It's not uncommon for mould to grow on treated and non-treated timber. If the area is exposed to high moisture and brief sunlight it gives the opportunity for mould to develop. The mould you are currently seeing on your kid's cubby house is surface mould and will not affect the strength of the timber. However, it does pose a health risk if left untreated and can cause respiratory problems.

I suggest using a scrubbing brush and 30 Seconds to remove the mould from the surface of the timber. The shaded dark corners of the cubby house make for a perfect spot for mould to grow in. Once you've washed the cubby house, I propose painting the surface with Feast Watson 1L Clear Outdoor Furniture Oil or similar to protect the surface from regrowth. Either that or relocate the playground a little bit further away from the trees so that the entire set is exposed to full sunlight.

Please make sure to give the oil enough time to dry off before allowing the kids to get back to the cubby house. In the interest of safety, please make sure to wear proper protection such as safety goggles, gloves and a long sleeve shirt when painting with furniture oil.

If you have any other questions we can help with, please let us know.

Eric

woodalwaysworks

https://www.workshop.bunnings.com.au/discussion/comment/25006#Comment_25006

Thank you very much for the information EricL. I’ll definitely give it a try and let you know the outcome.
Many thanks

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