Causal agent
decay
Brown Rot Fungus at the Witch’s Hat Tower
Thu, 06/16/2011 - 20:55 — harr0028The "Witch's Hat" water tower is located at the top of the highest natural land area in the city of Minneapolis. It is one of the few original water towers standing today in the Twin Cities area.
The original tower was built in 1913 and had a holding capacity of 150,000 gallons of water. It was also intended to be a bandstand, but after musicians experienced difficulty in carrying their instruments up the inside spiral staircase, that plan was said to have been scrapped after the first gig. In 1955 the tower was hit by lightning and sustained substantial roof damage. The city subsequently scheduled it for demolition, but the neighborhood of Prospect Park successfully appealed to the city's Department of Public Works to preserve it.
In 1986 the tower underwent major renovation for its preservation because the wooden roof underneath the tiles had rotted. The roof was repaired at that time and, as can be seen by the current and original pictures of the tower, work has been done to the outer structure as well. It has been estimated that these renovations extended the life of the tower another 100 years. (Accessed April 10, 2011: http://www.pperr.org/history/thetower.html)
The current problem at the site is decay of the staircase leading up to the tower and erosion barricades surrounding the tower. The stairs are used to access both the tower and the lovely park that overlooks the cities of Minneapolis and St. Paul. The erosion barricades appear to have been placed to save trees and other vegetation from washing away down the steep embankment from the park to the road below. Both structures are visibly deteriorating. Cubical checking is apparent in many places on the stairs and on the barricades. The stairs crush upon impact in several spots. The visible signs of decay at the site point to brown rot fungus. The cubical checking, crushing on impact, unbleached decay sites and ability to survive changes in temperature and moisture levels all suggest brown rot. Abiotic factors such as weathering due to UV exposure and swelling and shrinking due to the temperature variance these structures are subjected through throughout the year in Minnesota may have predisposed the wood to rot. To back up the brown rot claim, it must be noted that soft rot fungi attack is often confused with brown rot. Soft rot can display cubical checking, as does brown rot, and can appear similar in color to brown rot. There are some defining characteristics, however. Soft rot displays diamond-shape cavities, which do not appear in brown rot. Also, brown rot crushes on impact due to the micromorphology of the rot, described below.
The visible signs of decay at the site point to brown rot fungus. The cubical checking, crushing on impact, unbleached decay sites and ability to survive changes in temperature and moisture levels all suggest brown rot. Abiotic factors such as weathering due to UV exposure and swelling and shrinking due to the temperature variance these structures are subjected through throughout the year in Minnesota may have predisposed the wood to rot. Micromorphology can make signs of decay that are not visible to the naked eye, visible.
The scanning electron microscope (SEM) image shows decay from a brown rot fungus: http://forestpathology.cfans.umn.edu/photos/SEM%20crushed%20brownrot.jpg
Brown rot attacks in two stages. In the first stage, fungal hyphae colonize wood rays then travel through wood cell lumens. These hyphae cross between cells via the starch-rich pits or by boring through the cell walls to reach another cell lumen. The fungus uses iron ions transported by the hyphae into or through the wood combined with hydrogen peroxide produced by the fungus to cut the cellulose and hemicellulose chains in the wood structure. The fungus then releases enzymes that work to break the smaller segments into glucose monomers. This two-step attack results in wood that loses strength quickly. These broken structures of wood cell walls can be seen in SEM images.
Avoidance Strategy:
To avoid this problem at the tower site in the future, it is recommended that all the wood stairs and retainer structures be replaced with a more durable wood species such as redwood or cedar. These naturally durable woods are high in extractives and are naturally decay resistant. As an alternative to using a naturally durable wood, which is very expensive, it is recommended that the structures be replaced with a less expensive pressure treated preserved wood such as a wood treated with an aqueous copper-based preservative at a concentration intended for ground contact. Although pressure treated or durable wood species may have a higher upfront cost, they can be well worth the investment in the long run.
Remediation Strategy:
Replacing the rotten wood is recommended to ensure the removal of the brown rot. The steps should be kept clear of snow in the winter and debris from falling leaves, sticks and blown dirt throughout the year. A sealant could be applied to undecayed pieces of wood. With much of the wood already noticeably decayed, this treatment would be risky as it would seal any existing fungus in, allowing it to attack even more vigorously.
Brown Rot Decay of Untreated Steps with Chipped Paint
Thu, 06/11/2009 - 14:43 — norcu003Untreated 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.
Avoidance Strategy:
In regards to avoidance, other than using treated wood or applying an effective layer of paint (perhaps with some treads to avoid wear) I would try to keep the grass mowed next to the steps, and I would remove the debris, especially woody debris, from under the deck. This material is in ground contact in the dark and will vector new fungi into the structure. Also, annually inspect the rest of the building for brown rot.
Remediation Strategy:
The remediation strategy is as follows. These steps should be replaced, along with the stringers. Following a do-it-yourself approach is fine, but the wood needs to be treated. This is especially true of the stringers, and if you cut them, the exposed untreated wood should be painted or Cu-napthenate brushed on. If treated wood is used for steps, be sure if it is cut to brush a treatment on the newly exposed wood faces. If the owner wishes to repaint, the paint needs complete coverage and a yearly inspection. I would personally use treated wood, 0.60 pcf for the stringers if possible, and make sure they are resting on something other than soil.
