Concrete bases for concrete monstrosities.. I mean, garages.

[aaronjb]

Afternoon all ..

I'm (still) in the process of trying to arrange having a concrete sectional garage erected (after discovering I can't afford to have a brick built unless I suddenly win the lottery!) and.. well, either I worry too much, or..

One of the garage companies specifies the following for a base:

150mm CN30 concrete over total area with A252 reinforcing mesh over ~150mm of MOT1
300mm of the edges to be deeper (300mm) with two layers of A252

The base would be ~5.5m x 5.5m

I had a quote for laying such a slab and it came in (including knocking down the old garage and levelling the slightly sloping ground) at £4000 inc. VAT

So off I went to get more quotes..

Second quote is much more reasonable at £2500 but the concrete is mixed on-site (so it's not strength rated) and put in by barrow rather than arriving on a readymix truck..


Now the question is, should that concern me at all, really? Or is 'standard' concrete fine for a garage and the specs of the concrete garage company just a little overly enthusiastic?


I'm having that twitch again that says "Just do it yourself, then you'll know it's done right" - though having never worked with concrete and definitely never with steel mesh, I worry I'd just end up doing it wrong!

 

[studips]

all i'd say is that if you phone around for the cheapest supplier to meet the mix, then the materials plus labour to mix 5mcu of concrete with a mixer against ready mix makes ready mix the best option by a long way.

still, concrete is only part of the quote - demolition, waste removal, excavation, fresh type 1, shuttering and so forth being the rest.

you can work the quote out a bit for yourself -

5.5mcu concrete - £450 to £550 readymix
8 tonnes type 1 - £240 to £280
skips or muckaway £200 to £400
sundry items - timber for shuttering, digger hire say £350
the balance being labour and profit..........

doing it yourself is easy enough, but a 2 person job and labour intensive. a lot easier with ready mix though.

just my thoughts

 

[aaronjb]

Yeah I worked out some prices earlier and figured I could DIY it including plant hire for ~£2500.. but then ended up with a quote for £2500 and started to think it wouldn't be worth doing it myself..

But I'm paranoid that I'll end up with a base laid that isn't suitable for the garage when the garage company turn up :-/ for example - one guy who came to quote (who didn't seem interested in listening to what I wanted the base for) wanted to put a gradient on the whole base - which the garage companies tell you makes the base unsuitable..

Pondering DIY though I realise just how much I don't know how to do - simple things like.. how do you make sure the reinforcing steel mesh is at the right height.


Actually I'm tempted to just go with the first guy who came out and quoted £4k, purely because it seems like he actually knew what he was talking about - it's just a lot of money for a concrete slab

 

[studips]

setting the mesh at the right height is easy enough - a pile of block paviours work as spacers to sit the mesh on top of.

the £2,500 guy sounds sensible, but you would need to watch him - maybe say you'll have him, but you'll work with him. no need to try and beat the price down, you just being there managing the job will make sure nothing is skimped - as will seeing what materials come in - as i said about 8 tonnes of type 1, loose ballast to make 5mcu concrete would be about 8 tonnes of ballast, and for a c30 mix say 1:5 you would expect to see about 56 bags of cement turn up.

if all that goes in the hole, is not over wet, it's well tamped to encourage air out, then allowed to cure slowly - and dead level - then you know you have a good job.

but seriously, mixing with a mixer is just earning a wage the hard way - ready mix is the way forward.

 

[aaronjb]

Thanks for the advice, it's much appreciated

Actually I may be misquoting the guy slightly on the concrete, I think his exact words were more along the lines of "The bloke turns up with a mixer truck and mixes it on site" - googling a little makes this sound slightly less labour intensive than mixing it by hand, though he was clearly still planning to put it all into the shuttering by barrow.

I'm sure 75% of my problem is a certain innate distrust of people, if I just relaxed and bit the bullet it'd probably be fine.. right?


Ultimately as long as it turns into a large flat area of concrete the right size, strong enough to support the ~3t of concrete garage (plus cars), has two bits of conduit sticking out of it in the right place for the SWA and an area ~1.2x2.3m excluded with shuttering (for the eventual pit) I'll be a happy bunny!

 

[Hugh Jaleak]

If the guy has a 'Volumetric' mixer, it'll bring the dry ingredients along, then the driver can set the type of mix required on site, mix and discharge virtually as much or little as you need. (Subject to the capacity of the vehicle.) Only manual work is barrowing the mix to point of use!

If you decide to DIY you'll need to extend the edges of the slab beyond the edges of the proposed footprint of the garage, (you dont want the weight right on the edges). Also it is critical the base is level, too far out and the garage wont sit on it. If you're at all unsure i'd bite the bullet and let someone you can trust do the base. Get it wrong and you've wasted the concrete (which will then have to be broken up and disposed of), and need to start again. Chances are if the garage supplier isnt happy with the base they'll refuse delivery and charge you anyway.....

