Dom's workshop build

[DomD]

Don't fall into the trap of assuming depths of hardcore and blinding until you have actually dug a hole. It might be you don't need any hardcore, and if you don't, you'll only need a dusting of sand blinding.

Are there specific conditions under which I should be checking the ground conditions?

I have just got two quotes for 4m^2 of concrete and pumping and both are ~£1000 (incl. VAT). I spoke to a patio/driveway groundwork guy who said he would definitely suggest piers over pumped concrete; I'm going to look into the cost of this but would rather work of a solid concrete floor than a floating one.

Any pumping/concrete companies anyone recommends in the Watford area?

Thanks

 

[MikeG.]

Do you mean 4 cubic metres?

I definitely wouldn't pump that. I'd get a friend to help, and barrow it. You'll do 4 cubic metres in a morning that way. Or you could hire a mini dumper.

 

[DomD]

Do you mean 4 cubic metres?

I definitely wouldn't pump that. I'd get a friend to help, and barrow it. You'll do 4 cubic metres in a morning that way. Or you could hire a mini dumper.

It is ~4m^2 but my garden (which I think I posted an image earlier) is on a hill with a retaining wall and steps up to the main area so I would need to construct a ramp and it would be a lot of work up and down. A mini dumper definitely wouldn't get up.
I anticipate it will be enough of a pain to set up the form/subbase so want the concrete delivery to be as smooth with as little mess as possible.
- Dom

 

[AJB Temple]

The problem with pumping is it is uneconomic for small quantities as the pump lorry is a separate machine and another bloke. I would be very surprised if the hill is so steep that you can't get a 1 ton hydraulic dumper up it. That would save a lot of backbreaking work and would be cheap as you could pour from a standard delivery lorry.

 

[MikeG.]

16sq m x 0.15 (depth) = 2.5 cubic metres of concrete. Seriously, just with barrows, that's not much more than an hour or two of work. You'll have to pay a little extra for the mixer waiting on site longer than normal, but it's only going to be pennies compared with hiring a pump. Part load charge (or batch mixed), and you'll have the concrete done for around £300/ £350.

 

[DomD]

The problem with pumping is it is uneconomic for small quantities as the pump lorry is a separate machine and another bloke. I would be very surprised if the hill is so steep that you can't get a 1 ton hydraulic dumper up it. That would save a lot of backbreaking work and would be cheap as you could pour from a standard delivery lorry.

The problem isn't so much the hill but the retaining wall which would mean I would need to construct a ramp of sorts.

16sq m x 0.15 (depth) = 2.5 cubic metres of concrete. Seriously, just with barrows, that's not much more than an hour or two of work. You'll have to pay a little extra for the mixer waiting on site longer than normal, but it's only going to be pennies compared with hiring a pump. Part load charge (or batch mixed), and you'll have the concrete done for around £300/ £350.

It's actually gone up to 14*20ft so at 150mm that's 4m^3. I would need to make a ramp for the wheelbarrow and the hill is at least 35° in parts but I guess that could be possible, especially if I get some help. I will look into the cost of no pump: for the companies I quoted the breakdown was half for concrete half for pumping so my guess is ~£500.
Thanks

 

[TopCat 32]

if you go readymix route 4 cube about £90 a cube = £360 you may get a uncarried concrete charge of £37 on the 2m he is not carrying , ( you may get away with this you may not) best check, you will get 30 mins to unload the 4m3 after that it is about £120 a hour waiting time ( theses trucks cost 120 grand each now) so cant be sitting about waiting to discharge, as i tell groundworkers when i am waiting for trucks to return " you bought the concrete not the truck", make sure you have enough labour and wheelbarrows if you dont pump as you can tell it will get dear otherwise,
volumetric will not charge for uncarried concrete and will give you more waiting time, but we keep a check on there prices and last check a equivalent mix to ours was around £160 a m3, not sure how many meters you need to pump but a small trailer pump should cover this, Embassy pumps at caterham would come to you i'm sure, any help i can give please ask
good luck Dom
regards tim

 

[MikeG.]

if you go readymix route 4 cube about £90 a cube = £360 you may get a uncarried concrete charge of £37 on the 2m he is not carrying , ( you may get away with this you may not) best check, you will get 30 mins to unload the 4m3 after that it is about £120 a hour waiting time.........

Paying for half an hour extra on site time (they allow an hour around here, BTW) would on your figures amount to about £440 or £450 total, which compares quite well with £1000 quoted for concrete + pump.

 

[Junah]

Where are you based? might be able to get a working party together to wheel the barrows.

 

[DomD]

if you go readymix route 4 cube about £90 a cube = £360 you may get a uncarried concrete charge of £37 on the 2m he is not carrying , ( you may get away with this you may not) best check, you will get 30 mins to unload the 4m3 after that it is about £120 a hour waiting time.........

Paying for half an hour extra on site time (they allow an hour around here, BTW) would on your figures amount to about £440 or £450 total, which compares quite well with £1000 quoted for concrete + pump.

If I was to barrow it what sort of angle would be needed for a slope up the hill? Again, reposting back garden photo from earlier:

You can see in the lower part of the image there is the steep part with the stairs: my guess is this goes up at least three meters from the patio level before it levels out to a more manageable slope.
The other issue would be spillage which would definitely not happen with a pump.

According to this concrete supplier it will take about 25 trips/m^3 or 100 trips total and they recommend 1 person and barrow per m^3. This would mean buying (or hiring) 4 barrows and I doubt this estimate is intended for the distance I would be taking it.

The main reason I have become sceptical about the whole concrete base is that the groundwork contractor I spoke to was adamant that it was not a good idea and recommended a pier foundation: I think preparing the form-work/sub-base would be fine but getting concrete/hardcore up there is the challenge.

