When cross cutting treated timber, it is standard practice to treat the cut end with a brush on preservative. For roofing applications the advice can be varied, as the risk of the treated batten decaying within the roof space is minimal.
However, the advice is different at the verge, especially when the batten is bedded into mortar. The most simple method is to turn the batten so that the treated end is bedded into the mortar and the cut end within the roof space. If this is not practical, then the cut end must be treated.
Marley Eternit recommends the use of Osmose End Coat WB.
The treatment is specifically designed for this purpose and is suitable for all roofing battens. The formula used is water based so that it has no effect on the underlays (some treatments are solvent based which could adversely effect roofing underlays).