WAS: How Thick Cement Slab for Bottom Stair

I poured a new concrete bottom stair, replacing several layers of asphalt that was used to reach the original concrete block at the bottom of the wooden stairs. It looks pretty good.
I have a few questions on how to finish off the original block and the new concrete bottom stair:
1. There were "curing" instructions on the concrete bag. It said to either add a curing additive to the mix, or keep the concrete wet for 5 days. Since there was no rush to use the stair, I kept it wet. My question is, why does keeping the concrete wet cure it, and why doesn't just letting the concrete dry normally work?
2. I would like the new stair to match-up with the old concrete stair just above it. I bought a bag of top cement to spread a thin layer over both stairs to make them look alike. I was hoping to make a 1/4" layer, but there are some good sized pebbles in the mix that would make it hard to smooth out the cover layer. My question is, can I screen-out these pebbles and use the remainder to spread over the two stairs? Will this sand and cement layer be strong enough to not crack or break off?
TIA for any tips, suggestions, comment.
Manjo
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Manjo wrote:

Curing cement/concrete is not a drying process but a chemical process. The cement mixture needs the water as part of the chemical process. If it dries, it loses the water for the chemical process. The result is a poorer quality final product. Same goes if it is too hot or cold while the concrete is curing. Technically it is only really important for the first few days, maybe even the first week. Concrete takes upwards of 100 years to finish curing, but it is useable within days of starting the process.

I don't want to answer this one, as I know I don't know enough to give a reasonable answer.

Carolyn
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Carolyn Marenger


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Carolyn,
Thanks for the info on curing. I recently saw a docuemenatary on the Hoover Dam. The engineers ran cooling pipes through the 16 x 16 poured "blocks" that made up the dam to cool it. If they hadn't cooled it, the heat developed during the chemical drying process would have delayed full curing for 136 years.
Regards,
Manjo
carolyn wrote:

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Its not a drying process. It is a chemical reaction. Drying means that the water evaporates. So when you mix water with flour to make pasta, you let it sit so the water can evaporate.
When you mix water with concrete mix, the water never evaporates. It becomes part of the concrete, allowing it to form crystals, giving it hardness and strength. Concrete can set and harden even underwater.
S
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mrsgator88 wrote:

S,
Thanks for the info. I never realized the water bcame part of the concrete. Most critical to process or there would be no process. After 9 days, I can still see dark portions towards the back of the stair versus the white towards the front part. Still curing, I guess.
Best regards,
Manjo
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Manjo wrote:

Already answered in the other response.

No. You can't. Topping mix would probably need to be about 2" thick to have any strength at all. Plus it will not bond real well to the step. You can use a latex admixture to make it bond better, but it will not hold up to much time or traffic.
If you need to cover it, look into one of the surface treatments for concrete. More money and more work, but you will have much better results.
http://www.sikaconstruction.com/con/con-dealer/con-dealer-repairing.htm
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Robert Allison
Rimshot, Inc.
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Robert Allison wrote:

I'll check it out. The old step is rough and worn. It looks worse next to the new (white) step.
Thanks,
Manjo
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First of all clean the steps of all dirt and residue. if they are old there is no need to do an acid wash. Second purchase some concrete bonding adheasive (H.D. / Lowes) and apply this to the old steps. Third purchase a bag of "plastic cement" (H.D. / Lowes)++++ DO NOT ADD SAND+++ put some in a bucket or plastic mixing tub and add enough water to make it spreadable kinda like yougurt or a little thicker and rub this on the steps with a sponge float covering the entire surface. This will give the steps a new appearance and should come pretty close to the color of the new step.
Manjo wrote:

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Italian Mason wrote:

Italian Mason,
Is the plastic cement a type of epoxy? OR some kind of super portland cement mix?
If the plastic cement on the old step does not match the color of the new step, what is the "acid wash" that I should use on the new (almost white) step? I'd like to have both steps look as much alike as possible.
Thanks,
Manjo
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Plastic cement is a cement mixture with addatives that is used primarly for stucco applications it is portland cement (the kind that was in your concrete bag mix) and some other misc items. If you would like to match the steps then simply do them all... but I would wait a couple of weeks or more before putting anything over the new step. You can find plastic cement at H.D and Lowes or a materials yard and usually comes in a 90 lb bag which is about 70# more than you will need but now that you know how to do it maybe you can use the rest up some where else around the house. I may have made this to complicated by assuming that you may have this stuff around the house... you can also just purchase a bag of concrete resurfacer at the above stores that is all that crap I listed before in one bag .....sorry if you do buy the premixed bag i would still suggest painting the stems with the bonding adheasive (even the new one) the mix has it in it but a surface application will ensure a good bond.
Manjo wrote:

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Italian Mason wrote:

Italian Mason,
Thanks for all the tips and information. I'm sure I'll find a use for the other 70# :>). The stuff sounds versatile.
Manjo
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