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Wes Billups
09-25-2009, 5:24 PM
I'll start by saying I've poured well over 100 yds of concrete in my life but it was always for footings or on the farm for cattle. I've never had to do anything that required a smooth/level finish. This weekend I want to mix and pour concrete in the trenches I made in my basement floor for plumbing. We're adding a bathroom in the basement and I cut the concrete, let a plumber do the piping, now the pouring is up to me.

This is probably as easy as pouring gets since I'll be screeding it off to the same level as the existing concrete. I'm just unsure about the best way to finish the concrete. My trenches are all 6 to 12" wide and 6" deep. I calculated I'd need 12-80 lb bags of concrete.

My plan is to mix, pour and screed as I go. Then trowel the surface smooth with a 14" magnesium float once all the mixing is complete. The troweling is where I have very little experience. I've only ever done a broom finish.

Do I wait a certain amount of time between screeding and troweling? Is the magnesium float the right tool or should I be using a wooden or steel trowel? Do I mix the concrete more or less wet for a nice smooth finish? Are there any things to watch out for?

Thanks,
Wes

phil harold
09-25-2009, 5:46 PM
a mag float can be used after you screed and before you use a steel trowel

the mag float is to bring the fines/cream up to the surface a trowel used at the right time can provied a smoother finish...

Scott T Smith
09-25-2009, 8:15 PM
"Mix" your concrete for strength - not finishing. Less water is better, as you will have less shrinkage and stronger concrete.

When finishing, keep a bucket of water handy and splash some drops on the surface when it needs to be wetted for finishing.

Typically you would use a steel trowel for finishing after the concrete has partially set up. It needs to be soft enough to work but hard enough to provide a stiff surface for the trowel.

Eric Larsen
09-26-2009, 11:53 AM
I'd get it "close enough" and then tile the basement -- no matter how good your screed job is, it's never going to match the old concrete. Here in Vegas, "good enough for the basement" porcelain is less than a buck a square foot.

Depending on climate, I'd probably add radiant floor heating, as well.

(But I am certifiably insane when it comes to overdoing projects.)

Cliff Rohrabacher
09-27-2009, 5:44 PM
you want adequate water in the concrete so that it sheets as it drips off a spoon.

Ohh wait that's maple syrup.

The drier you make you concrete the stronger it'll be. When you tamp it and work the surface you'll draw water up and that will become a smooth as you please as you work it.

Anthony Scira
09-28-2009, 5:56 PM
Have it pumped in and done in one shot. Once you do that its no that expensive to have guys that know what they are doing come and finish it right.

This has nothing to do with questioning your skills. Its more about my laziness and concrete is HEAVY bull work. Mixing all that concrete would take a whole weekend vs an afternoon with a pump truck.

Robert Reece
09-28-2009, 6:26 PM
This is a big gray area, but don't work it too much. You need to float it a time or too when it's pretty wet, then let it sit for a while before you hit with a steel trowel. Then let it rest between trowelings. The worst thing is to keep working it because you never let is set right.

It gets to a point where you can make a finger print, but when leaning on a trowel it doesn't go in much at all. That's the sweet spot.

Also like others said you can dust it with some water to keep the trowel moving nicely and to form a very nice top.

You might try an experiment with one bag in a 2x4 form just to get a feel for how long it takes to reach the sweet spot. You can make a stepping stone out of this experiment.

Kevin Arceneaux
10-01-2009, 8:45 AM
Make sure you vibrate it down so that there are no voids underneath the pipe.

If you are not using ties into the old concrete, you may want to make a real soupy mix of straight concrete, no aggregate, and brush it onto the old concrete. This will hydrate the old concrete, opening the pores in it, and help bond them together so they do not separate over time.

As stated above, you want to scree it first and let it set a few minutes, touch it to see how it is doing and then start the finishing.

Doing this is NOT a one person job, three would be a better number.

Wes Billups
10-01-2009, 12:10 PM
I forgot to get picture last night but a friend helped me mix and pour on Monday. Things went well and I'm happy with the finish I was able to achieve. I am a little disappointed that I wasn't able to fill the saw overcuts (1/8" kerfs) as the aggregate was too big. I'll have to stop at HD and see if they have any mortar mix that I could use to fill these in unless somebody has recommendations for how to handle the overcuts.

I'll try to get pictures tonight. Don't expect much, it's a concrete floor.

Wes

Chuck Saunders
10-01-2009, 6:38 PM
leveling compound will fill the saw kerfs