Renere teknologi til undgåelse af biologisk vækst på murværk, tegl- og betontage
Summary and conclusions
Background for phase 3 of the project – Test methods
In phase one of the project, agents and methods used for cleaning were investigated, and phase two examined the organisms actually living on the surfaces of buildings. In this phase we wanted to test the effect of agents and methods under controlled conditions, primarily because there is no tradition for documenting the effect of chemical cleaning agents, surface agents or methods to prevent or control biological growth on outdoor surfaces of buildings. The project was limited to masonry, clay, and concrete tiles.
Scope
The aim of this phase of the project was to develop a laboratory method to test agents and techniques used to prevent or control biological growth on bricks, clay, and concrete tiles. Both the effect of different types of biological growth and the physical parameters of the materials were included.
The following work programme was made:
 | A literature review to investigate whether existing tests may be relevant in connection with the current test. |
| Preparation of a standard laboratory test method to test agents and products. |
| Testing the draft standard and adjustment in the laboratory. |
| A draft method for testing mechanical cleaning on the basis of existing knowledge and the results from this project. |
| Development of a technique for quick examination of biological growth. This technique may be used in connection with field-testing, in-situ testing, and quality control. |
Definition and approach
In the project the term "biological growth" was used to cover growth of:
| bacteria |
| algae |
| fungi |
| lichens |
| mosses |
Higher plants such as facade plantings were not included in this project.
The project only includes organisms that can grow in Denmark on the materials mentioned below:
| masonry materials including |
– bricks
- calcium silicate bricks
- granite/gneiss
- masonry mortar
- rendering mortar
- whitewashed masonry surfaces
- painted masonry surfaces
| clay tiles |
| concrete tiles |
Emphasis was on bricks, clay and concrete tiles.
The project distinguished between the following life cycle phases for masonry and roofs:
| Extraction of raw materials |
| Production of building materials |
| Design |
| Construction/execution |
| Use/maintenance |
| Demolition – recycling/reuse |
Summary
It is desirable to develop methods for documentation of agents’ abilities to prevent and control biological growth. Also the resistance of different materials to biological growth may be tested.
Therefore a literature review of excising methods was conducted. Official standards do not exist, but in several countries, including Denmark, tests and projects have been described in the literature and in commercial reports. This information was collected and organised (see appendix 1). None of the methods in the literature were described in sufficient detail that they could be used as a standard. On the other hand the information may act as inspiration when choosing and developing methods. For example to evaluate materials’ resistance to deterioration or the controlling effect of agents in outdoor exposure.
Development of test method
In this project a method described by Grant & Bravery (1981) was used as a starting point to develop and test a new method. The original method was changed in several ways, e.g. expanded to cover several purposes, and simplified by using a monoculture of green algae instead of a mixed culture.
The new method was described using the format for standard tests.
The primary test organism, Stichococcus bacilaris Nägeli, was chosen on the basis of knowledge at the Danish Technological Institute (DTI) and the results obtained during this project. S. bacilaris commonly occurs on building materials and is easy to culture under laboratory conditions. Facilities to culture algae were established and several growth conditions were optimised. For example S. bacilaris grows best when pH is above 7, and pH in the growth medium is influenced by nutrients in the medium and the age of the culture.
Several materials were tested as a surface for algeal growth: bricks, concrete, and a slab material. The surface structure and the porosity of the material are very important for the development of algeal growth.
The colour of the material is important when evaluating the growth visually. Among the materials tested, the cellulose reinforced calcium silicate slab gave reproducible uniform growth, which was easy to register visually. Therefore, this material was suggested as the primary test material.
Evaluation of the test method
In order to test the method for different applications, and if necessary make corrections, a limited study of selected agents and materials was performed. This was done to test the method and cannot be viewed as a test of the agents and materials involved.
The method was tested with the following aims:
| To test agents to maintain or clean masonry, tile, and concrete roofs. |
| To test agents to prevent establishment of biological growth. |
| To test the resistance of materials to biological growth. |
Two cleaning agents were tested according to the manufacturer’s protocol. The experiment showed that it was possible to produce uniform results on replicate items and that it was possible to distinguish between the different products.
Small-scale testing of a hydrophobic impregnate was carried out. The scope of the test was to investigate whether the method could track changes in biological growth caused by a physical change in the material. The test items were not artificially aged. It is important to note that relevant artificial ageing must be conducted when testing agents to prevent biological growth on materials.
