Does treated timber stop rotting? (1)

30 May 2021
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United Kingdom
Hi all question,

I am looking to build a very cheap raised bed, but was looking at using maybe pressure treated timber or decking board as this seems to be the cheapest option. question is once its filled with wet soil will this just rot the wood or does the fact its pressure treated stop this?

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It will rot judging by the number of rotting decking board raised beds I see over my allotment. If you give it a good soaking with timber treatment you may get an extra year or two before they need replacing. Some plot holders line their raised beds with polythene and that seems to work well.
No! ;)

Treated timber will still rot, especially if in direct contact with damp soil; albeit at a slower rate than non-treated.
Fungal and insect attack will also still occur.
...And it depends on the treatment, creosoted sleepers last for years! :)

However, keeping the soil away from the wood with a membrane and not allowing the base to sit on bare soil (i.e. having concrete base and dpc, or free draining gravel/sand), will help to lengthen the woods life significantly.
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The only other suggestion I can make is to take a look at recycled polyethylene planks and stainless steel angle plate/fixings. It is heavy, and quite expensive, but it will never rot. That's why some councils are using it for park bench slats, planters, decking, etc. I have now used it on horse stable doors a couple of times - the urine plays havoc with natural timber but doesn't affect the poly at all. Can be heavy going for your tools, though, and it is heavy
I lined my seat area after using cement boards where contact with soil to slow rot.

that looks brilliant mate. might steal your design with the seating, im making it for my disabled mum so would be ideal for her. question is the cement board the same stuff you use typically for tiling or is it something else?
Yes , standard cement board, 6mm is thick enough. My seat is plastic decking boards, got a few cheap.

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