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oak or softwood sleepers

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skeetstar

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Hiya, my daughter is doing some landscaping work, and she is looking to get rid of an 18in high retaining wall and replace it with sleepers.
She asked me whether they should go for Oak or softwood. The softwood is 'treated' and I guess the Oak is or could be given a coat of preservative.

Her question to me ... is it worth paying £580 for the oak as opposed to £230 for the equivalent number in softwood. I'd lean towards the Oak, but then would it last twice as long as the softwood, when used as a retaining wall for soil?

If Oak is the answer, then what might be a good preservative?

Grateful for some guidance from those who know better than me,

Thanks all.
 

Woody2Shoes

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I'd use masonry. All timber in contact with the soil will rot - the only question being how long that takes (and the answer will depend very much on local conditions).
 

robgul

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I'd use masonry. All timber in contact with the soil will rot - the only question being how long that takes (and the answer will depend very much on local conditions).
100% agree that blockwork with either render or thin timber cladding will last a lot, lot longer. Previous house we had raised beds with oak sleeper-sized boards - they were "treated" but still rotted badly within about 5 years (replaced with blockwork)

BUT to answer the original question, go for the cheaper softwood and make sure you line the soil-facing side with thick polythene membrane (and even 2 thicknesses of it, with the top somehow fixed to stop water getting between it and the timber. I've not used them but I'm told that ex-railway sleepers last pretty well as they are impregnated with a tar-like substance - downside is that they look a bit rustic and you can't sit on them as they'll mark clothing.
 

Spectric

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The softwood could rot out in two years depending upon conditions, hardwood like oak will last many years providing they are not burried in the ground, some say at least 10.
 

Sgian Dubh

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... hardwood like oak will last many years providing they are not burried in the ground, some say at least 10.
European oak is classed as durable, meaning 15 - 25 years of life in contact with the ground. Durability of this sort of length is one historical reason in this part of the world (Europe) for oak being a favourite on which to hang agricultural and other gates, whether the gates themselves were made of wood or steel, or anything else I suppose.

On the other hand, even longer life expectancy for a soil retaining wall would be brick, stone, blockwork, and so on, or possibly heavy duty composite plastic board material, e.g., something like these, or at a lesser price, these. As to the aesthetic qualities of these different options, that's not something for me to make a comment. Slainte.
 

TheTiddles

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I had a similar height retaining wall, made from treated “sleepers” as was the rest of the garden, lined where soil touched them, ends dunked in preservative... rotten in a couple of years.

Replaced with concrete, no signs of rot yet.

If they don’t like the look of masonry, I’d design that problem away, rather than create another more fundamental one. But masonry will likely be more than the oak if you have to get someone in to do it
 

Jacob

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Big fashion for timber garden retaining walls etc was based on the availability of old railway sleepers and/or old reclaimed joists/beams which were dirt cheap because worthless except for firewood. Buying new stuff is slightly bonkers!
Get a price for dry stone walling or something? Much nicer anyway, compared to a creosote soaked piece of scrap wood - preservatives are toxic to plants and the environment too.
 
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AJB Temple

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If there is already a functioning masonry retaining wall, that could be rendered or painted if necessary, replacing it with sleepers or new wood of any kind is surely a backwards step? Spend the money on plants.
 

MARK.B.

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If your daughter is set on having sleepers then you could use old railway sleepers as the bottom layer in contact with the ground as they will have a much longer lifespan than the newer ones you could use for the rest of the wall :)
 

robgul

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Not yet mentioned is a wall constructed with gabions (wire box filled with stones) - at only 18" high it would look great and be very durable. I don't think it's quite as simple as just pouring the stones in but it can't be that complex.
 

skeetstar

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Folks thanks for all the input, it is much appreciated,
I've passed it all on to her, and as its her money, I@ll leave her to make up her mind.
Thanks for the thought about Gabions Rob.. I'm going to explore that.
 

TheUnicorn

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depending on the condition of the existing wall, I'd consider attaching vertical battens (for air flow) then horizontal cladding
 

mossycave

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Folks thanks for all the input, it is much appreciated,
I've passed it all on to her, and as its her money, I@ll leave her to make up her mind.
Thanks for the thought about Gabions Rob.. I'm going to explore that.
i built an 8m gabion wall about 1m high as a retainer. Works great for that function. I should have gone for thicker gauge wire and used more bracing wire as there is some minor bowing, but at 18” high I wouldn’t think it’s a problem. I’m just finishing some timber tops for them because the kids have climbed all over them and bent the mesh.
 

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ade_tumu

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One additional consideration if you go down the sleepers route: not all sleepers have the same level of treatment / protection, even if they say 'treated'. The key would be get sleepers that have been treated to Use Class 4 ("UC4"), which is for outside use in contact with soil. This would give a claimed life expectancy of 15 years. Many sleepers are treated to a lower standard of Use Class 3, and would rot much quicker.
 

Jacob

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A simpler variation on the gabion idea is to put up shuttering for the face of the wall and build up to it carefully so that when you take the formwork away you have a very neat wall with one flush face. Shuttering can be ply or boards such as old floor boards, with posts to keep them in place.
 

jcassidy

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I've seen concrete cast against heavily grain wood shuttering, leaving the grain of the wood on the concrete.

I think replacing an existing solid retaining wall with wooden sleepers is not a great idea. Beautify the wall with cladding would surely be cheaper, easier, and longer lasting.
 

Woody2Shoes

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I've seen concrete cast against heavily grain wood shuttering, leaving the grain of the wood on the concrete.

I think replacing an existing solid retaining wall with wooden sleepers is not a great idea. Beautify the wall with cladding would surely be cheaper, easier, and longer lasting.
I like this 'best of both worlds' idea - concrete retaining wall (with steel re-inforcement) and timber cladding. Relatively inexpensive and very longlasting.

A friend made 'gabions' out of treated sawn 4X2 (on a steeply sloping site) - he sold the place promptly and I dread to imagine what the new owner took on!

Even with galvanised steel cages, I think that gabions are a hostage to fortune (my instinct would be to pour a load of strong cementitious grout in on top....) - steel rots in the ground too.
 

Jacob

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Forgot to add - chap next door built raised beds all over his garden about 8 years ago.
Were treated but all rotted - he gave them to me for firewood. Burns nicely once its dry which doesn't take long with old wood; "wet" isn't the same as "unseasoned"
 

converse

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This can be a great and attractive way to recycle a redundant concrete slab - have a look at "Urbanite" retaining walls. Basically chunks of concrete laid as dry stone wall.
 
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