The Brew Cabin

Firstly congratulations with an excellent site. Tony your efforts on this site are commendable. Im just 2 days I have learned so much about paving, however with that knowledge I have also got myself in a muddle.

Ok so heres the situation. I am trying to build a base for a Yardmaster Garage which I have not yet ordered. I am in the process of ordering sharp sand and sub base...
My plan is to lay down a sub-base then sharp sand and then slabs on top. A few things I am unsure about:

1) How big do the sub-base and sharp sand layers need to be? The garage will be used for a library, storage and gym. Since the load on in the garage will not be moving except someone walking around, does this alter the specifications from that of a driveway (where u have a moving load).

2) If the garage is bolted onto slabs is there a danger of it turning over during high winds? Would this risk be reduced if my heavy equipment is put on the slabs next to the garage walls?

3)Not sure which type of slab is best suited for my purpose. I saw one 600x600x50mm, wow although it looks manly and macho :) it looks rather impractical for handling...The smallest one I could see in B&Q was 400x400x28mm this seems much easier to handle but would the 28mm thickness be adequate? does it mean I have to increase the size of my sub-base layer?

4) while i'm asking I may as well ask how much of each layer I need assuming I am going to get the 400x400x28mm slabs. The garage size is 9'10''x17'2" or 2.97x5.22m

I forgot to add I am thinking a sub-base of 100mm and sand of 50mm. 0.3 tonnes of sand ...0.8 tonnes for sub-base. Also I would estimate 25 400x400 slabs.
All these estimated from your page :
http://www.pavingexpert.com/calcall.htm#focus09

I'm not sure using flags as a base for a garage is all that good an idea. Normally, a garage would be built/erected over a concrete slab, but then, normally, a garage would be used to park-up the car. Using flags as a base is ok for sheds, where the bearers help spread the load of the structure, and the flags provide a firm base to carry the bearers and further spread the load onto the ground.

Using flags as a base for a garage - well, all the load will be passed onto the few flags that are actually carrying the walls, while those forming the floor are doing nothing. This might be cceptable, but then, using those 28mm wafers is asking for trouble. They are intended for garden use, and can only just cope with the weight of a wheelbarrow, let alone the weight of a garge, and the loads imposed on it during storm conditions.

If you were insistent on using flags, then I wouldn't use anything less than a 50mm pressed flag: I'd prefer a 63mm thick flag directly beneath the walls. The plan size of the flags isn't as critical. 600x600 is a good size, or you could use the 400x400/450450 Vehicle Overrun Paving in a 50mm or 3/70mm thickness.

For the bedding, I'd strongly recommend a cement-bound mixture. the 10:1 bedding mix I describe on the main site is ideal. However, I think you,ve made an error in your calculations. The garage is roughly 10ft x 17ft, which, in proper metric units is roughly 3m x 5.2m, which gives us 15.6m² without allowing for any spread. Using a 50mm bedding layer, you'd need just over 1.5 tonnes of sand/gravel.ballast - that's 5 times as much as you estimated!

And for the sub-base, you need roughly 3 tonnes, possibly 4 tonnes by the time you allow for a bit of spread.

Given all this, wouldn't it be easier, and cheaper, to pour a simple 100mm concrete slab?

Thanks for your reply, much appreciated.

Good job you spotted that huge mistake in my calculations.

I was in favour of flags because I don't have the equipment to lay such a big slab of concrete myself. I had previously layed down flagged once for a very small shed base and so felt confident I could do it this way. I didn't want to go to a builder because of all the hassle involved...however since the concrete method seems best I have been looking around now. I had one come round today but he didn't even bother giving me references of his previous work. Very suspicious. Since I don't know anyone who can recommend me a person who could od this job I would be taking a big risk to pick a builder from the yellow pages. I have read your page on selecting builders there was one in my area listed under the vetted list but they don't want to do my particular project (no car access to back garden). I'm rambling on so gotta stop...

Out of curiosity would it be possible to lay this amount of concrete myself? from say ready mix bags...Would I have to lay it in say 2 or 3 rows ?

