TANNIN WARNING Kwila's superior strength and stability are attributable to its tannin-rich properties, resulting in low shrinkage and minimal surface and end splitting. Tannin is a naturally occurring substance in timber which will leach the first few times it is exposed to moisture, staining timber, paved areas and other nearby surfaces. Objects left on the timber surface will also draw tannin out, creating surface marks. A thorough and regular hose down during the first few days will assist in flushing excess tannin away and minimise subsequent staining.