applied sciences Review Selected Aspects Regarding the Restoration/Conservation of Traditional Wood and Masonry Building Materials: A Short Overview of the Last Decade Findings Radu Claudiu Fierascu , Mihaela Doni and Irina Fierascu * National Institute for Research & Development in Chemistry and Petrochemistry—ICECHIM Bucharest, Emerging Nanotechnologies Group, 202 Spl. Independentei, 060021 Bucharest, Romania; radu_claudiu_fi[email protected] (R.C.F.); [email protected] (M.D.) * Correspondence: [email protected]; Tel.: +40-727-860-186 Received: 17 December 2019; Accepted: 7 February 2020; Published: 9 February 2020 Abstract: Vernacular buildings are usually constructed using materials at hand, including wood, natural stone and bricks (either clay or mud bricks). All those materials are exposed to a series of environmental factors, affecting their structure and integrity. The literature review was conducted using different databases (Scopus, Web of Science, ScienceDirect, SpringerLink) using as keywords the historical material, “heritage” and the terms regarding the desired effect, within the envisaged time period (2010–2019). The assessment of the results was performed by manual inspection (reading the entire article) and the selection of the works to be inserted in the current review was made by evaluating the contribution to the field. This review summarizes different aspects related to the restoration and conservation of wooden and masonry elements of traditional buildings, including materials used for biocidal interventions, protection against abiotic factors, cleaning and consolidation agents. Finally, a critical discussion regarding the current limitations and future perspectives concludes the review work, envisaging the role of researchers specialized in materials science in the context of cultural heritage conservation. Keywords: vernacular constructions; wood; stone; restoration; conservation 1. Introduction Traditional buildings represent an important heritage of each civilization. These constructions are specific to each nation and region, considering a multitude of factors, including climate and availability of materials [1], without any one of them being decisive. Traditional buildings were usually constructed using the materials at hand, including wood, natural stone and bricks (either clay or mud bricks) [2,3]. All those materials are exposed to a series of environmental factors, affecting their structure and integrity. A good example of different construction materials can be observed in the Romanian traditional buildings (Figure1) which are usually consisting of a mixture of wood and masonry (either mud or clay bricks and stones). As the traditional buildings are considered to be a proof of continuity of a civilization [4], great attention must be given to the development of appropriate materials for their restoration and conservation. Appl. Sci. 2020, 10, 1164; doi:10.3390/app10031164 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 1164 2 of 28 Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 31 Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 31 Figure 1. Examples of Romanian traditional buildings incorporating didifferentfferent construction materials (stone,(stone,Figure bricksbricks 1. Examples andand wood)—pictureswood)—pictures of Romanian traditional belongingbelonging buildings toto thethe authors’authors’ incorporating privateprivate different collection.collection. construction materials (stone, bricks and wood)—pictures belonging to the authors’ private collection. Cultural heritageheritage of of a a nation nation is is formed formed not not only only of well-knownof well-known monuments. monuments. Traditional Traditional houses houses and theirand their constructionCultural construction heritage methods ofmethods a representsnation represents is formed an important not an onlyimportant legacy, of well-known whichlegacy, is monuments. transmittedwhich is transmitted Traditional from one generation fromhouses one togenerationand another, their which toconstruction another, was adapted which methods was to the representsadapted times andto an the needs, important times but and permanentlylegacy, needs, which but reflecting permanentlyis transmitted the environmental, reflecting from one the cultural,environmental,generation technological, to cultural,another, economic whichtechnological, was and adapted historical economic to the conditions an timesd historical and of needs, the conditions local but context. permanently of the local reflecting context. the environmental, cultural, technological, economic and historical conditions of the local context. The present review focuses on the recentrecent developmentsdevelopments regarding the materials used for the The present review