Different untreated materials were used as control when testing the cleaning agents. In this way it was demonstrated that the chosen primary test slab, a cellulose-reinforced calcium silicate slab, supports good growth of algae in a relatively short time. It was also shown that there was a large variation in the amount of growth and how quickly it was established on different materials.
Thus, this method was well suited to test, e.g. product parameters concerning the surface of the material.
Quality control of cleaning
On the basis on the above experiment, in-situ testing and testing of techniques for quality control of cleaning were carried out. Using the techniques used at the DTI for detection and identification of fungi in indoor environments, small-scale experiments were conducted using Rodac plates containing specific media for different groups of organisms (algae and fungi).
The MycoMeter test, which is specific for fungi, was also used. Rodac plates are pressed against the surface in question so spores or fine parts of the organisms present are deposited on the plates. The plates are incubated and depending on the specificity of the medium, fungi or algae will grow. In this way it is possible to test organisms present on a surface, even though they are not visible. The MycoMeter-test is based on an enzymatic reaction specific to fungi.
Both techniques were tested in small-scale experiments with chemical cleaning of masonry and concrete sills with biological growth comprising a mixture of algae, fungi, and lichens. The experiments showed that Rodac plates containing a specific medium might be used to control the quality of cleaning of plane surfaces containing biological growth of algae and fungi. The technique may be used in laboratory testing, field-testing and in practical testing of new cleaning methods or agents. Rodac plates are not suitable for growth of lichens or mosses. Further testing is needed to document the usefulness of this technique.
The MycoMeter-test was not appropriate for this purpose.
Test method for mechanical cleaning
A method for testing mechanical cleaning was described and tested. Calcium silicate slabs, different clay tiles, and concrete tiles were cleaned using a hot-water treatment. The slab material was injected with algae in the laboratory, while the biological growth on the other materials was established naturally.
The surface of the materials was examined before and after cleaning in order to detect possible damage to the materials and the effect of the cleaning procedure. After the experiment the slab material was re-injected in the laboratory, while the tiles were placed outdoors at a 45° angel. After six months biological growth was recorded visually. All red tiles had large amounts of algeal growth and minor amounts of lichens. On concrete tiles and the slab material no growth was recorded. The field experiment continues.
Results from phase 3
This part of the project has documented the need to perform evaluations of the effect of the methods and products on the market. Evaluation of the risk of changing the properties of the materials when using these products and methods is also required.
The results of phase 3 consist of:
| An overview of pervious test methods. |
| A standard for examination of cleaning agents, surface agents, and materials described and tested on selected products and materials. Also variations of the standard have been described and tested. These variations may be used to determine the actual test procedure for, e.g. a producer of an agent. |
| In connection with the above, standard facilities for laboratory testing have been established, including incubation with artificial light, constant temperature and moisture. Growth of monocultures of green algae has been performed to optimise the growth conditions. |
| A method for testing mechanical cleaning has been described and tested. Further documentation is needed. |
| A technique for either quality control of cleaning or to document the testing of mechanical cleaning was described and tested. |
With this basis it is possible to offer, e.g. producers of cleaning agents and paints, cleaning companies or producers of materials exposed to outdoor conditions a program for validation of their products’ effect on preventing or controlling biological growth on outdoor exposed materials. It is also possible to document the resistance of a material to biological growth.
Discussion
In this project focus was on laboratory testing using a monoculture of a green algae, instead of more time-consuming field tests. Ideally several biological test procedures, ageing procedures, and investigations of parameters of the materials should be combined. In each case the optimal test program must be put together. This project gives the basis for combining and performing a test program.
The project also initiated the development of a concept for quality assurance of cleaning of biological growth. The results from this project showed that the durability of materials is not shortened compared to the expected durability when growths of different organisms occur. Therefore care should be taken when treating materials with cleaning procedures, surface treatments, etc. without documentation for a long-term improvement and not just a short-term (maybe less than six months) cleaner appearance.
Conclusions
On the basis of the experience obtained from this phase and the project, we can conclude:
| There is a lack of well-documented chemical cleaning agents, whose effect has been tested when cleaning biological growth on masonry, clay, and concrete tiles. |
| Facilities and methods for biological laboratory testing exist, and it is possible to adjust the tests in accordance with the needs of the producer. |
| It is also possible to test the agents’ effect on different parameters of the materials. |
| There is a lack of documentation of surface-treatment agents. Examinations of the materials and artificial ageing must be included in the biological testing. |
| Finally it is possible to compare materials’ resistance to biological growth in laboratory tests and outdoors field tests. Visible growth of lichens and algae can be established in six months on aged or damaged materials. These tests can be used as documentation of single products or when developing new agents, methods, or materials. |