On Thursday, 10 September 2020 at 14:03:32 UTC+1, Chris Bacon wrote:
On 10/09/2020 08:27, John Rumm wrote:
On 09/09/2020 20:02, Chris Bacon wrote:
Asked this over at Cormaic's, but no joy (maybe (much!) laterrrr, but
panic on, so here now). This is the slab I've just made with my Aldi
concrete mixer).

4.5 cu m by hand through a mixer is quite impressive! Was that all "one
pour" so to speak?
No, three lateral ~2m x 5m sections, each end taking the most concrete
due to keeled structure. I nave named my Aldi mixer "Wonky Donky",
because if you say that very s-l-o-w-l-y that's the noise it makes, the
drum's drive is pressed into the drum itself, which is not very
accurately made. Wonnnnkeeeee donnnnkeeee.
Nominal 6000mm by 5000 mm prefab garage for use as garden shed (by my
measurements it will be 6020 by 5035 actualsize).

Slab is 6050 by 5050.

Have I mucked it up and made it too small to use?

I have seen plenty of slab foundations that were made exact size, and
they have held up fine with brick garages on them...
I am on the horns of a dilemma. Say I'll have 1700kg each side, spread
over 6m length. 280kg to the metre, with most of the load being at the
bases of the posts. The load won't be as evenly distributed as it is
with brick.

OTOH my *other* "workshop" is similar, but is a single garage, and its
base slab is only just big enough. The posts are within 1cm of the edge,
the bays being set back ~3" due to being slotted into the posts.
However, that slab, which has been there for decades, is only around
3-5" thick, on "hardcore" of old bricks, china, broken concrete, the odd
copper pipe & all sorts. I'd guess the posts/bays are similar weight.
The new "shed" has 8" thick solid concrete keels over a DPM so should be
stronger, all else being equal.

The old:

https://ibb.co/TwsCYxF

The new:

https://ibb.co/dtR9ChW (first bay, DPM in, awaiting fabric mesh on
meshmen, shows 8" keel, 4" centre)
https://ibb.co/ZLg8sPj (work in progress, middle bay)
https://ibb.co/bz6Pnf6 (last section, showing mesh fabric on meshmen,
"front" of slab)
https://ibb.co/PY3cbrV ("The Diggings" with Wonky Donkey and a sunshade
for the concrete, doubling later as a cover to stop it drying).

I've done hundreds of pre-pour rebar inspections and that workmanship is better than most

I'm tempted to try it. I'm also tempted to trench out one side another
200mm and concrete that, although there are disadvantages there too.

Really, dont bother ... it's not needed and getting both side to act as a single lump is very hard.