Spontaneous Combustion

Wood Finishing Without Flare

Though you are surely well aware of the hazards associated with finishing oils, it's worth a moment to review why drying oils such as linseed and tung oil (and products like Watco that are based on drying oils) must not be handled carelessly. After you've applied and then wiped off excess oil, the finish's mineral spirits vehicle evaporates rapidly and more or less harmlessly. As the oil resins cure, however, they absorb oxygen, releasing heat as a waste product. On a workpiece, that heat simply dissipates into the air, but if you wad up a used application rag so that it insulates itself, sufficient heat can build up to cause the rag to burst into flames. Oily rags must carefully be hung or spread out flat to dry, or they must be completely immersed in a water-filled bucket. Once they're dry there is no further spontaneous combustion hazard. Please take this warning note seriously. If you let the press of work or an untimely phone call or visitor distract you from handling application rags as recommended, you might well start a fire. Be careful!