Concrete Base For Garage

[iamlee2002]

Hi all, im planning on building a garage down the bottem of my garden. I have removed all the rubbish that was down there ready to start. My question is with the base, Can i just pack the clay down then use dpm and fill with concrete? or must i use sand / ballast ontop of the clay? The clay is pretty solid down there, ive hit it with a pick axe and it just bounces off. I wont be parking the car in there as its mainly for storage. Also what works out the cheapest, Ready mixed or mix myself? if its only a few £ for ready mixed then id have this. Thanks in advance all. Advice is greatly appreciated.

Lee

 

[RedHerring2]

A typical concrete floor won't last long on just clay. Clay will shrink in dry weather and heave (expand) in wet weather.
You ought to dig out sufficient for 150mm well compacted hardcore, then a reinforced 100 - 150mm concrete on top. (I would suggect 150mm for a garage)
If you want to install a dpm add 50mm sand on top of hardcore before dpm.

What size are you thinking of?
With what materials were you intending to build?

 

[wavetrain]

The clay is pretty solid down there, ive hit it with a pick axe and it just bounces off.

Greetings to our friends north of the border


I have seen brown clay
and also blue clay
but I have not so far seen rubber clay.

Or is your pick axe made of rubber?

 

[mointainwalker]

"...Greetings to our friends north of the border .."

Well, that would be west of the border really, or is your map a bit dodgy ?

 

[wavetrain]

"...Greetings to our friends north of the border .."

Well, that would be west of the border really, or is your map a bit dodgy ?

It's the thought that counts when it comes to geography

 

[RedHerring2]

"...Greetings to our friends north of the border .."

Well, that would be west of the border really, or is your map a bit dodgy ?

It's the thought that counts when it comes to geography

Tell that to Colombus. He thought America was India.

 

[iamlee2002]

hi all thanks for the advice ok i will dig further down to put hardcore, then use wacker plate and finally concrete it. Im debating whether to mix the concrete myself or get ready mixed in. The area is 20 sq mtrs

 

[foxhole]

Ready mixed then you have a continuous slab rather than a patchwork as you may not be able to mix it quick enough.

 

[RedHerring2]

Ditto, the ReadyMix.
Assuming you're doing 100mm thick, 2m³ can be mixed on site by a couple of healthy lads, assuming you have all the matrerials close by and the distance to the base is minimal. But it's still a good days work.
If you're doing 150mm thick that's 3m³ and you might struggle to complete that in one day, unless you have two mixers going and some extra labour.

Think carefully about the access and the distance to be carried for the readymix. It might be worth you considering a pump. A pump may cost you about £150 but it comes with two guys who, more or less do all the work. You just have to tamp and level.

Cost wise, there's little difference in mix on-site and readymix, when you consider all the work that goes into mix on-site.

Incidentally, there's little point in installing a dpm in a stand-alone garage that has no insulation or heating 'cos you'll still get condensation on cold surfaces, e.g floors. windows, walls, etc.

 

[iamlee2002]

Hi again, Ready mixed its going to be then . I live on end of terrace with side entrance so the ready mixed lorry can reverse in. I think im best to go for 6 Inch as 4 inch might be a bit to weak if ever i wanted to park car in. Ill have to start digging out the clay soon not sure whether to hire a mini digger because clay doesnt budge with my spade. At the moment ive gone down 4 inches with 6 inches of concrete i will be about 2 inches above outside ground. How much hardcore do you recomment i use? and what type? I will install dpm just to be on safe side to stop rising damp, Thanks in advance

Lee

 

[RedHerring2]

150mm well compacted MOT Type 1. So about 3m³ is about 5 or 6 Jumbo Bags. Or if you can buy it by the tonne and tip it straight in, so much the better and cheaper. I'd guess about 4 or 5 tonnes. You should be able to find a calculator on the 'net or guidance on this site by searching.

Don't forget the mesh in the concrete.

I would still suggest that you reconsider the dpm. I found that my garage, even with insulation and dpm in the floor, suffered condensation before the rendering was completed. This was due to damp coming through the single skin concrete block walls. So I would reiterate, re-consider your dpm, unless you intend to install some insulation, heating or ventilation, and you intend to keep damp out of the remainder of the garage structure.

Having said that, I installed underfloor insulation (and over-rafter insulation) as future-proofing, rather than a requirement now.

Incidentally, you'll need to excavate about 250mm (10") for 150mm of hardcore and 100mm of concrete below ground and 50mm of concrete above ground, I assume using 3X2's as former just laid on the ground and staked or similar. Don't underestimate the power of concrete to exert a horizontal force.Add another 50mm to that if you are going to use dpm (for sand blinding)

I think it was 'theoldun' who did an excellent calculation of spoil to be disposed of. It will gice you some idea of how much needs to be dug out.

 

[RedHerring2]

Found it, thanks again to theoldun:

The bulking factor for excavation varies in relation to the material being excavated. Examples.
Chalk 1.6. Clay 1.2. Stiff clay 1.5 Top soil 1.25 Gravel 1.1. Rock 1.5 Sand 1.05.
When estimating we always factor 1.4 for ground that we do not know the make up of, therefore 6m3 in the solid is 8.4m3 in the loose
8 cube yard skip equals 6m3, so two number 8 yard skips will suffice. In the UK we would budget for £180.00 plus VAT per skip. Your skip price is very cheap for 8 yarder.
A 6 wheel grab lorry will also lift and cart 12m3. Once again in the UK we would budget for a 6 wheel grab at £190,00 plus VAT.
As you can see grab lorry is half price of two skips.
If you do go for grab lorry, remember they have to stand sideways on to spoil heap to load.
oldun.

So, using a bulking factor of 1.5. You have already removed 100mm and you have a further 150mm to go. I make that about 3m³ before the bulking factor so you have a further 4.5m³ to think about digging.
2 or 3 days hard work, or ½ a day with a digger?

There's no reason why you couldn't just have the hardcore in the ground and all the concrete above ground. You'll just need to shutter it carefully.

 

[iamlee2002]

thanks buddy very useful info Will post later on when i get somewhere with project. Going to hire mini digger just trying to get the best price near me lol