Tanalised Timber Rotting

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headey
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Tanalised Timber Rotting

Post by headey »

We have a log cabin that we built just 3 years ago. It stands on a frame of tanalised timber which, in turn, is standing on a base of MOT1 & slate chippings. The ground on one corner is higher than the base and soil had fallen to rest against the timber. I was surprised to find that the timber had already gone rotten. The photo I've attached shows it now: after I cut back the grass, removed the soil and filled the gap with gravel to prevent any more soil intrusion.

What is concerning me is that I had understood timber was tanalised to protect it from rot (or at least slow it down). Many gardening projects show tanalised timber used for decking and planters which is laid directly on or even in soil. If our exeperience is anything to go by, these structures could be useless within 2-3 years.

So, what is going on? Could it be that our timber is faulty? Having removed the soil and hopefully prevented contact in the future, will the foundation frame survive?

Does anyone have any suggestions/explanations/recommendations?
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aeromech3
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Tanalised Timber Rotting

Post by aeromech3 »

If you had cut the timber to length and not treated the end grain, then this will occur within 3 to 5 years. Incised treated wood has a better chance and this is how good wood fence posts are treated but even then there is a limit to how far the preservative seeps into the wood, when yours dries out, yes when, you need to treat it. One product for this is Ronseal wet rot wood hardener.
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big-all
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Tanalised Timber Rotting

Post by big-all »

pretty much what you expect with timber in contact with the ground treated or not
lots off things effect what happens around 19 % moisture it will rot
constantly soaking wont rot as easily constantly changing from say 15-22% will be fine but not holding constant
timber is best off the ground
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headey
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Tanalised Timber Rotting

Post by headey »

Thanks to aeromech3 and big-all. As the rot is at the end grain, then it may be that I did not treat the cut end properly, if at all - I confess, I forget. When I put in some fence posts, I did stand each for a few days in Creocote. However, I was a little sceptical as tohow far the liquid could have penetrated.

Many years ago, my father was visiting an old friend who was a woodwork teacher. When discussing rot, he told my Dad that rot, both wet and dry, occur at 12% moisture. Wood in the ground is generally above this value and does not rot. The top of posts are below this value and will not rot. "Wooden posts will always rot about 6" above the soil." was his pronouncement.

One gardening programme dug out trenches, laid a weed membrane over the soil but dropped a whole decking frame into the slots. Even with end-grain treatment, I wonder about the life of such a deck.

Also, would screws offer a way in for water to track? Of course, screws are tight, by water molecules are not exactly huge.
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Tanalised Timber Rotting

Post by arco_iris »

aeromech3 wrote:
Sat Dec 19, 2020 1:23 pm
there is a limit to how far the preservative seeps into the wood, when yours dries out, yes when, you need to treat it. One product for this is Ronseal wet rot wood hardener.
Although I haven't used Ron's Hardener (SFix stock it) for this particular purpose, it's great for things like timber door sill ends in conjunction with epoxy filler.

OP should remove that triangular piece of decking, wait for the timber to dry as much as possible, then drill several 3mm holes into the wood, side, top & end. Treat with the hardener, which will set very quickly., this should stop the rot going any further.
headey
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Tanalised Timber Rotting

Post by headey »

wait for the timber to dry as much as possible, then drill several 3mm holes into the wood, side, top & end. Treat with the hardener,
I think I actually have some Ronseal hardener. No doubt I'll have to wait until spring.

Actually, this reminds me of finding some rot in the frame of the house and doing something similar with a commercial borax solution. I think we still have some. I'd used it on the inside of the house, so not outside bombarded by the weather. Might still be worth a try?
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Tanalised Timber Rotting

Post by big-all »

i personally would not bother with hardener it adds no strength will just add a very weak like a hair spray coating to stop decay falling appart just wasted money :dunno:
spend your time replacing new for rotten timber keeping damp away by clearing leaves/ earth/add ventilation
or do it properly with "off the ground "separation

as an aside thinking out loud and not an actual suggestion :lol:
stabilizing solution will add perhaps 0.1 to 0.2 to the structure yes in my opinion zero or near enough
but pu foaming glue may add 20- 50% back to the structure providing you have say 10mm holes in the top and enough timber/brick or other structure to stop flowing to far beyond the base off the timber to give support
now any timber or brick will need to be covered in plastic or polly bag if you want to remove
now i would tackle it at say 200-300mm lengths max over say 3 or 4 days with timber and brick removed the day before to allow crusting
always put a bolt or peg in the top hole to send the foam down
now use this stuff
https://www.toolstation.com/polyurethan ... 50g/p93568
but as i say not an actual long term solution :dunno:
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El carajillo
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Tanalised Timber Rotting

Post by El carajillo »

I have a similar problem with a base for a greenhouse. I used 200 X 75 on edge which I had cut to length and then pressure treated in a cylinder.
One end barely touching the soil has rotted considerably.
As water is used inthe treatment I do wonder if they maintain the concentration of chemicals or just keep topping up with water leaving a colour.
Dipped fence panels do not fair any better (although the timber is poor to start with )
Nothing quite like the old creosote/ tar oil. :welcomeuhm:
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