Biodeterioration Diagnostics Database

Sometimes treated and even untreated decking boards are used that contain varying degrees of juvenile wood.  Because juvenile wood shrinks longitudinally from 2-20x more than mature wood, decking boards with high-degrees of juvenile wood that are restrained by metal fasteners and that are regularly exposed to direct rainfall (wetting) followed by intense sunlight (drying) sometimes experience visual degradation of the top surface and later may eventually experience mechanical failure of the wood.

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. 

Softwood rounds used as a parking lot bumper near Jackson Hole, Wyoming showed signs of defibration on the upper surface. Salt defibration has been reported from Antarctica (Blanchette et al. Polar Rec 38:313–) as an unusual decay phenomenon, but here it is near 45 degrees latitude in the intermountain West of the Rocky Mountains. This defibration results in accumulation of wood fibers on the surface and exposes fresh wood to UV damage and more defibration. In this case, if there was any preservative treatment in the wood, this slow progressive decay could expose less resistant wood and hasten decay problems. The defibration may also be as a result of diffusible treatment chemicals. Although in historic objects and buildings this would be a worry, this process in low-value situations like this is mostly curious and perhaps useful to scientists interested in delignification processes. When I first looked at this 'fuzzy' surface and saw two furry mountain dogs playing around in the owner's cabin porch, I thought I was looking at dog fur, but you can see in the close-up photos that wood fibers are sloughing off. I would never have looked closer if I hadn't read about defibration in polar huts. This area in Wyoming receives 300+ inches (750+ centimeters) of snow annually, and this means the snow plow and the salt are nearly in constant action during the winter. This was on a gravel road portion, however, so it is unclear if salt would be used. Additionally, visitors using the parking lot probably stand on these horizontal rounds often (see the image of me performing my version of a three-point bending test). Salt or preservative chemicals (etc.) may help delignify the wood near the surface, a phenomenon that has been seen in Antarctica on explorer's huts exposed to salty air and wind, as well as in other sea-side areas I'm told . Here, this problem may be exacerbated in the high desert weather that can bake the surface. As in any situation, the size of the problem depends on the cost of the material replacement and the risk. Both are low here, so this is not a major financial loss or safety hazard. Instead, it is just a nice example of how learning about a problem common to one situation (windy polar buildings) can be useful for deducing similar problems occurring in new contexts (visitor-rich, landlocked Wyoming).

Untreated wood, most likely southern yellow pine, was used for steps leading up to the deck shown in the attached images. The steps were built in 1999 along with the house, and the decay problem was very advanced by 2004. The steps look like they were painted gray, but the paint has chipped and worn, exposing untreated wood. The deck itself was 0.25 pcf treated wood and, at the time of these photos, did not show signs of the fungus (sporophores, cubical checking, etc.). Clearly, the agent of decay is a fungus. The sporophore belongs to Gloeophyllum sepiarium, also known as the 'mazegill' fungus. You can see its sporophore as a rust-colored protrusion (a small shelf fungus) at the front end of the step. It is a brown rot, so the problem the landlord faces here is three-fold: 1) the steps need replacing, immediately, 2) the renters are at risk for falling through the deck because brown rot fungi reduce strength in wood quickly and 3) the mycelial mass of the fungus in this wood can act as a source for problems elsewhere, including the deck. Assuming CCA was the treatment for the deck boards (pre-2004), there should have been little leaching since being built and there is lower potential, but at 0.25 pcf, you could still have decay. Some brown rot fungi are more tolerant/resistant of heavy metals. Also, one of the images shows that the nail fasteners have failed, and they do not look galvanized, etc. There was likely galvanic corrosion and possibly iron leaching into the wood which, for iron-dependent brown rot fungi, may be a problem.