Concrete slab finishing by hand or machine?

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Old 09-09-11, 12:20 PM
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Concrete slab finishing by hand or machine?

I have it down to two contractors for my new garage floor. Both propose a 5" slab using 4,000PSI fiber mesh concrete. One proposes a machine trowel while the other proposes hand finishing and does not recommend using a machine. Both promise a smooth hard and flat finish. I would like the smoothest finish possible for easy cleaning, as it will be a workshop and showroom. It will also be subject to freezing in winter. Please offer any information that may help me choose the best contractor.
 
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Old 09-09-11, 12:30 PM
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A vapor barrier (10 mil poly) will keep the slab from absorbing moisture from the ground.

If it can freeze, air entrained concrete (5-7% air) is a wise choice and does not add much cost.

Dick
 
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Old 09-09-11, 08:12 PM
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Thanks for the fast reply. Do you have any opinion on what is better, machine or hand trowel? The contractor who proposed a hand trowel finish claims the same hard smooth results but says hand troweling will not burn the surface like a machine. I don't know if he is blowing smoke?
 
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Old 09-10-11, 05:20 AM
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Air entrainment makes concrete very sticky. As such, it's hard to get a super smooth finish on it because it pulls up in chunks on the trowel blades. Interior concrete, even in garages, is not typically air-entrained because it's not exposed to the elements. However, since your vehicle may track in water which could turn into ice, you could put a half dose of air in it to ease your mind.
You can get a smooth, hard floor with either method (hand trowel or machine), but it depends on the skill of the finisher. Neither is "better" than the other. I've seen horrible hand trowelling and also horrible machine work. Likewise, I've seen both look equally as smooth and flat. Ask both contractors if you can go look at examples of their work (not photographs).
It is true that it's much harder to burn the finish with a hand trowel, but it can be done if you want. The burnishing can make it smooth and shiny like glass. If you want it shiny-smooth, go with the machine guy. Keep in mind that it will be slicker than snot when it's wet though.
Make sure that both contractors intend to cut crack control joints in the slab. If they tool them in while the concrete is soft, you'll need to go with the hand finisher. If you want them sawed in, either finishing method would work.
 
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Old 09-10-11, 06:26 AM
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I'm not a concrete pro, but as most contractors do I deal with the results. The part of your proposal that bothers me is the smooth finish and the potential freezing. At just the right times of the year a cold concrete floor will form lots of condensation and look like someone sprayed it with a hose. If it is nice and smooth it will be slick.

Cold temperatures are not good in any shop. I just retrieved a large aluminum tool from the back corner of my storage shed, night temperatures in the 50's now, and it was totally wet. Of course the AL was fine, but any metal that can rust will be at risk. Re-think those freezing temperatures to see if anything is possible to keep that space above 40.

Bud
 
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Old 09-11-11, 07:10 AM
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Just noticed that you say "fiber mesh concrete". Fiber Mesh is a brand name and is very coarse, so when it is finished you will see it plainly on the surface of the slab. More so if it's machine finished than if done by hand.
Maybe the contractors said "fiber mesh" when they just meant "fiber", similar to how people generically say "Kleenex" when they mean facial tissue. If they did actually mean Fiber Mesh, I would reconsider.
A better choice would be a "stealth" type of fiber which is very fine and much less noticeable in the finished product. It is typically made of single strands of fine fiber, whereas fiber mesh is actually a net made of coarse fiber. You may still see the "stealth" type on the surface, but it won't look like someone spread a handful of grass and finished it in as Fiber Mesh would.
There are many brands of stealth fiber, but two that are familiar to me are Nycon and Nytech.
 
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