Answer
What is the difference between treated and untreated timber?
Treated timber resists rot and insects for outdoor use; oak and other durable woods last untreated.
In short
Treated timber is impregnated with preservative so it resists rot and insects outdoors, which is essential for posts, decking substructure and most garden joinery. Untreated timber, or a naturally durable wood like oak, is used where the species itself lasts. We specify the right timber for each job.
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