Concrete base for shed....how to...

Concrete base for shed....how to...

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Steve Campbell

Original Poster:

2,110 posts

167 months

Monday 28th July 2014
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I've binned my old 6*4 garden shed for a new 8*8 "log cabin" ... so I need to extend the concrete base (it's ~45cms longer & 1.4m wider to accommodate new cabin + a slight change of position) .. not a huge area to concrete ... so doing it myself...first time to "play" with concrete. Cabin is just that, no heavy traffic...just everyday garden use.

I've dug out and "shuttered" (19mm * 100mm boards) into 3 sections, making sure they are level, and dug out and leveled the bottom of each section.

My neighbor has an electric cement mixer I can borrow...and I have the time next weekend. I'd like to limit the amount of concrete to "enough" to ease my back and I also think 100mm of concrete is OTT for effectively a "pretty" garden shed. Looking forward to giving it a go and extending my DIY skills :-).

Was planning to use this stuff to both "line" the base and make the concrete.
http://www.wickes.co.uk/Wickes-Ballast-Major-Bag/p...
Questions :
1) How much "dry" ballast and how much concrete to fill the 100mm depth ? 25mm ballast / 75mm concrete ? 50/50 ? What would you do and why ? Less concrete = less work...but I want the base to be sound and last. If it's 100mm concrete...so be it.
2) If I use the above material, what proportions for the concrete ? 1 cement to 5 of these ? Anyone used this Wickes material for concrete ?
3) Any tips / pointers or "obvious" pitfalls in doing the job ? Have done some internet research but some pointers for a complete novice at this from the professionals would be good.

Thanks in advance !! Hope my back stands up to it.... my day job is desk bound most of the time :-)
Steve

TA14

12,722 posts

257 months

Monday 28th July 2014
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Is the ground clayey or sandy?

Steve Campbell

Original Poster:

2,110 posts

167 months

Monday 28th July 2014
quotequote all
Clayey....been heavy digging...even for 100mm :-)

TA14

12,722 posts

257 months

Monday 28th July 2014
quotequote all
OK so you don't need any visqueen.

What's the area that you need to concrete? If 5m2 that's 0.5m3 at 100mm depth which is 1200kg. IIRC 7:1 ballast to cement should be OK so that's 150kg cement (6 bags) and 1050kg of ballast (42 sacks) plus a few spare to make sure that you don't run out. That would be a lot of trips in the car for me. My local builders merchant will deliver for free which would mean one jumbo bag (=34 sacks) and ten sacks extra on top plus the cement. The ballast should be saturated but surface dry (SSD) don't add too much water and remember that compaction is vital for good strength. Oh and don't forget a tamping board.

B17NNS

18,506 posts

246 months

Monday 28th July 2014
quotequote all
Just do it all in concrete. I can't see any logic in laying some unmixed ballast and then concrete on top. You've got to buy it and move it anyway. Chuck a shovel of portland in with it and give it a mix prior - stronger base.

4" is fine for a shed base. I do 6:1 but every man and his dog has an opinion and does it differently. Wickes stuff is fine for bits but tend to be expensive for delivery. Check the merchants for costs on a bulk bag.

TA14

12,722 posts

257 months

Monday 28th July 2014
quotequote all
B17NNS said:
Just do it all in concrete. I can't see any logic in laying some unmixed ballast and then concrete on top. You've got to buy it and move it anyway. Chuck a shovel of portland in with it and give it a mix prior - stronger base.
Absolutely. My quantities above were for this. Upon reading the OP again it would be a disaster to lay unmixed ballast. FWIW I'd try ready mix companies unless your shed is at the end of a very long garden.

C Lee Farquar

4,066 posts

215 months

Monday 28th July 2014
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We would charge @ £180 inc. VAT for half a metre of ready mix, North Oxon, to give you a comparison.

Steve Campbell

Original Poster:

2,110 posts

167 months

Tuesday 29th July 2014
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There is already a 7' * 5' slab so I'm just extending it...& I thought 0.5m3 was minimum order which would be too much?

Thanks for comments...keep them coming !

[

Edited by Steve Campbell on Tuesday 29th July 07:46

myvision

1,931 posts

135 months

Tuesday 29th July 2014
quotequote all
C Lee Farquar said:
We would charge @ £180 inc. VAT for half a metre of ready mix, North Oxon, to give you a comparison.
Holy st have you put gold fibres in that?

C Lee Farquar

4,066 posts

215 months

Tuesday 29th July 2014
quotequote all
It gets cheaper per metre the more you have, at smaller quantities the price of the concrete is almost irrelevant compared to the overheads of running the business and trucks.

