research_rot

ROT JAR DECAY TESTING
Decay is an undesirable fungal infection that causes the weakening of wood and can cause severe structural failure, as seen with the dreaded leaking building syndrome. Decay leads to strength loss because fungi survive on the cellulose in wood, which gives the wood its structure. The Rot Jar Decay Test is a laboratory test used to determine the effectiveness of preservatives in preventing decay.

At Zelam the samples are prepared and treated in the Woodcare Research workshop. Formulations are tested at a range of concentrations and are compared with an accepted industry standard depending on the required hazard class, H3 or H4 etc. Sets of untreated samples are also included as blank controls.

When dealing with solid wood the treatment process followed is Modified Vacuum Impregnation. The samples are weighed before and after treating in order to calculate the exact preservative retention level. In the case of engineered wood products such as LVL and Plywood, samples are treated through the glueline or by the individual veneers. (Fig 1)

After treating, samples are put through a weathering or leaching cycle, to simulate rain and to monitor loss of preservative under these conditions. Once this is done samples are passed on to the Microbiology Lab to be sterilised and set up in the test environment i.e. the culture jars.

The jars are packed with sterilised soil at standard conditions with regards to pH etc. A section of culture medium, containing a species of either brown or white rot fungi, depending on the purpose of the test, is placed on top of the soil along with a feeder strip to encourage growth. The jars are sealed with a lid equipped to allow for sufficient aeration and are incubated at the desired temperature until sufficient growth of the inoculum is established.

In a sterile environment the samples are placed into the jars containing the growing fungus and incubated for a period of up to 24 weeks or for as long as the test requires. (fig 2) After the duration of the test the samples are removed from the jars, cleaned and weighed in order to calculate weight loss. (fig 3) The performance of preservatives is evaluated on the mean percent mass loss of the samples. -Tamara Henderson, Woodcare Research Technician

Results from a rot jar decay test (pdf)