Laying this slab as a single concrete slab is much easier than I think you realise.

You have a garage that measures 10x17ft, which is 3.1 x 5.2m. Let's allow 300mm of spread to all edges (it may be that you don't need or can't accommodate such spread, but bear with me), which means you need to pour a slab that is 3.7x5.8m, a total of just under 22m².

As there is no vehicular usage, there's no need to use a slab any thicker than 100mm, so your excavation is reduced from that you proposed for the flags (100+50+28=178mm) to 100mm - you could even allow for a 50mm base of regulating material and still have less excavation and cart away!

Then, it's a simple bit of formwork/shuttering, which you can knock up using scrap timber or buy-in some 100x19mm boards from the BM and fasten them in place using some 50x50 pegs. Line the lot with a sheet of visqueen or other DPM material and you're ready for the concrete.

You can bring in ready-mix or you can mix on-site. If you bring in ready-mix, then I'd suggest you get one of those "Mix and Place" companies that turn up with a wagon full of sand, aggregate and cement, mix it on the wagon, and barrow it to where you want it. You need 2.2m³ which would cost something less than 300 quid, depending on where you are in the country.

To mix yourself, you need a little mixer, which you can hire for 25 quid. Then you need approximately 2.6 tonnes of gravel, 1.3 tonnes of sand and 28 bags (25kg) of cement. If you use one of the DIY sheds, they can supply the sand and gravel for around 125 quid, and then the cement would cost another 70 quid or so.

Mixing that quantity of concrete in a single day is eminently feasible, but it would be much easier if you have a mate to help out. As a rough guide, I would expect two lads 'in the trade' to mix, pour and finish 2.2m³ of concrete in around 2 hours, so it might take you 4-6 hours.

If you mix to a reasonable slump (sloppiness), the concrete will more-or-less level itself when you pour it into place, and then it's a real doddle to tamp it level with a length of timber and float it to smooth finish. Cover it with another sheet of visqueen and leave it overnight (best if it's a frost-free night).

You will ache like you've never ached before, but a hot bath and a good night's kip will sort you out, and, a few days later you're ready to erect the garage.

Using the flags method, you're looking at 4.5 Tonnes of sub-base, 2 tonnes of bedding and then all the sands and cement for jointing, along with 1.5 tonnes of flags (130+). I reckon that lot will take you at least 3 long, back-breaking days to lay.

Get yourself a price from "Spot-Mix" or Mix-Mate" or whatever they're called in your part of the world, and weigh up the costs. It's good value, in my opinion, and a lot less achey! :)

Thanks for the comprehensive reply. I found that extremely useful.

During the week I have been looking for those spot-mix as u call them :) ...unfortunately that method doesn't seem feasible because the site for the garage will be behind the house and the delivery truck for the concerete will have to wait a heck of a long time while I wheel barrow it to the site. It would block traffic on road etc etc....

So I have been exploring the builder option again...(instead of discussing the builder i have in mind here I will email you).

You've missed the key point......it's not you that does the barrowing - they do all that for you!!

And the wagon 'hangs around' until their lads have got it all barrowed in, whether it's behind the house, at the bottom of the garden or anywhere else. :)

The ones that I asked they said they don't do the barrowing. I would have to barrow it...

Maybe its because they're more "commercial" hmmm some smaller operator may barrow it for me, then again there weren't many in the yellow pages. Me thinks I may have to find this type of contractor from word of mouth or something

Whereabouts are you? Look for Mixamate, Spotmix, Placemix as company names, as these tend to have franchisees in most urban areas.

I'm guessing that you've asked a normal readymix company, such as RMC or Pioneer - these don't do the barrowing, but then, they charge only for the concrete whereas the mix'n'place guys charge about 25 quid per cubic metre more than the readymix, but they do all the humping. :)

I see from your profile that you're on t'wrong side of t'Pennines, so here's a few companies that might be able to help thee...... ;)

Con-a-Crete
Leeds
Tel: 0113 282 7310

Mixamate Concrete
Leeds
Tel: 0113 287 4546

...or try the Spotmix website