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Hydrophobic coatings for facades of concrete and rendering - an investigation into the effects on transport of moisture

Obtaining information on how water repellents and visible
coatings can be used in combination in order to control the
transport of moisture in and out of the outermost layers of
facades made of concrete and/or rendering.

The project comprises material systems for exterior facades, composed of concrete and rendering at the substrate and surface treating materials of two main types; water repelling impregnating agents and surface coatings with a visible film (paints and related coatings of organic and inorganic binders). The research involves extensive comparison measurements to be carried out in order to obtain data about the water transport properties of such surface material systems, which are considered to be of importance in reducing damage that occurs in painted cementious facades. The main experiments will be carried out on numerous test pieces in "Spray-Dry Towers," simulating rain and wind drying in the laboratory. The test pieces will mostly be cut as regularly shaped stones, from "Facades" specially built of the various substrate materials and surfaced treated more or less at conditions known in real situations. The experiments will be based on measurements of the quantities of water absorbed through and released out through the test surface of the treated stones under various parameter combinations from the following three categories: 1. Surface treatment material systems, i.e. various combinations of water repellents and paints. 2. Substrates of various types and properties W.R.T. water absorption and inner conditions such as water content and temperature. 3. External conditions, i.e. cycles of various combinations of wet and dry periods. The wet conditions involve water spraying, the drying conditions involve various combinations of air humidity, temperature and speed. For correlation purposes, test pieces subject to exterior exposure will be selected. The idea is that the results will be used as information basis for the development of: a. better functionally oriented products, b. test methods simulating natural conditions, c. practical descriptions of durable material systems for improved protection of facades. A preparatory project has already been completed. In the same way as this main project, it was supported by THE NORDIC FUND FOR TECHNOLOGY AND INDUSTRIAL DEVELOPMENT (NI). The total cost of the prepatory project amounted to about 100 ECU. Its chief objectives were to obtain basic information regarding technical details for carrying out the main research experiments. It involved: a. the development of experimental equipment and a comparison method based on the idea of using "Spray-Dry Towers," b. experiments designed to find out whether the parameters involved could be reduced in number, which was found to be the case, c. experiments aimed at providing data for the detailed planning and organising of the main project, as well as for correlation purposes. As to the project background, there are indications that painted facades can be made quite hydrophobic in a very favourable way by means of certain combinations with water repellents. In overwhelming cases where concrete and rendering are damaged by "Natural" forces, water or moisture plays an important role among the causes. The same applies when the problems are malfunctions, rather than damage, such as efflurescence and reduced insulation properties. Polluting chemicals also normally require water for their damaging effect, e.g. the acidic ones. It is therefore of considerable importance to be in a position to control the moisture level in these cement based materials, especially when their quality is not first class as often turns out to be the case. In such situations protection can be essential and it is often approached or attempted by means of surface treatment. On the contrary, concrete and rendering surfaces often are treated with coating materials, of widely varying types, purely for aesthetic reasons. In such cases, if the quality of the substrate is such that it is not thought to require protection against e.g. rain water, questions of another kind may need consideration: What surface materials will best fulfil the aeshetic requirements without the risk of being detrimental to the substrate? Some coatings may disturb the dynamic moisture equilibrium between a cementious facade and the exterior atmosphere or the ever changing weather conditions. A coating may, for instance be a barrier against the diffusion of water vapour out of facades, without being a very good barrier against rain water. Prolonged wetting of surface films may cause strong water absorption into the concrete or rendering substrate. It has been shown by systematic measurements of moisture in a number of real facades of concrete and rendering, extending over a few year periods, that the application of water repelling agents alone can effect a considerable reduction in the moisture level. The presence of many types of paint films on top of water repelling agents can, on the other hand, lead to a considerable slowing down of the process of "Drying-Out" of facades. Paint films without e.g. "Priming" with a repellent may not bring about a reduction in the moisture level at all.
Acronym: 
CON-COAT
Project ID: 
664
Start date: 
01-01-1991
Project Duration: 
33months
Project costs: 
300 000.00€
Technological Area: 
Market Area: 

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