Where are you based? might be able to get a working party together to wheel the barrows.

I am in the Watford region but should be OK for helpers - benefits of having a large family to enlist.

Many thanks, Dom

 

[MikeG.]

Piers mean a suspended floor, with a gap underneath, putting your floor level likely 350mm or so above ground level. Not only is that 2 steps up, but it is normally enough to mean the whole scheme falls foul of the height restrictions imposed by permitted developments as you approach a boundary. That's the problem with listening to people who don't have an overview. What on earth does a groundwork contractor know about permitted development rights?

There is an alternative construction method given in my signature, which you might have a look at. The second one. Were you to go along that route I suggest reducing your spans somewhat, otherwise you'll have a sub-wall at mid-span.

 

[TopCat 32]

According to this concrete supplier it will take about 25 trips/m^3 or 100 trips total and they recommend 1 person and barrow per m^3. This would mean buying (or hiring) 4 barrows and I doubt this estimate is intended for the distance I would be taking it.

Dom , that is what we quote as well, you will be surprised how Knackering barrowing 4m is, not wanting to put you off but that it will be best part of 10 ton to move.
as for slope , yes you will get spillage and if wet a right pipper pushing barrows uphill even if you lay scaffold boards down 1st, not sure on the distance from truck discharge point to where you are laying slab, but i would think if you had 4 fit blokes on barrows, and a couple laying/ tamping, you may get it off in a hour to 1.5 hrs, we have had people try these track barrows, which hold about 5 conventional barrowes a time, cost of hire im not sure , but the speed they travel you cold do at least 3 trips with a normal barrow so they are not really cost effective, have you tried contacting a pumping firm for price of pump only . Like Mike says find out from supply companies what they allow you, if you can find one that will give you 1 hour to tip you will save, not sure who he uses , but my guess some of the small independents may be more accommodating, especially if work is quiet, i would go for a slab over pillars all day long

GOOD LUCK

 

[Echo-Star]

Hi Dom

Reading your thread i see you hav'nt set out foundation layout yet, this is easily done with a water lvl "garden hose* 4 x stakes and a string line, start at your highest point and work round, squaring your line as you go 8/10/12, this method works regardless of the lie of the land, I'd go for rectangle shape everytime over the L and a room inside a room is better, bigger is best. Also as you may have to remove 4/5 ton of top soil that has to go somewhere, then maybe use this to gentle the slope if taking the wheelbarrow option.

Rob

 

[MikeG.]

...... squaring your line as you go 8/10/12..........

?? That's not the pythagorus I know....... That'd produce a bit of head-scratching on site.

 

[Echo-Star]

is it not a case of scaling up 3/4/5

 

[MikeG.]

is it not a case of scaling up 3/4/5

No, not even close. 6/8/10 is, though. Or 9/12/15. Another useful pythagorean triple is 5/12/13, or multiples therefof.

 

[manglitter]

This may be useful then....

Sent from my SM-G960F using Tapatalk

 

[DomD]

Piers mean a suspended floor, with a gap underneath, putting your floor level likely 350mm or so above ground level. Not only is that 2 steps up, but it is normally enough to mean the whole scheme falls foul of the height restrictions imposed by permitted developments as you approach a boundary. That's the problem with listening to people who don't have an overview. What on earth does a groundwork contractor know about permitted development rights?

There is an alternative construction method given in my signature, which you might have a look at. The second one. Were you to go along that route I suggest reducing your spans somewhat, otherwise you'll have a sub-wall at mid-span.

Height isn't so much an issue as I am 2m from boundaries. Is there any threads with images of people who have tried your alternative design? If necessary I could reduce the span to 4m.
As I said I definitely hope to do a slab.

Unfortunately I can do very little on this until early June (other than planning). Is there an ideal time to check ground conditions to see how much sub base I would be looking at?

Thanks

 

[DomD]

After getting a quotes for the concrete slab and looking into the suspended option I think I will just do the slab myself with 150mm sub-base (or less hopefully) the sand and DPM then 150mm of concrete.

Any good resources on how to properly construct the wood form? I also want to keep the slab in line with my fence and another building so I suppose I will just measure at each end the length to the fence and keep it constant.

Is a perimeter of gravel around worth doing?
Thanks

Edit: Also looking at a mini dumper I think I may be able to take it up the stairs to the upper garden? If so this would help hugely and I could probably use it for both hardcore and concrete. They are also very affordable. Otherwise, is there a good way to make a ramp for a dumper? Scaffold boards layed over the stairs?
With a 0.5t mini tracked dumper it would be 20 trips for the concrete. My guess would be at least 10m a trip so up to 4h on site.

 

[DomD]

After a discussion with Mike this is the base structure I think I am going to go for:

EDIT: This is wrong, sub base should be under the edges, not in the middle.
There will also be A142 mesh throughout the top 150mm of the slab and the thickened edges will be slightly thinner.

Initially I was just going to do the 150mm with slightly thickened edges but the subsoil at the front of the plot extends down to 500mm below the surface as shown below:

So instead I am going for a 'raft-style' with subsoil and a layer of hardcore (with sand blinding) between the two edges. At points the thickened edges will be 500mm in depth.

I was concerned about 'clay heave' but luckily the soil in my area seems to be mainly silt/sand with very little clay; if there was clay I would have needed to add a void former which are quite expensive.

I think plugs in the floor would be very practical (if they can be kept flush/below the surface so I can still assemble stuff). I've seen people putting ducting through or below the concrete but am unsure of the best way to do this. Are there any specific products that would be suited to a concrete floor in a workshop?

Thanks, Dom