Viewing 40 posts - 1 through 40 (of 52 total)
  • Talk to me about how to make a concrete shed base please
  • stayhigh
    Full Member

    Morning All

    I’m going to be building a shed in our garden and have started work on the base for it. The shed will be 10×6 ft and have dug a base pit out that is slightly larger then this and about 6 inches deep. I have half filled this with rubble and plan to fill the top with concrete.

    As I understand it I need to put a wodden frame work around the area to be concreted to maintain shape etc, do I have to use any particular type of wood for this or is anything ok and does this frame work get removed after the concrete has set?

    I also recall somebody saying that you should make the base smaller then the floor of the shed to allow for drainage or something along those lines. If so two of the walls to the shed are close to existing walls in the garden so would it be ok to leave these “gaps” or better to fill them in with gravel or something similar ?

    Sorry if this is a bunch of daft or obvious questions and your advice is much appreciated 🙂

    Stoner
    Free Member

    you can use any wood for shuttering but stuff with minimum texture and a good slathering of mould release liquid is a good idea for a nicer finish.

    If the hardcore level is clear of the surrounding ground you might consider blinding with sand and putting a damp proof membrane down to prevent moisture coming up through the concrete but if you’re not bothered (or the h/c is below ground level) it will save you hassle and money without it.

    stayhigh
    Full Member

    The rubble is below the ground level and when the garden is finished the ground will come upto the edge of the base. Would you say a damp membrane was non essential as I’m trying to keep things simple?

    Also what does “blinding with sand” mean, is that putting sand around the edge of the rubble/concrete base?

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    uwe-r
    Free Member

    The wood needs to be level or the concrete will not form the shape you are after!

    Get a spirit level on it!

    Stoner
    Free Member

    The wood needs to be level or the concrete will not form the shape you are after!

    pffft. Make a wet mix and let god be your spirit level 😉

    Stoner
    Free Member

    DPM isnt essential on a shed base IMO but it might be considered good practice – you cant very well add one later 😉

    blinding is imply putting a few inches of builders sand on the hardcore to get rid of the edges and voids that might puncture the DPM and give the concrete/DPM sandwich a smoother surface to sit on.

    If the DPM is below ground level though it’s not going to do a lot as moiisture can simply get into the concrete slab from the sides or through the blinding layer.

    stayhigh
    Full Member

    I’ve already been out and brought one in a rare moment of forethought lol

    With the size of the base is it best to divide it into say three sections and concrete each one seperately or would you just do the whole thing at once?

    The reason I ask is I’ll be mixing the concrete by hand as we have no way of getting a mixer out the back.

    So in this case its probably not worth putting a DPM down. Would there still be any point in putting a lyer of sand over the rubble in that case?

    crashdummy
    Free Member

    For a shed base any wood will do. As Stoner says smoother wood will result in a better finis but if it will be below ground that isn’t important.

    What you do want to make sure of is that the base is square (measure the diagnals as weel as sides) and level (form the wooden box to the level you want – not higher – and get a spirit level to check everything is level, then simply level off the concrete with a plank).

    Stoner
    Free Member

    to save hassle Id get one of those “Trumix”* co’s in. You can barrow it through from the front and you only buy what you need (no balance loads lying around being messy). But its quite a bit more expensive (IIRC about £80-90/cubic metre compared to £60-70 for just a mixer load)

    * ask for recommendations in your LBuilderShop

    Much faster.

    Stoner
    Free Member

    dont bother with blinding if no DPM

    uwe-r
    Free Member

    Ummm it’s nice to have a good tidy box to start with.

    Stoner
    Free Member

    then simply level off the concrete with a plank.

    easiest if it’s >6′ obviously – then you and a mate can tamp it back along the box top from one end to the other. For added poshness you can use a trowel to smooth a permiter band all the way round.

    stayhigh
    Full Member

    The idea of not having to mix it myself is nice but the only way I could get it out the back would be in buckets.

    I had thought about doing it in sections to make the tamping down easier as two of the walls will be close to two existing walls in the garden.

    Also should I make it smaller as previously advised (not here) or just go with the size of then shed?

    Stoner
    Free Member

    Also should I make it smaller as previously advised (not here) or just go with the size of then shed?

    I think theyre referring to rain water/shed wall run off landing on the slab and pooling under the shed – probably rotting the floor joists. If you are putting a kit shed with a wooden floor on the base then Id aim to overhang the base so that water can run down the shed walls and soak away through the ground/gravel around the base.

    If you’re building on top of the base with a “custom” made shed with no floor then Id think about how you get run off away from the wall bottoms.

    tonyplym
    Free Member

    Stoner suggested making the mix very wet so that it’ll flow and find its own level. Nice idea, but too much water will make any concrete mix lose much of its hardened strength and you’ll also find it tricky to get a good and impermeable (durable) top surface on the slab because all of the excess water will segregate to the surface. Much better to use a proper plasticising admixture if you can get hold of it – something like this would do the trick nicely. You don’t need much – 1% by weight of cement in the mix is typical.

    Most ready mix concrete suppliers would include a plasticiser like this in their mix recipe if you told them that you were using the concrete to pour a slab.

    Holyzeus
    Free Member

    Don’t bother with the blinding. Having the base slightly smaller isn’t a bad idea,
    It’ll help keep the water away from under the shed.
    Something i would think about is keeping the wood of the shed
    that is in contact with the base dry. Something like 4″ Dpc

    stayhigh
    Full Member

    Whats a DPC?

