Dugan and Anthony
Moisture Moisture is not a mechanism of deterioration, but it supports many forms of deterioration and is an integral component of weathering, decay, and insect attack. Moisture contributes to the weathering process by causing wood to swell or shrink, thus generating checks and splits as the wood fibers expand and contract. Wood that is not exposed to environmental weathering or in contact with a source of moisture can remain stable for decades or centuries. Wood that reaches a moisture content of twenty percent or more is at risk for decay fungi and insect attack. Wood with a moisture content higher than thirty percent has a high probability of decay and insect infestation. Mold and Mildew Molds and mildews are types of fungi that do not deteriorate wood but can cause surface discoloration (Fig. 4). Most molds and mildews are white, green, orange, or black and are powdery in appearance.1 If spores are present, they can grow very quickly on moist wood or wood in very humid conditions. Since the conditions that are favorable for growth of molds and mildews are the same as for more destructive decay fungi, the wood discoloring organisms should be considered as warning signs of potential problems.
Fig. 4. The back of a painted wooden grave marker with green mold or mildew growth.
Annual Journal of the Association for Gravestone Studies