The concrete element is only £40.85 plus VAT on half a metre, but it doesn't advertise itself, book itself in, invoice itself, insure itself, deliver itself, Bank the payment or wash the truck out, etc.

You get the jist.

Steve Campbell

Original Poster:

2,110 posts

167 months

Tuesday 29th July 2014
quotequote all
Exactly why I'm going DIY as by my calculations at a 6:1 mix I need about 18 bags of ballast + 3 of cement...total cost < £50

OK it'll take more time, but it's something I've not done before so actually looking forward to giving it a go....and even if I make a bit of a hash of it, it's only for a garden shed and I'll do the back bit first so you can't see it :-)

tleefox

1,110 posts

147 months

Tuesday 29th July 2014
quotequote all
C Lee Farquar said:
We would charge @ £180 inc. VAT for half a metre of ready mix, North Oxon, to give you a comparison.
Is there a part load charge in that?

C Lee Farquar

4,066 posts

215 months

Tuesday 29th July 2014
quotequote all
We price on a fixed delivery charge plus the concrete, nearly everyone else charges part load per metre not delivered. Being a small independent we don't have our own quarries or cement manufacturing facility so we don't make much adding value to the raw materials. In our case we need to make pretty much the same amount whether delivering 0.5 metres or 4 cubic metres. We're still cheaper than the firms with 6 & 8 metre trucks but more that the volumetric mix on site.

anonymous-user

53 months

Tuesday 29th July 2014
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myvision said:
C Lee Farquar said:
We would charge @ £180 inc. VAT for half a metre of ready mix, North Oxon, to give you a comparison.
Holy st have you put gold fibres in that?
Fooook me yikes an excolleague at independent was quoting me £120 a metre, 10 mil 325c/c air entrained with fibres for my drive last month and I told him he was robbing me biglaugh.

I take it your on "mixers" as there seems to be moves afoot or rumblings of removing the "plant" status and the "associated benefits" of volumetrics

http://www.cyclingweekly.co.uk/news/latest-news/da...
http://transportoperator.co.uk/2014/03/03/volumetr...

Let's just say the "mixer" boys are 'smiling' smile

C Lee Farquar

4,066 posts

215 months

Wednesday 30th July 2014
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speedyguy said:
Fooook me yikes an excolleague at independent was quoting me £120 a metre, 10 mil 325c/c air entrained with fibres for my drive last month and I told him he was robbing me biglaugh.
In North Oxon you'd be looking at close to £100 a metre plus VAT for that mix for a full load, pretty much a standard pattern driveway mix. So if your quote was including VAT it wouldn't be too far off.

We run small mixers and would be pleased if the volumetrics came under normal HGV drivers hours and constraints.

It seems ridiculous that we have restricted hours of operation on our Operators Licence yet if I added a volumetric, that would be double the weight, I could run it 24/7 from the same site.

myvision

1,931 posts

135 months

Wednesday 30th July 2014
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We had a major fk up yesterday and ending up dumping 65m3 where do you live op?

TA14

12,722 posts

257 months

Wednesday 30th July 2014
quotequote all
Steve Campbell said:
Exactly why I'm going DIY as by my calculations at a 6:1 mix I need about 18 bags of ballast + 3 of cement...total cost < £50
One of us has misunderstood the problem here. I get (1.4 x 2.45) + (1.5 x 0.45) = 4.105m2 meaning 0.41m3 or 984kg which is 40 sacks, about double your estimate.

Steve Campbell

Original Poster:

2,110 posts

167 months

Wednesday 30th July 2014
quotequote all
TA14.....would be good if you can check my calcs then.

Original size was what I "thought" it was (typing from work)...I've now measured accurately and the area needed filling is 3.7m2...so at 100mm that would be a max of 0.37m3. The Wickes web site says each ballast bag will give 0.35m2 at 50mm depth for course concrete...so by those numbers..I reckon a max 21 bags ballast (+ concrete at 6:1 ratio). Is my man maths right ?

I'm in South Bucks


Edited by Steve Campbell on Wednesday 30th July 09:39

TA14

12,722 posts

257 months

Wednesday 30th July 2014
quotequote all
3.63m2 at 100mm deep is .363m3. Concrete has a nominal density of 2400kg/m3 so that's 872kg for your project. Plus waste it's probably 1,000kg but call it 900kg, that's 36 sack's, less two to allow for the water if you like but certainly a lot more than 21.

(FWIW, I would just lay flags.)