**4. Conclusions**

NIKU has treated distemper decorative paintings in 14 of the 28 stave churches, as well as in several other churches. The challenge of consolidating matte, water-soluble paint is finding a consolidation substance that binds loose paint and strengthens the paint layer without saturating the structure in such a way that it changes the look of the artwork. The consolidation agen<sup>t</sup> must be compatible with the binder in the paint; an ideal consolidant should have known ageing characteristics and preferably decompose naturally, thus making reconsolidation possible. First and foremost, an appropriate consolidant must conserve the paint layer. Since the early 1990s sturgeon glue has been the dominant consolidation medium because it changes the visual appearance of the distemper paintings the least; it is a natural adhesive substance which decomposes in the same way as the original binder and has strong penetrative powers and a high degree of adhesion at low concentrations.

The applied consolidation method with sturgeon glue works well for thin paint layers which need additional binding medium. The conservation of thicker distemper paint, for example where there are two layers of decorative paint on top of one another, is still a challenge and NIKU is still searching for a method that gives a good visual result, whilst adhering the paint to the substrate. The consolidation of thick paint layers is a problem in both unheated and heated churches, but experience shows that the thick paint flakes faster after treatment in heated churches. Recent surveys of the paintings in the nave and baptistery show that on the north wall there might be some locations with paint lose in areas with two paint layers, while the condition for the rest of the paintings in the nave and baptistery appears unchanged.

The RAT proposed by Anaf et al. in 2019, which was modified for distempered paints, demonstrated that the indoor climate of Kvernes—unperturbed by any heating system and still remaining in its so-called natural state-although not completely ideal, contributes to the preservation of distemper paints. Unsurprisingly, the indoor climate follows the outdoor climate without any control on keeping microclimate targets and/or reducing fluctuations and showed a limited number of risk periods for Kvernes over 2011–2012. This assessment, although not exhaustive of the impact of visitors or particle matter deposition phenomena, provides the potentiality to highlight at once the most and least favorable conservation conditions for distemper decorative paint over a typical calendar year. This type of understanding supports heritage managers and church owners in identifying risks situations and discriminating among the possible typologies of decay. In addition, the output of this analysis provides reliable information for supporting a risk managemen<sup>t</sup> plan for the preservation of distemper decorative paint. The SyMBoL project coordinated by NTNU is working for both the sake of cultural heritage and for those who want to experience the wooden construction and vivid colors.

### **Supplementary Materials:** The following SM are available online at http://www.mdpi.com/2225-1154/8/2/33/s1.

**Author Contributions:** T.M.O.: writing part in Sections 1.1–1.3, except for the first introduction, contributed to the editing of the text, contributed climate logger registrations in Kvernes stave church, contributed to Section 2, as well as discussion and conclusion sections. A.A.Ø.: contributed to Section 2, reference list, and responsible for figures. N.K.J.: contributed to the writing of Sections 1 and 2, contributed to reference list. L.d.F.: analysis and elaboration of microclimatic data from installed loggers, part of introduction section, result section on data loggers, and contributed to text formatting and editing. A.F.: writing of the abstract, and contributed text formatting, editing, and revisions. C.B.: paper coordination, risk assessment data elaboration and plots creation, writing of results and discussion and conclusions sections, contributed in the revision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by the Norwegian Research Council within the framework of the "SyMBoL— Sustainable Management of Heritage Building in a Long-term Perspective" Project (Project No. 274749).

**Acknowledgments:** The authors are grateful to Else Marie Bae of the Fortidminneforeiningen for her kind support during the monitoring campaign and to the Norwegian Directorate for Cultural Heritage.

**Conflicts of Interest:** The authors declare no conflicts of interest.