    Stoner
    Free Member

    DPC is the roll of black damp proof course (thick rubbery plastic sheet, 4″ wide to you). Not expensive, you roll it ou over the finished slab and sit the floor joists on it. Prevents the joists absorbing moisture/sitting in water and so rotting.

    Stoner
    Free Member

    Stoner suggested making the mix very wet so that it’ll flow and find its own level

    It doesnt need to be that wet to level with a bit of help with a rake and a board. But tamping along a shutter is the most reliable method.

    FunkyDunc
    Free Member

    Before putting concrete in think what security you want to put in the shed. The quickest and easiest solution for security that I could think of was a D Lock sunk in to the concrete so that the ends of the U shape would come up about 2″ inside the shed floor to which chains/cables can be connected to.

    spooky_b329
    Full Member

    Planning to handmix it? Have you ever tried mixing by hand? Even a couple of barrow loads is a good workout.

    Can you really not get one of these through the house?

    I’d rather spend two hours getting this into the garden than handmixing. A quick online calculator reckons you’d need close to 1.9 tons of concrete. Edit…based that on 6″ but you say you’ve half filled the hole with hardcore, so call it 1 ton.

    You could also consider pumping it…there is a one man band sort of outfit near me that has a van and a concrete pump on a trailer…sling the hose over the fence and just be ready with the rake as the concrete pours in 🙂

    TheBrick
    Free Member

    mixers like that can be taken apart and though doorways easily.

    Stoner
    Free Member

    if you’re in Worcs, you can borrow mine.

    EDIT – how are you getting the ballast through to the garden? by bucket?

    I pity you 😉

    noteeth
    Free Member

    “The Youth gets together the materials to build a bridge to the moon, or perchance a palace or temple on earth, but alas, at length, the middle aged man concludes to build a wood shed with the materials.”

    – Henry David Thoreau

    Stoner
    Free Member

    “If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations* under them. “

    – Henry David Thoreau

    * or concrete slabs.

    noteeth
    Free Member

    😀

    stayhigh
    Full Member

    We had the bathroom roof replaced last year and had about 200 concrete tiles leftover from that. I’ve used them for the rubble along with another concrete slab that was in the garden that I had to break up for Mrs Stayhighs garden plans.

    Our back garden is walled on 2 sides and fenced on another, behind our house is train line on a bridge so no rear access or any way of getting it out the back.

    I guess I could maybe hire a mixer and then bucket it through the house?

    How much concrete I’ll need was going to be one of my next questions after hunting through my trusty Collins Complete DIY 😉

    PS nice quotes 🙂

    brassneck
    Full Member

    let god be your spirit level

    That is now my maxim for life. Top work.

    FunkyDunc
    Free Member

    If you have to get everything through the house, how the hell are you going to get the shed through the house???

    Stoner
    Free Member

    We had the bathroom roof replaced last year and had about 200 concrete tiles …

    that’s your hardcore.

    Ballast is the pebble/sand mix that goes into your concrete mix with cement and water.

    100mm x 3050mm x 1850mm = 0.56m3

    Which is 8x 25Kg cement bags and a tonne of ballast.
    http://www.source4me.co.uk/calculate_concrete_mix.php

    -m-
    Free Member

    I guess I could maybe hire a mixer and then bucket it through the house?

    Given that the easiest thing to get to your back garden is water (assumin gyou have a hose) it would probably be marginally easier to carry the dry materials through the house along with a mixer and mixing it in the back – that way you save carrying the weight of the water, and aren’t carrying buckets of wet concrete through the house (in my case that would be a recipe for certain disaster)…

    Might be worth seeing if you can track down a wheelbarrow (or even a sack trolley if you’re using bagged materials) that fits through a doorway to make the whole thing easier.

    =0.56m3

    = about 50 buckets

    stayhigh
    Full Member

    Hmmm, thats a lot of buckets 😯

    I’ll have to do some measuring of doorframes and go and see what local hire places have to offer. Failing that theres gonna be a whole lotta humping going on 😉

    Cougar
    Full Member

    let god be your spirit level

    Don’t be daft. I’ve seem drawings and models, he couldn’t even get a simple wooden cross level.

    stayhigh
    Full Member

    Would this be ok for the ballast, it says minimun content 850kg.

    Is ballast all much of a muchness?

    Thanks for your patience with all my questions 🙂

    BTW I measured my door frames etc and could get something no more then 70 cm through.

    Stoner
    Free Member

    Why don’t you just lay some concrete paving slabs on some sharp sand on top of you hardcore. Got to be easier than buckets of ballast.

    You dont even have to cover the whole area, just sufficiently support the floor joists.

    stayhigh
    Full Member

    I must admit I hadnt even thought of paving slabs. Would it be a case of fill frame work with sand and then lay slabs on top? The when the garden was finished off the ground would come upto the framework and hold everything in place?

    Smarty
    Free Member

    +1 for flagging it. Not as perminent as concrete, should you ever decide to move the shed it’ll be real easy to put the area back to garden.

    Smarty
    Free Member

    Even easier, gravel it. Shutter it up with tanalised timbers fill it in with gravel, whacker it down firm, staple DPC to the bottom of some 3×2 tanalised and sit the shed base on the tanalised timbers.

    thekingisdead
    Free Member

    2nd the slab option (especially if you cant get a mixer in the garden. I did a 4′ x 6′ base and there is no way i’d consider mixing by hand!

    stayhigh
    Full Member

    On the face of it that does seem like a much more straight forward option and much less faff then concreting.

    How much sharp sand would I need, would that still be around a tonne?

Viewing 40 posts - 1 through 40 (of 52 total)

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