I thought that it was worth sharing a customers unfortunate situation with regards to treating wooden decking.
Having laid a beautiful deck the whole area needed treating and a really good oil from Osmo was choosen. All well and good. However, with the ‘summer’ that we had, the deck was sodden, so even though the day choosen to treat was a dry one the wood had not recovered from the deluges it had experienced for weeks prior to this.
The moisture level in the wood was so high that the oils could not penetrate as they would normally. This meant that the oil acted more like a paint than a wood oil. It therefore took longer to dry and also formed a glossy coat on the surface rather than the matt / silk finish that was desired. Not a happy customer and also left with a situation that was difficult to rectify without complete removal.
The people fitting the deck were professionals, but the pressure of time etc meant that they just got on with the job rather than thinking about moisture levels in the wood. Ideally the moisture content should be 20% or less. So if in doubt, check the wood with a moisture meter first to ensure that the treatment used will work properly.
We would also recommend treating the decking before it is laid down. This will allow you to treat the underneath and this helps balance out breathability of the timber. This makes it more stable in the long run. Also we would recommend that you treat any ends / cuts so that you protect these most sensitive of areas of deck. This might mean being around when it is being installed and / or giving clear instructions to the installers so that it does actually get done.
At the Eco Home Centre we would recommend using Osmo 4005 pre-treatments for any end grains (assuming the timber has already been tanalised – if it has not then treat all of the wood with this pre-treatment). Then an Osmo Wood Oil for a UV stable finish. You might wish to finish off with the clear Osmo Anti-slip top coat (430). However, remember that you need to ensure a low moisture content in the wood before starting any treatment. Good luck.