As above, I am struggling to find brown treated timber for a fence in the required size (or anything even close).

Is buying sawn timber then treating it yourself going to be durable enough?

Buy pressure treated timber and then stain it.

Why?

Green -> brown is going to look duff (and not match the existing part of the fence)

Pressure treated will last years longer than anything where you’ve just painted a surface treatment on.

because pressure treating wood forces the preservative deep into the wood. painting a preservative on gets a few mm deep at best.

paint the whole fence if you want it to match.

Pressure treated will last years longer than anything where you’ve just painted a surface treatment on.

+1 – cut a pressure treated post across the section and see how deep the treatment goes compared to a surface stain. The base colour wont be noticable under a brown stain and even if it was i’d rather this than replacing the fence in a few years after it all rots through.

OK thanks all.

EDIT Ooh a question: I will have to cut down 150mm to match the 125mm I have. I am thinking cut at an angle and keep that edge down-facing so water doesn’t sit on it.

Is that better than a flat edge (not pressure treated) at the top?

Bump

just get 125mm… !!!

if you are going to paint slop it with creosote and used engine oil

will last for years that way

Cut edges into a bucket with 1″ of preservative in the bottom. Leave for half an hour (will wick several inches up the wood).