Many of the timber products that we sell on GardenSite are manufactured from pressure treated timber. On some occasions a substance similar to mould forms on the surface but, as David Coton explains, this is harmless and easy to remove.
Timber products such as sheds, arbours and pergolas are pressure treated to maximise their resistance to rot and insect infestation, so increasing their life span.
The process involves submerging the timber in a container full of preservative solution. Pressure in the container is increased and the preservative forced into the wood.
After any excess preservative is drained, the timber is dried. It's at this stage that evaporating liquid leaves deposits on the surface of the timber.
These look like green/blue speckles (the same colour as the preservative) and can easily be mistaken for mould. Although when compared side by side, the difference between these speckles and mould is very apparent.
There's no need to worry as the speckles will disappear over time as the timber weathers. Alternatively, they can be removed either by pressure washing or light sanding.
During packing or storage, mould does sometimes occur if there isn't adequate air circulation. Again, this is nothing to be concerned about. The mould is only on the surface and not detrimental to the wood.
To remove it, just wipe with a damp cloth, brush or pressure wash the surface. You can also be reassured that when the product is assembled and in the open air, the mould will not return.