Some tropical hardwoods such as Merbau, Kwila and Kapur contain extractives that are water solouable and can bleed or leach onto walls and pavers
Tannin bleeding from timber onto walls
Some tropical hardwood such as merbau, kwila and kapur contain extractives in their sap that are water soluble. These extractives are washed out of the timber by water (rain) and tend to stain the surrounding areas with an orange brown mark. This doesn't matter if the timber structure is free standing as the tannins are washed into the ground but if the structure is built next to or on top of a wall then the bleeding can leave a very unsightly and disappointing mess to deal with.
The unfortunate thing about these timbers it that they tend to keep bleeding until they stop, which can be a long time. Timber cleaning solutions, like Wattyl Weathergard Deck Clean, are good to wash the stains off with. You may have to use a scrubbing brush and some elbow grease but generally you can move the stain.
Most timber coatings state that you must wait until this leaching has ceased before scrubbing the timber with a cleaning solution, waiting for it to dry then applying the specified number of coats. There are some products, such as Cutek CD50 that will minimise the leaching by penetrating deeply into the timber and locking the extractives in.Share