What is Dry Rot?

Dry rot is a destruction of timber caused by colonization with cellulose-eating fungi such as Meruliporia incrassata and Serpula lacrymans. When wood is colonized with these fungi, it becomes crumbly and brittle, eventually failing. This type of timber damage is a problem all over the world, and people use a number of techniques to combat it, ranging from treating wood with antifungal chemicals to using alternatives to wood for key parts of a structure to avoid damage caused by dry rot.

The term “dry rot” is a bit confusing, because it conjures up an image of wood which decays in totally dry conditions. In fact, in order for dry rot to occur, there needs to be an ample source of moisture, and the wood may be quite moist in addition to crumbly and slightly spongy. The “dry” is in fact a reference to an outdated term for treated timber. When timber is “wet” it is raw, without any treatments, while “dry” timber has been subjected to treatments to make it more durable.

Some classic places for dry rot to appear include the bathroom, the kitchen, decks, and outdoor stairs, because all of these areas tend to be high in moisture. In some cases, the outside of the wood may appear perfectly fine, but the inside is totally destroyed as the cellulose is eaten away. The first sign of dry rot may be the appearance of fruiting bodies on the outside of the wood, or an increasingly frail appearance in a piece of timber. When infected wood is handled, it tends to feel very light, and it crumbles away at a gentle touch.

When timber is continuously saturated, conditions are too wet for the fungi to grow. This approach to preventing dry rot is not recommended, however, as it has a number of drawbacks, not least of which is that it's not feasible to keep a structure underwater. Instead, timber should be kept as dry as possible. Ground to wood contact should be avoided, as the ground usually holds moisture which can permeate the wood enough to promote fungal growth. Proper ventilation is also advised, to keep things as dry as possible, and exposure to sunlight is also a good idea, as UV radiation kills many fungi. Wood can also be treated with antifungals to resist infection, although this method is not foolproof.

In the event that rot has already occurred, the damaged wood should be removed and replaced. Several companies make an epoxy which can be used to fill in areas which have been damaged by dry rot. It is also important to remove plaster and other accessory building materials when treating rot, as the fungi can be harbored in plaster, glues, and wallpaper.

Rubber can also be subject to a form of dry rot, which is caused by aging and dryness. Over time, rubber dries out and begins to crack and crumble. People can reduce the risk of dry rot in rubber products by replacing things routinely, and keeping them moisturized. Rubber conditioners are available for things like tires and the weatherstripping on cars.