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)?
Best Answer
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.