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I have bought a pre-mix "multi purpose" concrete. The mix appears to be mixed with sand and small stones.

I have seen Creating a concrete mix with smooth texture which is about how to make it smooth and this kind of answered my question but, I'm not totally fussed about it being smooth (well, I am, but that isn't my question)

The issue I have is, I'm leveling a floor by a tiny amount but the size of the stones are too big and I can't taper it as I'd like. This means at one side, the concrete may have a a height of 3 inches, and the other, 1mm.

I've put down a bonding agent, I've mixed the concrete, spread it out and of course, with stones/pebbles over 1mm high, I can't get it smooth/low enough enough in height.

I don't understand why there are these bigger stones in the mix. My own research shows nothing. My own brain tells me, it's to fill it out to reduce cost! If the stones were removed, more stand/cement would be needed and cost would go up.

If my brain is right, could I have sieved the mix first (and then add water as expected) to remove the larger stones to have produced a thinner surface (and would it still set)?

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    What you are looking for is "screed". This is usually a concrete / latex based compound that when made up can be spread thinly to level a floor. It is often "self-levelling", too. You may have to apply it in several stages to make up the 3" though!
    – SiHa
    Commented Nov 11, 2020 at 12:14
  • Can I? I got recommended to not do that as your idea was the same as mine diy.stackexchange.com/questions/204310/…
    – MyDaftQuestions
    Commented Nov 11, 2020 at 12:32
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    The aggregate in concrete is "filler" but it's not there to cheap out - it's part of the concrete mix and adds strength. Is this an extension of the question you noted above about your garage, or do you have more floors that aren't level?
    – FreeMan
    Commented Nov 11, 2020 at 12:39
  • No, it's all about the same thing. Floor not level, max height of self leveling was lower than I can do with concrete, so I researched and researched, put down a bonding agent, leveled but need to level by mm now! It could be I just apply this self leveling screed thing on top of the concrete to make it look nice and get a few mm more accurate to level
    – MyDaftQuestions
    Commented Nov 11, 2020 at 12:43
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    Does this answer your question? How thickly can I install self levelling concrete to fix a tilted garage floor?
    – FreeMan
    Commented Nov 11, 2020 at 14:11

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Aggregate gives concrete much of its strength. Stone is much stronger than common cement mixes, and the pebbles create interior reinforcement that's critical to performance. The gravel also reduces cost and water consumption, but that's not relevant here.

The problem with your plan is that standard concrete isn't designed to be structurally sound in such thin applications. It will be very brittle and prone to shattering.

Products that are designed for thin applications tend to have additives, such as vinyl or latex, which make them much more flexible and robust in thin applications. They're the right thing for the job. They'll also be much easier to work as they don't tear as readily when troweling.

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