Viewing 18 posts - 1 through 18 (of 18 total)
  • My wall building dilema
  • llama
    Full Member

    This summer's patio in the garden project is ramping up and this weekend I want to build a retaining wall

    It is to be about 80cm high and a good 15m long, walling off 3 sides of a patio (to follow after the wall). Its going to be made from concrete blocks (later rendered and painted).

    Unfortunately I have a dilema as Mrs Llama has enlisted her Dad to help. Now he knows a bit, being a retired surveyor and son of bricklayer. But I'm not sure what he is suggesting will be up to it.

    His plan is as follows:

    Dig trench to depth equal to the width of a block (i.e. 3 inches) plus 'a bit more' and lay a level foundation using blocks on their side bedded in alot of mortar. Then wait for this to go off. Then build the wall up on the foundation – 3 rows of 1 block wide.

    The 2 things that worry me about it are (1) are the foundations deep enough and (2) is a 3 inch wall enough to retain 80 cm of earth. 'Cos I've looked around on the 'net about this and from what I see it would be propper to use concrete foundations of 1 foot and a wall of at leat 9 inches wide.

    He just says: yes foundations are deep enough, Victorians never bothered with them etc etc; and yes 3 inches is wide enough because the soil is pretty solid and unmoving. The last bit does seem to be true as another bit of the garden has 1.2m high held back by a thid reinforced concrete coal bunker until I removed it >1 year ago and it has not budged.

    So …

    Will it work?

    Or Should I overrule him and tell him we are doing it my way?

    And if so then how to let him down gently because I don't fancy doing the whole thing by myself.

    fenboy
    Full Member

    100mm thick foundation should be fine, make it 150 if you are worried 400mm wide then lay the blocks on the flat so it comes out at 215 thick (9") then its going nowhere!

    aP
    Free Member

    I wouldn't be very keen, but then apparently I'm very risk averse.

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    rusty-trowel
    Free Member

    Yep, at LEAST 215mm wide, and definetely on a concrete foundation. Couldn't be more precise without seeing it, but with retaining walls, go on the side of caution. Alternatively, pay me loads and i'll do it. (p.s. surely blocks are 4" not 3"?)

    STATO
    Free Member

    if its only getting a patio on top and dosnt have any weight behind it (ie. not stopping a garden sliding down a hill) then itll prob be fine.

    Olly
    Free Member

    we were doing an excavation next to a house last week, and it turns out it had NO foundations.
    none
    zip

    listed 300 yr old 2 story cottage build DIRECTLY onto the topsoil.

    RE the OP: not a clue.

    psling
    Free Member

    Like said above, the bosse's father is suggesting 215mm thick (block on side) which is pretty wide. If it is retaining earth, ground, whatever then my advice is drainage. You must allow drainage through the retaining wall.

    llama
    Full Member

    yes he is saying a foundation of flat blocks so 100mm deep and 215mm wide, then a wall of 3 rows of 100mm wide blocks

    what troubles me is that 300 year old cottages tend to be made from something a bit more substantial than concrete blocks 🙂

    tim41
    Free Member

    Do you mean 3 courses of 100mm wide blocks over 1 course laid flat?
    If so, i'd say not a chance, although i'm quite risk averse too.
    The soil behind may be 'pretty solid' but bear in mind you'll have to back fill behind the wall with 'pretty loose' soil.
    You'll definitely need a concrete base and minimum 215 thick blockwork, probably thicker at the lower part. And weep holes.

    rusty-trowel
    Free Member

    This thread has the potential to turn into a stw builders ride. This would lead to a carpark full of white vans, plenty of head (and bum) scratching, cups of tea a plenty, then ride like mad until dinner time before going down the pub for the rest of the day.

    llama
    Full Member

    much sucking of teeth

    tim41
    Free Member

    who said anything about builders 😯
    cue engineer jokes…

    llama
    Full Member

    Do you mean 3 courses of 100mm wide blocks over 1 course laid flat?

    Yes that is his plan

    On the above I am leaning towards 215mm thick (i.e. laid sideways instead of standing up) which would mean about 6 courses.

    What size foundations? Are blocks suitable as foundation or is concrete the way to go?

    aP
    Free Member

    I'm not a bloody engineer, but I do work with a lot of them – they keep talking about Spheroid Graphite Iron segments though which might not really be appropriate for this situation (or for that matter TBMs either)

    tim41
    Free Member

    I can't really say what size concrete foundation, too many unkown factors. Good site here for diy landscaping stuff. The wall at the bottom of the page shows brick but the same principles apply for concrete blocks.

    Sandwich
    Full Member

    Rusty, there's a lack of bacon rolls and big breakfasts in your description. I would go with 300mm wide by 300mm deep concrete footings for what you describe. My footings were slightly wider for a similar height but I skinned my wall in brick, using hollow blocks and the subsoil is ballast. It is a huge patio though.

    gazman
    Free Member

    150mm max thickness of concrete for foundation and 450mm wide with blocks laid on side with weep holes to allow water to run away also backfilled 150mm wide with limestone chippings to allow water to run through to weep holes, weep holes can be plastic pipe 32mm diam every 1m or so. the reason for getting water away is less weight behind wall. gaz

    stumpyjon
    Full Member

    Think Gaz has it pretty right. One question, is the wall stopping the surrounding soild from ending up on the patio or is the patio going to sat on top of the retaining wall. If the latter I'd definitely beef it up. I built a similar height retain wall along my patio. Foundation was a load of rubble with around 100mm of concrete on top an in around 350mm wide. I then built the wall double thickness, brick skim on the front, concrete block at the back. Filled the void between them with mortar. Then laid a big concrete slab against the footings for the patio. Hasn't showed any signs of shifting in five years.

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