I had one put up last year by the 'Market Leaders', unfortunately I wasn't very impressed with the quality of the finished product. It was 'thrown' together, and took 2 visits by the aftercare guys, (neither of which were impressed by the standard of workmanship by the assemble team), to get it right. One panel was cracked, (replaced FOC), the up & over door was out of square so broke after a weeks use, the joints were pretty uneven, and the silicon used to seal the joints was sloppily applied, and missing altogether in places.

Rubbish was left in the garge for me to dispose of, then when the panel was replaced I was left with the cracked panel to get rid of.... Altogether they didnt give me much to recommend them on.

 

[aaronjb]

If you're at all unsure i'd bite the bullet and let someone you can trust do the base.

That's the part that's the problem, really.. finding someone I trust! So far the only person who has really inspired any confidence in their ability to do the job wanted £4000 for the base.. I'm a little iffy about the second guy (£2500) and very iffy about the one who just called me to ask what concrete mix I wanted and a couple of other things when I saw him write the answers down when he was here!


Mind if I ask which garage supplier you went with, by the way? Feel free to PM me if you'd rather not say on an open forum. The 'leader' in my little league table of prices & features right now is a place called White Rose Buildings up in Goole, with another company called nucrete right on their heels (oddly enough, both of them aren't that far from where I grew up .. which has no bearing on my choosing them, honest )

 

[aaronjb]

Actually here's a very pertinent question that just came to mind;

Roughly 50% the area of the 'new' base currently has the old brick garage with concrete base standing on it.

The final level for the new garage floor will be ~4" higher than this old concrete base.

Is it OK for the builder to put down MOT1/similar to raise the level of the rest of the site to the same as the old concrete base, then lay 4" of concrete over the entire area including the old base ... like this (sizes are erm, very approximate, ASCII art never was my strong suit):

Untitled

• aaronjb
• 9 Apr 2011
• 1

Or if things are laid like that am I just asking for a big crack running down the length of the new garage where the hardcore/old concrete join is? Bearing in mind the concrete will have a layer of A252 steel mesh in it.

 

[studips]

if the old base is settled then it won't be going anywhere, i'd be confident putting 4" of concrete and mesh over that. and a volumetric mix is good news - no left ofer concrete and no short delivery, plus it will be the mix specified and not 'that looks like a heaped shovel' much more my speed.

 

[aaronjb]

Good to know - thanks The old base has been there at least 4 years, probably 5 by now - although the house was built in 1970, the garage was put up when the previous owners sold off half the garden (and location of the original garage) and put this one in.

not 'that looks like a heaped shovel'

That made me chuckle it's almost like you've seen my Dad & me mixing cement! (Or making a cake.. much the same approach is employed)

 

[Hugh Jaleak]

That's what I did. New garage replaced an Asbestos garage, which needed to go because it was asbestos, leaked, sat in a slight dip so collected water when it rained, and was too small to get my car in.... (Car would fit, but then slight issue with opening the door to get out. You couldnt.... )

Former asbestos garage was removed. Area around existing slab excavated to suit, MOT type 1 laid, concrete with mesh reinforcing laid to new base requirement. Assuming existing concrete is sound it should be ok, although you may need to break some out at the edge to accomodate the requirement for 300mm of concrete and twin layer of rebar at the edges. I'd also allow 100mm minimum outside the footprint of the building, as thats where the weight will sit.

Main thing is to get the shuttering right, you'll use that to tamp from, if its out, the whole slab will be out.... Readymix company will easily supply CP30, you'll never get it uniform by hand mixing with a small mixer, and probably wish you'd never started before even getting halfway through.

Might be worth asking the garage supplier if they have any contacts who've done this job for them before. The agent for my supplier works with a team, he sells the building, he works with a guy who comes along to clear the site, his son lays the base and the supplier puts building up. Sadly, it was the suppliers people that let the whole job down. You have a P.M. about that...

 

[thatbloke]

Would it not be cheaper to buy a mixer off e bay , buy the cement and ballast in bulk, do the job your self then sell the mixer on e bay and get your money back? By the way you can pick up concrete garages on e bay for pennys , it took me months of trying to give mine away on freecycle.

 

[wombats]

How did you get on with your base? Looking at doing something similar.

 

[aaronjb]

In the end I found a local guy who came and laid the new base for me - cost me around £2000 ultimately for him and his assistant to be here five days, pull down the old garage, level the site, hardcore the half over fresh ground and build up the level of the old base side with the old blocks, pour concrete over the lot and set in conduit for electric, water and drains to the base.

A couple of weeks after that I had the new garage put up by Compton, then an NICEIC registered electrician came in and wired up sockets, lights etc in the garage.

 

[wombats]

Glad you got sorted out. I think i may try and do mine myself.

Then an NICEIC registered electrician came in and wired up sockets, lights etc in the garage.

How much did that cost as looking at doing something similar?