Advice needed regarding a shed base.

[jones68]

Hi
I am finally attempting to construct a base for a Yardmaster metal shed, which is approximately 3m x 4m. I bought the shed in April, but due to the bad weather of the past few months, only now is work under way to construct the base. I have leveled the ground, dug a trench and cast the footings 350mm wide, 150mm deep, with a minimum depth below ground of 200mm. The footings are in solid clay. I now propose to lay two to three courses of concrete blocks (stood on edges), to make the base up to the correct height above ground, and then cast a concrete floor within the block area, with a damp course underneath.

[jones68]

Here are some photos to show how far I have got with the construction, not sure if it's done correctly, but it seems o.k. I compacted the concrete by treading it firmly into place, finally finishing off with a piece of 3 x 2.

The finished cast footings, note the 2 x 4 wood framework I used as a guide, don't know if I should have done this or not? The chippings I used were very fine 10mm or less, and the finished footings now have a 'glazed' appearance in places. During leveling, only a small amount of water was present on the surface.





Now I have a few questions.

Do I need an particular types of concrete block?

I know I have to remove all the organic soil from the centre, but what can I fill the centre with afterwards, can I use broken concrete, rubble and bricks etc to fill?

Do I need seep holes in the bottom course of blocks, and should I fill around the outside of the footings with chippings to assist drainage, or should I just use the clay that I dug out?

How thick should the finished concrete slab be, and do I need to use a reinforcing grid or whatever it's called?

That's enough questions for now, any help and advice would be greatly appreciated.

[lutonlagerlout]

no just standard 100 mm concrete blocks are fine,when you have dug any topsoil out of the centre ,you would then measure down from your assumed top of slab
say you have 300 mm,you could then do 100 mm clean hardcore,100mm of type 1(either crushed concrete or MOT) then a blinding of sand (to avoid tearing the membrane) then your DPM,then last but not least 100 mm of concrete @6:1 gauge

don't forget to wack the hardcore/type 1 in layers
cheers
LLL

[IanMelb]

I've put pea shingle around the outside of my shed and used two courses of blocks to get to level.

Have a look at this thread to see what I've been doing (although I can't guarantee that it's the best method)

[jones68]

Just over a month on, and I've now got 3 courses of concrete block completed, and am currently digging out the 'peaty' soil from the centre, leaving just the clay. I am going to fill the centre by using a large quantity of stones, and rubble because it is more than 2 foot deep in places. I will use some fine chippings to fill in between the rubble, followed by some 'proper' hardcore for the final sub base layer.

Here are some pics.





BTW, I may get the outside of the blocks rendered to help protect them , and intend to fill around the outside using chippings to help drainage.

Any help or tips would be greatly appreciated.
I will post some more photos soon.

This project is turning out to be a rather expensive garden shed base.

[seanandruby]

Are those weep holes at the bottom of the blocks? you need to fill those , or else the water will drain in. personally wouldn't shingle the outside of the base, unless you are going to build a soak away. i would fill with soil, maybe black jack lower blocks first. it is always best, if possible, to use engineering bricks below ground.

[lutonlagerlout]

why is it so high out of the ground?
i would have had it a course lower and dug a bit of ground away from the back side??
i would have thought 2 course of blocks was ample,otherwise you will need steps to get in your shed
other than that looks fine
regards LLL

[jones68]

I've spent a few hours today starting filling in with stones and bricks. The largest stones I placed flat on the ground and filled in between with the smaller ones with some chippings. The bricks and some of the larger stones, I smashed up with a sledgehammer into smaller pieces. The top part of the garden to the left of the shed is full of stones and bricks, so I have been digging them out. I also have a few tons of smashed concrete left over from replacing a floor in the house, most of it is small pieces, so I will use that as well. That lot should come up level to the 2nd block. Somebody suggested to me, that I fill in with soil up to the 2nd block, but I thought it would be better to use the stones and smashed rubble instead?

[jones68]

I had planned to have two courses of blocks, but there is already a significant slope at the back, which comes almost level with the third course of blocks, so some digging away will be required. There will be a step up at the front.

[jones68]

I have now filled up to the 1st block with a mixture of stones, broken concrete and gravel. It now looks like this.



I have enough to fill roughly to 3/4 way up the 2nd block, then I will have to buy some harcore from the builders merchants. Just wondering what type of hardcore I need?

[lutonlagerlout]

corporal jones you havent really answered my question??
why so high out of the ground?
from the piccies you have posted 2 courses would have been fine,just a little bit of digging on the back edge
if you lose the top block you can fill with 100mm deep of type 1 then concrete on top of that
the blocks can be used for your steps

yours captain mainwaring :;):

[jones68]

The reason I have decided to have it 3 blocks high, is because the garden backs onto moorland. During the heavy rain of winter (and summer), a lot of water can drain off the moorland and flood the garden. So I thought better to have the base high and dry. Although not obvious in the photos, there is already a substantial embankment at the rear of the shed base and removing more soil would leave the embankment with an almost 45 degree angle.

[lutonlagerlout]

ok jones no more dads army stuff then
i thought the 68 was your year of birth same as mine and you might get the joke
so your shed is 12 M2 so you need roughly 2 tonnes of type 1 for every 100mm you come up in height,so looking at your pics you need at least 6 tonnes of crushed concrete about £100 delivered
then 1.2m3 of paving mix concrete which would cost about £120 delivered,if you knock it up yourself you will need 2.5 tonnes of ballast and 12 bags of cement
due to the amount of hardcore etc i would make sure and wack it in layers and also use some steel mesh in the concrete
hope this answers your questions
cheers LLL

[jones68]

Thanks for the advice, much appreciated.
Now do I hire a wacker, or buy one new or secondhand?
Decisions decisions and more expense.

You know a friend suggested the following:
"Fill the base in with old bricks and concrete nearly to the top, and then make a "sloppy" concrete and pour it between the rubble, then level off." Needless to say, I decided not to take that advice.

Someone else suggested, "It's only a garden shed, just cast a concrete base directly onto the ground."

Which is why I came to visit this site to seek professional advice.

Here's another view, the large pile of stones to the left, I have used in the base.



The land behind the garden is common land moorland, and stretches for a few miles to the next town.

The next project after the shed is gonna be a path to the shed.
Then I can think about getting the garden and fences sorted out.

[seanandruby]

If you had asked and posted pics before you dug out the footings then the general consensus from brewers would of been for you to lay a base with flags or concrete.