Microbial growths and checking on acrylic painted tropical woods and their static bending after three years of natural weathering

Abstract

Wood products exposed outdoor could be weathered, especially in the tropical region with high in sun light, temperature, rain intensity, and relative humidity. Water based acrylic paint was coated on surface of teak, camphor, and pine woods for natural weathering resistance. The natural weathering and wood materials affected the resistance of the acrylic paint film on fungi (blue-stain and decay fungi), cracking, and MOE/MOR bending. After 36 months of exposure, the surface of unpainted pine and camphor panels were covered by fungi over 40% and reached the growth index of 5. The acrylic painted woods provided lower growths index of fungi up to three years of exposure. Application of the acrylic paint on the wood panels was observed to minimize the index of cracking from 5 for unpainted to 3 for painted after 36 month exposure. The average adhesion scale for the acrylic paint film dropped from 4.5 before exposure to 2.3 after 36 month exposure. The percentages of MOE/MOR drop after 36 month exposure were observed. The 36 month exposure caused the loss of MOR of 10.7% and 5.1% for unpainted and acrylic painted panel, respectively, and the loss of MOE of 6.8% and 1.4% for unpainted and acrylic painted panel, respectively. The acrylic paint film can be considered to protect the pine, camphor and teak at least 36 months. However, teak wood with the greatest resistance to the natural weathering factors will provide the longest service life compared to pine and camphor. Keywords: Acrylic paint, Tropical woods, Outdoor exposure, Mold and decay fungi, Climate index, Cracking, Bending strength