focuses on the recent developments regarding the materials used for the restoration and conservation of traditional buildings (masonry, stone and wood) and represents a restoration and conservation of traditional buildings (masonry, stone and wood) and represents a critical discussion of aspects related toto theirtheir utilization;utilization; veryvery usefuluseful inin thethe transdisciplinarytransdisciplinary studiesstudies critical discussion of aspects related to their utilization; very useful in the transdisciplinary studies related toto furtherfurther developmentdevelopment ofof newnew materialsmaterials oror forfor thethe useuse ofof thethe currentcurrent ones.ones. related to further development of new materials or for the use of the current ones. The literature review was conducted using different databases (Scopus, Web of Science, TheThe literature literature review review waswas conductedconducted using differentdifferent databasesdatabases (Scopus, (Scopus, Web Web of ofScience, Science, ScienceDirect, SpringerLink) using as keywords the historical material (“wood”, “masonry”, ScienceDirect,ScienceDirect, SpringerLink) SpringerLink) using using as as keywords keywords the historicalhistorical material material (“wood”, (“wood”, “masonry”, “masonry”, “brick”, “brick”, “brick”,“stone”“stone” “building”, “stone” “building”, “building”, “mortar”), “mortar”), “mortar”),“heritage” “heritage” “heritage”andand the terms and regardingregarding the terms the the desired regarding desired effect effect the (“restoration”, (“restoration”, desired effect (“restoration”,“conservation”,“conservation”, “conservation”,“biocid*” “biocid*” or or “consolidation”)“consolidation”) “biocid*” or “consolidation”)within thethe envisagedenvisaged within time time the period period envisaged (2010–2019). (2010–2019). time periodThe The (2010–2019).assessmentassessment of Theof the the assessment results results was was of perfor perfor the resultsmedmed byby was manual performed inspectioninspection by manual (reading (reading inspection the the entire entire (reading article) article) and the and entirethe the article)selectionselection and of of thethe the selectionworks works to to ofbe be the inserted inserted works in toin the bethe inserted current review inreview thecurrent waswas made made review by by eval wasevaluating madeuating the by the contribution evaluating contribution the contributionto tothe the field field (the to(the theentire entire field process process (the entire is is described described process in isin describedFigure 2).2). in Figure2). FigureFigure 2. 2.General General procedure procedure followed followed forfor the selection of of articles articles to to be be included included in inthe the present present review. review. Figure 2. General procedure followed for the selection of articles to be included in the present review. Appl. Sci. 20202020,, 1010,, x 1164 FOR PEER REVIEW 33 of of 31 28 2. Materials Used for Restoration and Conservation of Wooden Elements 2. Materials Used for Restoration and Conservation of Wooden Elements 2.1. Biocidal Materials Used for Wooden Elements 2.1. Biocidal Materials Used for Wooden Elements Wood is considered to be one of the most common construction materials, with traditional Wood is considered to be one of the most common construction materials, with traditional buildings made of wood being encountered all over the world [5]. Due to its biodegradable nature, buildings made of wood being encountered all over the world [5]. Due to its biodegradable nature, wood is exposed to a wide variety of biotic and abiotic agents, including fungi, insects, termites, wood is exposed to a wide variety of biotic and abiotic agents, including fungi, insects, termites, moisture fluctuation or weathering [6]. Thus, the approach for restoration or conservation of the moisture fluctuation or weathering [6]. Thus, the approach for restoration or conservation of the wood wood artifacts should comprise two aspects: the biocidal treatment and a chemical consolidation artifacts should comprise two aspects: the biocidal treatment and a chemical consolidation approach approach (Figure 3). (Figure3). Figure 3.3. AspectsAspects covered covered by by the the present present review review regarding regarding the conservation the conservation and restoration and restoration of wooden of woodenbuilding building materials. materials. Another important biotic factor affecting affecting all the objects belonging to the cultural heritage is represented by by the the human human interventions. interventions. If we If speak, we speak, either either about about interventions interventions with negative with negative effects (througheffects (through the use the of use inappropriat of inappropriatee materials materials