Biodeterioration Diagnostics Database

A)  Description of the cabinet condition and potential decay occurrences

Oak wood was used for the cabinet under the counter in basement bathroom.  As the cabinet was built by a professional wood furniture production company, I assume the wood was untreated before the coating was applied.  The cabinet was built in 1990 along with the house and the decay problem was found at very advanced stage by 2008.  Water marks together with a damaged coating were observed on the bottom corner of the right side of the cabinet and some black dots are spread on the surface of the cabinet along with the water mark (Figure 1a).  These were raised and looked like sclerotia or other fungal resting structures.  And under the microscope, when punctured, these released spores.

The possible occurrence of this situation is mainly due to the mop that used to be stored at the right side of this cabinet.  Not only because the moving of mop caused mechanical wears on the cabinet coating on the corner (Figure 1b), the mop also reduced the ventilation on this corner.  This together with the high moisture content observed in this bathroom (40-50% all year round), would explain how water got a chance to penetrate and accumulate within the cabinet wood.  Furthermore, heat outlets maintain a warm condition for living organism.  All these factors have provided the microorganisms a suitable living environment with suitable temperature and suitable moisture content.  When it comes to the food resource for these microorganisms, wood of the cabinet is a good choice.  Although oak wood is naturally resistant, over-exposing the wood in excessive water for a long period of time without coating would decrease the durability of this wood due to leaching, volatilization as well as oxidation of protection materials such as extractives and preservatives.

B)  Deterioration Agent Determination

In order to determine the microorganism that caused the decay, the deterioration agent was separated from cabinet surface and plated on agar.  After two weeks incubation at room temperature, the strains were examined under the microscope (Figure 2a).  A soil test of this organism is still in process. 

According to the observation, the agent of decay found most likely belongs to Aureobasidium Genus which is a type of saprophytic or weakly parasitic sapstain fungi, most probability Aureobasidium pullulans (1). The hyphae of this fungus are septate and not extensive. When the colonies are young, the mycelium is hyaline.  As they grow and mature rapidly, the hyphae become dark with age and showed a smooth black shiny appearance (Figure 2b).  Conidiogenous cells are not fully differentiated in these fungi, so no conidiophore is found under microscope.  By the side of the old mycelium lots of conidia are borne.  These conidia are subhyaline to dark, unicellular, oval shaped (Figure 2c).  Based on the field book, these conidia can produce other conidia and form secondary blastoconidia by budding from the old conidia (1).

C)  Possible Effect

This sapstain fungus will cause discoloration and maybe some disfigurement of the wood surface.  It is commonly believed that the sapstain fungi will not lead to a decrease in wood strength.  However, the result from our course projects shows that the wood infected by sapstain fungi is more susceptible to brown rot problems, which leads to server strength loss of the wood.  In this case, the counter which is supported by the cabinet is exposed to the risk of felling.  The other issue of this infection is that the sapstain fungi will increase the permeability and decrease the durability of this piece of wood which also deduce the quality of this cabinet.