Tanalised decking boards. 3.9m 120mm x 28mm. Treated Decking provides an excellent alternative to a paved patio area. An attractive addition to your garden space thus ideal for al fresco dining and BBQs. Wood naturally rots over time. By treating the timber, we are able to slow down that process and extending the longevity of the decking. So as a result, treated decking requires less maintaining.