# Concrete slab not smooth on top - What did I do wrong?



## HTFreak (Mar 24, 2014)

I used this and used a 2 x 4 wider than the width of this slab and I went
back and forth over and over while it was still wet to try to smooth out
the top. 



My opinion is that I probably used the wrong type of concrete (60 lb Sakrete bag) because this concrete mix had too many stones, hence the huge amount of stones sticking out all over on the surface???


Do better quality mixes have less stones?


What did I do wrong? 



https://www.homedepot.com/p/SAKRETE-60-lb-Gray-Concrete-Mix-65200940/100321247


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## SeniorSitizen (Sep 10, 2012)

You did a dry mix just like everyone recommends. Nothing wrong with the product.


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## SeniorSitizen (Sep 10, 2012)

Try a slump that flows and / or a pumper can pump next time.


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## Msradell (Sep 1, 2011)

You also didn't come close to finishing the concrete correctly. You used a 2x4 which is a good way to start smoothing the concrete. However to get a nice finish there are 2 additional steps, floating and troweling. The floating brings the "cream" to the surface so the rocks are not at the top surface. You trowel after that to get a very smooth finish.

A type of concrete you used was just fine, it's a technique that needs improvement.


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## stadry (Jun 20, 2009)

*you're right, you used the wrong material - shouldda used what comes in 80# bags :surprise: :vs_mad: i'm kidding, of course,,, we use that stuff almost daily
listen to radell & sr- a STRAIGHT 2x4's a screed used for initial leveling,,, if you let it sit long enough, the addl 'bleed water' will rise to the surface,,, you can then broom it off,,, IF that texture's good enough, let it cure,,, otherwise trowel*


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## SPS-1 (Oct 21, 2008)

I gotta think either you mixed it way too dry or way too wet, and/or your screeding technique was way off. I assume you made a wooden form for that and screeded with a 2x4 supported on the edge of the form. Should be getting pretty nice finish with just screed - no trowel. Watch a few YouTube videos.


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## HTFreak (Mar 24, 2014)

SeniorSitizen said:


> Try a slump that flows and / or a pumper can pump next time.



Thanks. Can you explain what you mean by "or a pumper can pump next time"?


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## John Smith_inFL (Jun 15, 2018)

my questions are: 
what is the slab used for and how big is it ??
and what purpose do the rings serve ?
and - how many do you have to make ?
the hand trowel or float tool is used after the 2x4 screed
to make it as smooth as glass. (some practice and experience required).
depending on its use, you may be able to reframe it and pour a new 1" top.
and if you need a smooth round top edge, there is a tool for that too.
(YouTube: How to Pour & Finish Concrete).


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## SeniorSitizen (Sep 10, 2012)

HTFreak said:


> Thanks. Can you explain what you mean by "or a pumper can pump next time"?


**********************************************

On jobs - _inaccessible_ - for the truck there are pumps available to pump the mixture where it needs to be. This particular pumper had to tell one ready mix company to shove it being they were determined to mix a slump too stiff to be pumped.

BTW, the sidewalk job in the previous pic had just been screeded with a 2x4. With a little Jitter Bug action of the 2x4 the water / cream is quickly brought to the top and rocks pushed down. All that remained to do was broom when the time was right. 

On DIY jobs don't be concerned about a 8-10 inch slump. That walk is only 2"thick in the center and without any steel. Withstood a fork lift loaded with shingle bundles driven by an idiot Lowe's truck driver. He couldn't drive a truck either.:vs_mad:


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## diywizard (Sep 22, 2019)

Yeah, all you forgot was to trowel the top for a smooth finish after you 2x4 leveled it.
You could skim coat it with filler and get a smoother finish if that's what your after?


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## stadry (Jun 20, 2009)

*possible - maybe just slid the screed over the surface w/o sawing back & forth,,, even doing that would've resulted in a better finish, no ? never saw such a surface but i don't know this fellow either so its his word it his work*


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## AlWood (May 29, 2019)

You have to use a darby, your 2x4 or some sort of float to sort of jiggle the concrete to bring the finer particles to the top and let the stones sink or it will set with stones on top like this, You can likely put a topcoat on it, may need to add acrylic fortifier to it to make it stick, and wet down (damp, not soaking) with a spritzer or something to make it stick better, or use a product intended as a top coat that's already done this.


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## stadry (Jun 20, 2009)

*the accepted & recommended specification on topping old conc w/new is to make the surface of the old 'surface saturated dry',,, defined as surface won't absorb any more water BUT there is no standing water (puddles),,, garden hose/sprinkle can + broom is the easiest method,,, flood the surface til old conc won't accept more wtr then broom off any puddles,,,this prevents old conc from absorbing new conc's moisture & weakening bond strength*


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## AlWood (May 29, 2019)

I use a pump sprayer and mist thoroughly


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## stadry (Jun 20, 2009)

*even a blind squirrel,,,,,,,,,,,,,,,,,,,,,,,*


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## HTFreak (Mar 24, 2014)

Johnny_inFL said:


> my questions are:
> what is the slab used for and how big is it ??
> and what purpose do the rings serve ?
> and - how many do you have to make ?
> ...



Thanks. :smile::smile::smile:



The slab is to cover an outdoor sump pump.
The rings make it possible to lift the heavy slab
I just needed to make 1.


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## stadry (Jun 20, 2009)

*standard hdpe sumps're only 18" in diam,,, think you could've bought a piece of flag/lime stone,,, but, alas, then we would never have met *


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## Yodaman (Mar 9, 2015)

I think you have the idea now. Screed to level, float to settle stones and bring water to the surface, then trowel to smooth. One step I don't believe anyone mentioned, is to vibrate the wet concrete. This will also settle stones and bring air bubbles to the surface. Small project like this you could tap the form edges with a hammer. 

The whole finishing process takes hours. Not that you would work a small project like this for hours, but you can not rush the curing process.


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