How to Stiffen Concrete While Keeping Long Work Time?

I would like to know the way to stiffen concrete (not too waterly) while still allow me enough time to work on it.
What I am trying to do is to level the basement floor. My floor is not level - the difference from one side to another side is around 3 inches. In order to level the floor, I am supposed to use concrete to build up a dam around the edge of the basement wall, then I can use a long wood block (2x4) that rides on the dam to level the floor. My question is about whether the concrete will be too waterly to hold itself up, especially in the area that I need to build the dam to 3 inches tall.
I guess I should add less water into the concrete mix to make sure it is stiff enough. But I am afraid that the concrete will dry too fast that doesn't give me enough time to build the dam very nicely. I guess making small batches will help in this situation. I am just wondering whether there is other alternatives.
I am planning to use concrete that has pre-mixed with sand (not small stones). I mention this just in case this matters.
Thanks in advance for any tip.
Jay Chan
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The hardening process with concrete isn't the result of drying--it is from a chemical process involving hydration of the lime in the cement. Using very cold water will slow the hydration process somewhat as well as doing the work in a cold air temperature (above freezing). Adding excess water to a mix will slow the set time by separating the cement particles with water. This causes a soupy mix which takes some extra time for the cement particles to compact sufficiently for them to bond together and results in a weak and porous finished product.
There are admixtures used by readymix companies which will extend the set time (delayed set) such as lignosulfonate. Check with the local suppliers for an "extended set admixture" or "delayed set admixture"
Regards,
John
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Thanks for the pointer. I will check it out.
Jay Chan
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What you are proposing requires a lot of concrete, do you have any idea how much that is going to weigh? Do you know how hard it is to move around and get the proper level ( I doubt if you really want it level, normally you want it to drain.).
Have you worked a slab that large before? Even a smallish slap requires a crew of experienced people working together, and then it is hard work. Working in a basement is usually more difficult than working on the ground.
I really think you should reconsider this idea of doing it yourself.
--
Joseph E. Meehan

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You are exactly right. From my failed attempt to level the floor two months ago, I know that this requires a lot of concrete (and the many bags of concrete were very heavy). Luckily, I have already raised the low area to within 1/2" to 1" of the leveling line. I have seen the end of the tunnel, and I cannot wait to get this over with.
For anyone who is reading this thread and is thinking of leveling a basement floor by himself, I have two suggestions: 1. You may find that living with bare concrete floor or painted concrete floor actually is not bad -- as compared to the effort of trying to level a basement floor. 2. You may find that spending the money to fire a pro to do this may be more economical than doing this yourself.

Actually, I want it to be level because I want to put tiles over it. The other side of the basement is left unfinished, and the drain hole is in that side of the basement.

Yes, you are right. This is really not a DIY kind of thing. But too late for me. I have already spent so much effort on this, and I have already emotionally committed to this project. If I could start this over with, I will either hire a pro, or I will just learn to live with the bare concrete floor.
Jay Chan
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You are quite right to say that. Now, after having tried and failed to level the floor myself (two months ago), I would think that I should have forgot about the idea of leveling the floor (for putting tiles) and live with the uneven floor and bare concrete floor. But now I am at the point of no return. I will have to get it done.

If I could started this over with, I would be better off hiring this out. But I am now so close to the finish-line. I really want to get it done.

90 minutes is more than enough for me. This means using extender is a good idea for me. Thanks.

Luckily, the floor is not sinking. The concrete floor was not leveled properly when the house was constructed back in 1950's. I have a feeling that the basement was not meant to be finished when the house was constructed. Therefore, making it level was never a requirement back then.
Jay Chan
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Yours is a good idea. Now, I just need to find the right material to build the form and prevent the thinly poured concrete from leaking out. Then, I don't need to worry about stiffening concrete and entending work time.

I probably will use leveling compound. They hold up quite well in thin pour based on my experience in my past failed attempt to level the floor. When I tried to knocked out the high spots that I mistakenly created, I have a hard time to knock it out if the high spots were make from leveling compound. The down side is that leveling compound is quite expensive. But I should not need that much if I only use it to form the dam around the wall.
Thanks.
Jay Chan
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