Sub base mess

[VanMarco]

Hello,

I am going to have a new concrete slab installed on my backyard for the purpose of putting a new
large shed on it.
The old one was sloping down a lot.
Basically, due to both pride, and my habits, I refused to pay to have it removed in the first place,
My use was always to spend time to save money, so as it is not very urgent, I ripped
it all myself.
Now as I suspected, the old slab did not slope 3" for no reason.
Upon removing the concrete, now the site is clear, and as you can see from the pictures, the
soil beneath is also sloping a lot. Basically on the 8mt width, 6mt are fine (only 3cm of soil to remove)
the last two metres toward the wall, there are about 90mm of unnecessary depth.
The new slab will be four inches, the old one ranged between 3 inches and six.
So my question is, as I'm also cheap on construction materials, (LOL) would be a good idea to fill
wherever it needs filling with crushed concrete, bricks, cement and fines, and then apply a geotextile?

It is my unexperienced opinion that dumping other silty soil on top of other undraining soil it is not
a very smart decision to do, the fine rubble (where I did put it) offer a much more stable surface.

I hope you can help me out, as even if I dont want to admit it, I'm a bit over my head with this, ahah!

You are free to laugh at me for thinking 30 sqm was an easy thing to do, I've even thought that I could do
all of that in just days, single handedly, ahahahah

Thanks in advance

Images
Area:

Slope:

Some fill:

Final depth

[seanandruby]

Van is the string line in picture 2 your finished slab level?
if yes then that is way to high. you need to establish your paving and shed base levels. is the ground sound where the shed is going? if so you can lay a 100 ml concrete slab, if not then maybe dig out any unsound soil and build up with crush. you can use some of the concrete you are breaking out if about 40 mlish. keep the questions coming and don't panic .
look here

[VanMarco]

Hello, thanks for the reply sean.
Basically as of now I panic because I can't figure out how to dig properly, meaning following the same depth, and I think the issue other than me not knowing how to dig, also that more than dig is scraping off, as where there is soil it's just a couple of cm to remove.

Yes those string lines, My idea to put those that high, now I've lowered them to 10 cm above the current slab, is the string line necessarly need to be at the current level or not? and when I have the string line how to keep the depth consistent?

I've added a new pic (thats the change in one day LOL) I think that for the far part that is way below the required level I'll get at least a bag of MOT1 :p

Where I'm adding the crushed rubble, I'm still 15mm below what is supposed to be, LOL



Thanks again

[lemoncurd1702]

Hi VanMarco,
String lines are fine for digging out, maybe better set at finished height and use a piece of timber cut to the required depth to dip down with. I personally prefer to knock some pegs in to finished height and check depth with a straight edge placed between them.

Don't beat yourself up about 10-15mm here and there and better that it's 15mm lower than higher. You will find that crushed rubble difficult to level at that size and you maybe better off topping it with 20mm down rather than the larger type 1.

[lemoncurd1702]

Also meant to mention.
Lay the concrete base with a fall in the same direction as the sheds floor bearers/joists so that there is no holding water.

[VanMarco]

Today was raining quite a bit so I didn't go ahead, ahah, good time to rest the muscles a little
Could you kindly kindly explain me the pegs thing? Thanks

[lemoncurd1702]

String line is fine as long as it is level.
I just find that spot levels are easier on the eye and don't get in the way as much as a string line. Knock the stake into the ground to the finished height and work from there levelling to more stakes about 2-3m apart. Use a straight edge such as length of 3x2 with your level on top to extend the levels reach.

The weather was a batten down the hatches day here too.

[seanandruby]

Establish your finished height. Knock a peg in at both ends at finished slab level. Pull a line from one peg to t'other. A line level placed dead centre on the line will determine if it is level. Where your fall will go measure down that peg to and mark it 1:60 to determine your fall. Do the same along the other side. Once you have your falls you can measure down to your dig level, sub base level, bedding level etc: as lemon said you can use a timber with relevant markings to dip down.

[VanMarco]

Ok pictures Update.

