concrete

[tellittojake]

I want to make a very smooth surface with concrete. In the average homedepot you see a concrete floor that is very smooth and you dont see any aggregate like a driveway. I purchased a few bags of concrete to experiment and was not able to get that smooth surface on top. I assume the heavier pieces settle and the cement mix rises to the top, but was reading too much water would weaken the concrete. I tried reducing the size of the aggregate and used more sand and portland cement in the next attempt and got a consistency like mortar and was too sandy and still did not get that smooth surface on top that I am trying to get. Help!

[lebomike]

It's all in the finishing , after the cement starts to set it is troweled for a period of time to get the fine finish, it is something that you have to practice, it does not come first few times around. Also they put a sealer in the concrete floors to help get that kind of shine.
I work with concrete every day at work.

I'm sure some others on here are more knowlegeable on this subject.

[crokett]

The smoothness you see is the concrete is troweled while it cures. The concrete should be mixed and poured as per the mfgr directions. In very hot weather you should cover it and or mist the surface with water so it does not cure too quickly After you pour then you work the surface to push the aggregate down and bring the slurry up. When water starts pooling on the surface it is too wet to work so you need to let it dry a little more.

This is an art as much as a science and the only way to learn it is to practice and see what doesn't work. Get a pool trowel - they have radiused corners instead of square. This will let you work the surface without creating ridges in the concrete.

[jking]

Also keep in mind the very smooth surfaces you see at Home Depot & the like were achieved using power trowels. It's a small powered machine the operator usually rides on & there are several trowels on bottom that rotate in a circular path. The average guy will be hard pressed to replicate that type of surface without a large amount of practice.

[iceman61]

An important note to remember is that whe you reduced the size of the aggregate you are also reducing the strength of the mix. Also, what is your finished product going to be, just a smooth pad or are you going to stain it?

[fbrend123]

Is this concrete work inside or outside? About 50 years ago my folks had a concrete patio built at the side of the house between the back door and driveway. My mother insisted on a smooth finish, and that's what she got. Why and how no one was ever killed or injured in the winter, I'll never know. I went down on it a couple of times, myself. Just a little bit of snow, and it was so slick that you could barely stand up on it. Was dicey even in the rain. Took quite a few years for the elements to roughen it up. Might have been a lawsuit waiting to happen. Just my two cent's worth.

[TheRic]

I'm no expert, just picked up a bunch from my brothers & cousins, who do it for a living.

As said above practice. There are so many variable (temp, wind, shade, mix content, time from start of mixing, temp of water when mixed, length of mixing, etc.) it is hard to say when the best time to trowel is. As you trowel you are working the stones down, and the cream up. The more you trowel it the more cream comes to the top, and the stones work down.

Also have been told the material (wood, aluminum, magnesium, etc) of the trowel makes a difference on what the top does. Sorry I forget what the different types do. Maybe someone else can chime in.

[Daryl]

On a well done concrete job you should not see any agregate. Before the trowel is picked up to finish the surface it is worked with a float. It is impossible to fine finish with a trowel if it was never floated. This is to push the heavy agregate down and allow the fines to come to the surface. I was probably twelve years old when Dad stuck a float in my hand and put me to work. I was kind of young when I decided that was not the life for me.

[backpacker85]

Also keep in mind that too much working with a float, and especially with the trowel, will bring up too much moisture and fines, and will result in a very weak concrete surface. This is why you see a lot more surface spalling in hard troweled surfaces than those with a rougher (broom or float) finish.

[RodKirby]

I so like to read all this stuff becuase I now KNOW I made the right decision to NEVER work with concrete

[gjat]

The finish on the concrete is determined by the troweling like lebomike and crockett said. It's not the mix. If you over-work it, you get too weak a surface. If you underwork it, the surface is rougher. And of course, different products are put on the top after curing.

[Seedy]

Start with a wood float. When it is no longer wet, use the magnesium float.When the mag float won't move it. switch to a steel trowel. Start out holding the trowel fairly flat. As the concrete gets harder, you can use more angle and down pressure until you get the finish that you want. You can make it look like glass if you really want to work that hard. Sprinkle a little water on it when it gets HARD. and trowel the H*** out of it. Good luck.
-Craig

[Tom Slick]

Bagged concrete can also create a problem. locally we only get "quikcrete" with decomposed granite as aggregate, it is impossible to trowel smooth because you can't push down the small gravel sized rocks.

for the super polished look in commercial buildings they actually have a machine come in and polishes the surface after curing.
http://www.concretenetwork.com/concr.../standards.htm

[182much]

Bagged concrete

Hello:
Having 20+ years working with concrete, I have learned a trick or 2.
When using bagged concrete I allways add a shovel of plain cement to the bag. This will help with the finish as well as the strength.
After you place the concrete and "screed" the surface, get a tamp which will force the aggregate down and also bring the "cream" up.
As others have said, start off with a wood float to bring up the water.
When the pools of water are gone, start using a Mag float which will help bring up more "cream"
Then when the mag float doesnt do anything, it's time to start using trowels. starting with a large one, and as the concrete starts to harden use progressivley smaller trowels to achieve the finish you want.
As said earlier use pool trowels, they are so much easier to work with as they wont leave any ridges.
If the slab is going to be exposed to the weather, put a broom finish on it, so there is less chance of slipping.
After you are satisfied with the finish, I suggest you mist it with water 3-4 times a day so the concrete wont cure as fast,
Good Luck

[DUD]

I'm with Mr Kirby on His answer. Bill