Timber Leaching

Timber leaching or tannin leaching is a common problem with timber however its quite easily fixed.


Tannins are an organic substance present in some timber species, especially those grown in tropical areas. Tannins are stored in the cell structure of the timber and as they are water-soluble they generally wash out through the end grain of the timber which can stain the surrounding surfaces, especially light coloured, porous surfaces like paving or rendered walls. Mostly tannin leaching will slowly disappear over 4-5 months.


Thankfully, being water-soluble, tannins can generally be cleaned with soapy water if attended to quickly, if left for a longer period of time a oxalic acid base timber cleaning product may be required. Whilst we don’t recommend a particular brand you can search for ‘timber tannin remover’ or timber cleaning products are available from most hardware stores.


Prevention is always better than cure however to completely eliminate tannin leaching is difficult but it is possible to reduce leaching. Tannin also reduces over time and generally lasts up to 4-5 months depending the level of moisture the timber is exposed to. Listed below are some methods that reduce tannin leaching:

Sealing the end grain of the timber using our proprietary aluminum trims with a sealant to keep tannins in. Below is an example of our Trendplank timber cladding using an aluminium L angle with a foam gasket and sealant (Sealant can be Sika 11FC or similar) to seal the timber end grain.

Another effective method to reduce tannin leaching is to use a tannin remover on the timber which draws out the tannin from the timber before you coat the timber with oil. While this method can be messy and require clean up it substantially reduces the tannin in the timber so the tannin is less likely to leach out over time. There are many tannin removers available, we recommend you search for ‘timber tannin remover’.


No, some timbers leach more than others. Australian species such as Spotted Gum and Blackbutt and other hardwoods, including, Pacific Teak and Merbau, are more susceptible to tannin staining. Timbers like Burnt Ash has been thermally modified, this process removes almost all of the tannin which means leaching is highly unlikely.

The team at Mortlock Timber are able offer advice to eliminate concerns relating to timber leaching for your project. Get in touch!