OK I CONFESS AHAH, IVE CHEATED! Basically a friend offered me to lend me his cool laser level for half an hour, It took less than 20 mins to have the pegs level, yes this is cheating but in the evening I've been able to dig out what needed digging, lol. Also found an enormous root which is for sure on of the leading cause of cracking of the old slab, I don't even have an idea from where it came from, there is nothing around for several metres, it doesn't look like wisteria roots, my bets are on a very, very invasive bush on the frontyard, but I dont know how is that possible that roots can go that far (its about 10 metrse from there) LOL.

Also I noticed that when I drop the wheelbarrow full of crushed rubble, the damn fines always ended up on the bottom and none on top where they are needed, so maybe wrongly, I have separated them as I hammer the rubble down, I drop the well, stones, and then I top everything up with the fines, it's a LOT better and stable than before, I'm also topping everything up everywhere

So Technically the digging is over, now I "just" need to produce another 15 to 20 wheelbarrows of "aggregate" to top up wherever needs topping up
I wanted to thank you A LOT for your kind support., Thanks!

Images:
Aggregate difference:



Large root (LOL)



Finished digging, puff!!



Hope you like it lol

[seanandruby]

I'd hate to see the the size of the spider casting that web :;):

[VanMarco]

Ahahah yes I forgot to write that the spider is out at the moment

[VanMarco]

So long time no updates, the work has been going on, slowly, mostly due to the lack of time to do it and a bit to the weather, however below I finished to fill up downthere, now as I don't have the manpower to deal with a ready mix delivery, I have thought I could do it in sections, it will take a long time but who cares, lol, the images shows the first section, Why I began on the left rather than the right is because on the right I have a bit of a mess (basically I can't put the side board there fully, as the nearby structure will serve as restraint and also the slab must finish there, lol, so I checked well on the left and Installed the formwork, its pretty stable and almost perfectly square. Only thing is the company where I ordered the materials for the concrete was supposed to deliver this monday, but they were out of stock of gravel so another day delay, lol.

here's the images for you:

Filled up area (finally!)


Formwork 1


Formwork 2


hope you like it lol

Also one question how early I can remove one of the sides form board so that I can proceed, the fresh concrete edge would only be used as a screed medium?

Thanks!

[seanandruby]

Well done van. Give 24 hours before striking shutter.
Thought you were going bigger with your Shed, men can never have to much shed :;):

[VanMarco]

Hi back, I've poured the form pictured above, I haven't got time yet to take pics, however I think I'm doing seeerious mistakes, LOL, but I knew the first one would not come PEERFECT, as I wanted, basically My mixer has some issue, either I mounted the blades wrongly or, more likely they sent me wrong ones, long story short I made half before I got tired to mix correctly what the mixer didn't mix, and the next day I did the other half (I did place a bulkhead). The "Issues" so to speak are that the first half, ok, too much water, the second one started a bit to set before I finished to well, finish it. At the end of the day it looks great anyway and I managed to smoothed it out just fine, the real issue is that either I'm doing my concrete wrong, I'm filling the form wrong, or I'm screeding wrong, I bet all of the above LOL. I suspect the first half will get a bit of a birdbath.
1. Concrete proportions: For reference, I used these proprortions by weight: 3.5kg Cement - 6kg sand 12KG gravel, To me, it looks there is a bit too much gravel, as if I were to follow the 1:2:3 rule it would be 3.5 cement 7kg sand 10.5kg gravel, am I wrong somewhere? I have about 10 14L buckets at hand. (I used 1.7ltr water to the above reference, and it came well, not too stiff, not too runny)

2. screeding and filling the form. Do I have to fill up the entire form before screeding? I did this on the last piece, and it started to set (I also was really slow doing it LOL) The first part I did went better because I filled -- screeded as I went. What's the best way to do it?
Also as I screed (and maybe because I either doing my concrete wrong or not filling the form properly) it happens that some coarse aggregate gets screeded away, taking away too much material leaving well, lower spot.

Now I have covered the smooth (so to speak lol) concrete with plastic sheet, and I will leave it in place for a couple of days, and yes I do know I could go ahead sooner, but my back begs to differ lol

I will update with pictures as I can

[seanandruby]

Sorry Van but you had me rotfling with your post :;): :laugh:
I really wish i lived close to you because i'd come and give you a chuck on free of charge. I think you are maybe filling the mixer to much, do it gradually shovel by shovel. You need to complete the slab in one go, fill the shutter up, screed it off then trowel it up.