfaces.

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For conservation interventions of historic masonry generally lime-based mortars such as pure air lime mortars, lime-pozzolan mortars, natural hydraulic lime mortars and ternary mortars (lime-pozzolan-cement) are used. The main reason is that their hygric and mechanical (strength and ductility) performance are easy to adapt to most existing historic masonry (compatibility requirements). Although the basic appropriateness of lime-based mortars for restoration is undisputed, there are also some limitations in the application of these mortars. In this report a review is given of the theoretical backgrounds and further of laboratory research developments in the field of lime-based binders and mortars over the past decades. Furthermore, practical experiences in positive and negative sense (damage cases) are elaborated. Drawbacks and points of attention are being dealt with, which are essential for a durable application of lime-based mortars for the conservation of historic masonry. In general, it is concluded that points of attention should be addressed through a thorough evaluation of their potential and through testing of their suitability. For these mortars, even more than for modern cement-based mortars, specifically, environmental exposure conditions and application conditions should be considered.

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The quality of repointing work in historic masonry is to an important degree determined by the composition of the repair mortar. Apart from this, good
workmanship is a basic requirement for durable repointing. Over the past decades
awareness has grown that the mortar composition of repointing should always be
considered and applied taking into account the hygric and mechanical properties of the existing adjacent materials. Often this is easy enough to realize. However,
choosing the composition of a repointing mortar there are situations where various damage risks seem to point at opposing materials properties. In the paper this problem is approximated analysing a number of damage cases with the aim to define more precisely which requirements and to what extent should be maintained. Subsequently, from lab studies and experiences with the application of natural hydraulic lime (NHL) in specific repointing projects a set of requirements is proposed. The context of this repointing study is repair of low-strength historic fired clay brick masonry in the coastal area of the Netherlands;@en

In this paper a pioneering, transparent restoration methodology is presented, introducing structural glass elements to substitute missing components of damaged monuments and simultaneously reinforce the original structure. To prove the feasibility of the concept, a damaged medieval tower in Toolse, Estonia is selected as a case study: Soil movements and over-consolidated clay layers result to a widening vertical crack, approximately one meter wide. Alternative designs, with float and cast glass components respectively, are proposed for restoring the crack and improving the wall’s stability. The considerable differences in strength and stiffness between the original wall and the glass addition require connections that establish a coherent system. Specimens bonded with selected adhesives are tested in shear and evaluated. Finally, full-scale prototypes of a characteristic part of the wall are produced and tested in three point bending to compare the overall cooperation and compatibility of each design with the medieval wall. @en

Factors affecting the design of repair mortars for historic masonry are: the type of masonry, the condition of the masonry and the exposure conditions. Especially in case of low-strength masonry exposed to heavy rain and high salt contents the design of a repair mortar may be a challenge. The most important problem is obtaining adequate insight into and feeling for the requirements, that play a role with regard to the mortar design. To this end the paper concentrates on materials behaviour of repair mortars in historic masonry. This is done in the context of the analysis of several types of attack on mortar durability: freeze-thaw cycling, salts, thermal movement, rain penetration. From this analysis relevant materials characteristics and technical requirements are derived. The main conclusions are

• the binder choice may significantly affect the durability of repairs,
• a basic and determining condition is a good execution technique.

Consequently, thorough insight into the characteristics and behaviour of the various available binders is then an important tool to the repair mortar designer. And, practical field experience with the possibilities and limitations of on-site execution practices may be very helpful to ensure good quality of the repair work.
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