Causal agent
decking
Brown rot decay of cedar wood on exterior decking
Fri, 05/07/2010 - 18:53 — jhelsethI. Title: Brown rot decay of cedar wood on exterior decking
II. Deterioration Agent: A brown rot fungi
III. Location: Minneapolis, MN, USA
IV. Description of Problem: Brown Rot
This house was constructed in 1856 and resides near the University of Minnesota. It served as the home for the University of Minnesota’s first president and is one of the oldest homes in Minneapolis. It is now home to the Minnesota Alpha chapter of Sigma Phi Epsilon Fraternity. The house joined the Minneapolis Heritage Preservation Commission in 1976. It suffered a devastating fire in 1992 and portions of the house were rebuilt shortly after. There are multiple areas around the exterior (mainly the front and back porch) that suffer from brown rot decay. The re-construction of the front and back porch could have led to and or aided in the problems described below. The carpenters may have not used properly treated wood, they may have not dip-treated the ends of the boards if they had been cut to size, they used iron nails which could have been a point of entry for the fungus, and may have not taken ground moisture or rain drainage into consideration. The main area of rot occurs at the junction between the porch and a custom made pillar. Due to the custom woodwork, it is possible that the carpenters did not properly treat/close all seams and edges. There are no sporophores present but the brown rot can be identified by the presence of cubical checking, the deep brown color from the remaining lignin, and the ability to crush the wood in between fingers which forms a powder. There is also galvanic corrosion present on all of the nails. The Fenton reaction between the fungi and wood causes an early and rapid strength loss by hydrolyzing cellulose and hemicelluloses. The rapid strength loss of the porch proves to be dangerous for anyone walking on its surface. Due to this fact, the structural boards, the decking boards, and the custom pillar need to be replaced. The Heritage Preservation Commission requires that the façade stay identical to the original design. This makes replacing these exterior structures more difficult due to the cost and expertise required to meet the Commission’s standards.
Avoidance Strategy:
Make sure wood is re painted as necessary and completely applied to all wood surfaced. Ensure all debris is cleared from underneath porch. Make sure snow and ice are removed from the porch before the spring melt. Check wood pieces that have ground contact to see if it is vectoring the fungi. If yes, replace those boards and if not, ensure the ends are properly treated. Inspect annually to ensure the prevention of future degradation.
Remediation Strategy:
The structural boards and the deck boards need to be replaced. Naturally durable and decay resistant lumber is an option although it is believed that the current wood is cedar and has decay. The structural lumber should be a minimum of .40pcf and the deck boards should be .25pcf, fully painted, or stained. If the boards need to be cut to size, the ends need to be painted, stained, or treated with a copper based preservative such as copper napthenate, copper azola, or ammoniacal copper quat. This will help fight against decay but may discolor the wood or have an unpleasant smell, such as diesel. If the Minnesota Historical Society had more relaxed regulations, wood-plastic composite decking could be used. Other strategies include using stainless steel or galvanized nails and limiting moisture. Moisture can travel from the ground, up through the wood, and to the top of the deck structure so make sure grass and leaf debris is not present. Also, make sure all gutters are working properly to avoid rain or snow melt coming into contact with the structure.
Juvenile wood related breakdown of treated wood in decks
Mon, 07/20/2009 - 21:45 — jwinandySometimes 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.
Avoidance Strategy:
Avoid juvenile wood for the top decking when at all possible in building treated wood decks. Another more practical solution is to regularly treat the decking boards with water-repelant treatments.
Remediation Strategy:
When the problem first is noticed, begin a regime of regularly treating the decking boards with brush-applied water-repelant treatments. If the problem becomes extensive, replacement is the most practical solution.
