INTRODUCTION 



Fungal defacement and deterioration of organic coatings occur at 

 Naval installations around the world. It is especially severe at 

 tropical and sub- tropical locations. Economic losses caused by micro- 

 biological attack on paints and paint films in the United States have 

 been estimated to exceed one million dollars annually [1], This does 

 not include damage to substrate, such as communication equipment, 

 utilities, etc., which would greatly increase this figure. Thus, the 

 total annual damage may exceed several million dollars annually. 



In order to control fungal growth on exterior paints, additive 

 preservatives containing mercury have in the past been widely used. 

 Their use has now been restricted because of safety and ecological consid- 

 erations. Thus, the Naval Facilities Engineering Command requested the 

 Civil Engineering Laboratory to investigate the use of organotin resins 

 as an alternative method of controlling fungal growth. Such a method 

 might be much safer and could possibly provide longer protection than 

 those using additive preservatives. 



BACKGROUND 



Microbiological deterioration of paint has been classified into two 

 basic categories [2]. The first category is spoilage of liquid paint 

 (usually emulsion paint) generally by bacterial attack [3], resulting in 

 putrefaction and general breakdown of the paint. The second consists of 

 microbiological attack on cured paint films. The present investigation 

 is restricted to the latter category. 



Fungal growth on painted surfaces is highly dependent upon the 

 nature of the substrate [4]. This is believed to be related more to the 

 effect of the substrate on the environment (i.e., pH and retention of 

 moisture) than providing nutrient for growth. Thus, fungal growth is 

 generally greatest on painted wood, which has the high moisture retention 

 and no adverse effect on pH of surface moisture, and is the least on 

 painted metal and concrete. The infrequent occurrence of fungal growth 

 on painted concrete is related to the alkalinity the concrete imparts 

 [4], because fungal growth is greatly restricted where the pH of the 

 environment exceeds 8.5. 



The nature of paint is also an important factor affecting fungal 

 growth. The solvent evaporates on curing, and so is not a factor on 

 dried films. The pigment may inhibit growth by being toxic or by produc- 

 ing an alkaline environment, and the organic binder may serve as a 

 source of nutrient. There have been many reports [1] of fungal metabolism 

 of paint binders containing drying oils. 



