Zprávy památkové péče 2018, 78(5):511-514 | DOI: 10.56112/zpp.2018.5.12

Available method for detecting the water absorptivity and wettability of historic plasters and masonry in situ

Dagmar Michoinová

NPÚ, GnŘ

The professional public is becoming increasingly cautious about the inconsiderate and widespread use of modern materials that fundamentally and irreversibly alter the original characteristics of historic building materials and that do not respect the constructional-engineering system of historic structures. This often evokes a conflicting response from unschooled designers or restorers of historical buildings, many of which are heritage protected. The application of bonders, and some fixing agents, which restrict the absorptivity of the masonry or plaster on historic structures, especially structures which are not insulated from rising moisture, is clearly a case in which caution is needed. It is therefore useful to know, and to be able to easily assess in practice, whether the application of the given agent changes the absorptivity and wettability of the substrate appropriately or fundamentally.
The article describes a simple method for assessing wettability and absorptivity in situ. This is a tool for determining the suitability of the intervention directly on site, ideally on samples of treated and untreated surfaces. The procedure works whereby a suitable amount of water is applied from a syringe onto a substrate at a tested speed under a tested application angle between the between the syringe and the substrate. The method is based on the different rates of water absorption into various wettable and absorbent plasters or masonry. The method allows for the comparison of the wettability and absorptivity of the surface before and after application of the bonders or fixing agents, since some of these agents greatly reduce the monitored properties of plaster and masonry, which is undesirable for sustainable care especially for non-insulated historic buildings. After using the method for a longer period and learning its advantages and limitations, the method of assessing wettability and absorptivity can be used in situ for other more complex assessments such as comparing the absorptivity and wettability of supplemental plasters or when searching for the cause of damage to masonry and plaster. This method does not give absolute values of absorptivity or wettability. It is, however, a very simple and usable method to use in situ, which is its main priority.

Keywords: historical plaster, historic masonry, absorptivity, wettability, penetration, in situ tests

Published: December 1, 2018  Show citation