How can I preserve an installed post from rot?

[gsm]

I have just finished installing post for decking stairs at front of house using 200 x 50 mm treated pine H4 sleepers. I have split the sleepers lengthwise into half and then installed in concrete, unfortunately did not oiled/used preservative to cut ends. is there something I can do now to prevent the post from rot. Your help would be highly appreciated. Thanks

[MitchellMc]

Welcome to the Bunnings Workshop community @gsm. It's sensational to have you join us, and many thanks for your question about preserving timber.

Since the posts a now concreted in, there's not much you can do about the cuts enclosed by the concrete footer. However, there is TWA Woodcare 300g Ecoseal Tanalised Timber Treatment which you can use on the exposed cuts.

The original H4 treatment is penetrative, so some of your cut sections will still be treated. However, Pine heartwood does not accept treatment particularly well, so there will be little to no treatment in some sections. 

Please bear in mind that sleepers are not structurally rated for construction. They are for purposes such as building non-structurally rated retaining walls and garden beds. If you've used these non-treated sleepers for a structural purpose, it would be worth considering rethinking your approach and using structurally rated H4 posts instead.

Please let me know if you have any questions.

Mitchell

[gsm]

Hi Mitchell,

thanks for your reply. I have installed 

https://www.bunnings.com.au/88-x-88mm-1-8m-f7-h4-kd-treated-pine-premium-post_p8423171   Next to old sleeper post. Hope it should be fine now. 
Just another quick question, I have installed retaining wall of 900mm high at front because my house is at height. Do I need to put weed mat inside of retaining wall before filling it with soil? I’m going to install Merbau decking outside to cover the sleepers. 

[MitchellMc]

Good move installing the posts, @gsm. Non-structural sleepers tend to warp over time, so I think the extra work is worth it.

You don't need to install weed matting, but it can assist with stopping debris from migrating through any gaps in the wall. The other option is drainage matting, which will filter any water or soil particles. If you'd like to stop dirty water from exiting the retaining wall and covering your Merbau decking, I'd suggest drainage matting as it filters to a higher degree.

Please let me know if you have further questions.

Mitchell