DEVELOPMENT OF ALGAL RESISTANT SURFACE COATING FOR EXTERNAL WALL OF BUILDINGS IN THE TROPICS WITH PARTICULAR REFERENCE TO THE BUILDINGS AND ENVIRONMENTAL CONDITIONS IN SINGAPORE

Abstract

The objective of this thesis is to find a solution to the disfigurement of buildings in Singapore caused by micro-organisms which is costing tens of millions of dollars every year in maintaining the aesthetics of the building facades. The major causes of the disfigurement have been identified to include : a) effects of climatic stresses b) kind of fouling micro-organisms c) detailing of buildings d) quality of substrate e) quality of paint f) painting specification The solution to this problem requires close coordination and cooperation among many parties concerned. The architects for their design of the buildings, the contractors for preparing the substrate and painting, the paint manufacturers for their paint and owners of the buildings for their understanding and acceptance of the causes and solutions to these problems. This research also studied the growth characteristics of the main alga, Trentepohlia odorata, in defined culture media with various enrichment nutrients in order to control its growth. Our objective was to develop an effective algal resistant emulsion paint that could be used for this purpose. The key tasks appeared to identify appropriate paint ingredients, including binders and algicides, and formulation parameters, that satisfied the following requirements: a) compatibility among the ingredients b) environment friendly c) commercially available d) economical e) can withstand the fairly extreme climatic conditions for five years or more. A few promising algicides were studied. Barium metaborate was found to be the most suitable for this purpose. Copper compounds, although effective in many cases were found to be generally not compatible with emulsion paint formulation. Although fourteen algal species were identified to colonise the facades of local buildings, it was only necessary to work on T. odorata. The tasks involved were divided into two main categories : a) In the laboratory b) In the field In the laboratory Two enrichment chemicals, namely sodium hexametaphosphate and potassium acetate, were identified for incorporation into the culture medium for the alga. Removal of copper from the Bold Basal Medium (BBM) increased the culture yield. The algal resistance test was conducted in petri dishes. Preageing of the painted petri dishes was conducted in a weatherometer simulating sunlight and condensation. Correlation of laboratory results and performance of paint on buildings was established. Concepts of paint formulations were introduced. A prototype paint was formulated at a low level of pigmentation coupled with the use of alkali and solar ultraviolet radiation resistant water-based binder and low-leaching and efficacious algicides. Water-based binder was chosen because of its being free from fire hazard and being environment friendly. Performance of the prototype paint was validated through two series of outdoor weathering tests to screen the durability of the paint film against mechanical breakdown and against algal growth. Environment of the two test sites complement each other for the two weathering test. In the field One of the most difficult tasks for a study of this nature is to get parties concerned, the building owners, the architects, the contractors and the paint manufacturers to share responsibilities to do a large scale field test simultaneously when the laboratory tests were being conducted. This is because uncertainties and high economic risks are involved which are often beyond the responsibilities of most individuals. After much persuasion to the parties concerned, eight buildings were selected for these studies. Performance test of the new paint culminated in a six-year life test by full painting to these buildings. The paint survived six years with impressive results against an expectation of three years for conventional emulsion paints. This exercise also shows that the new water-based emulsion paint is cost effective and can outperform solvent borne paints. The results of this project has been adopted and incorporated into a Singapore Standard for algae resistant emulsion paint, the first of its kind for the tropical region.