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Smoothing Out a Finished Concrete Floor

jjchill | Posted in General Questions on

My interior concrete floors did not get hit with a power trowel. Too many reasons to list them all but mainly the machine was too big to get through doorways and the crew was worried about vibrations floating the radiant tubing to the surface. Overall we are happy with the hand trowel finish but a few areas that remained too wet now have a slight trowel bump to them. Would a 400 grit take them down and blend in to the other areas or am I looking at hitting everywhere with some 400 grit to maintain consistency? We don’t want a gloss finish and I was hopeing to only apply a densifier and call it good.

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  1. onslow | | #1


    It might well be overkill, but you might try contacting a tile company that can do terrazzo floors. They have appropriate machines for large areas, but mostly they might be able to tell you how they finish the tight areas they can't reach with the big machines.

    Or possibly try fabric backed wet/dry sand paper on a rectangular drywall hand sander with very minimal water. They look a bit like the tools used for grouting. The kind with a solid rubber pad will behave better than the kind with the vacuum hose features used with mesh drywall paper. Mesh will degrade in water so look for the wet/dry rated materials.

    400 grit is way too fine to start unless the trowel ridges are extremely low in height. The biggest problem you face will be blending any work you do into the other areas. I would suggest experimenting in a closet or some area where a failure to blend can be hidden. A matte sealer might help, but I wouldn't want to mislead.

  2. jberks | | #2

    Most things you'll do to it will be noticeable. like if you take a sander to it, you'll see exactly the swirly areas you've hit. Its very difficult to get the right grit of a diamond pad on a polisher to match the texture of the existing finish.

    If the trowel lips you're talking about are high and you want to get them down flat, I suggest going very small and focusing on just the lip. Like I mean dremel small, or getting a diamond hand pad and slowly grinding just the lips down by hand.

    You'll still see where the lips are, but they won't stick up.

  3. Expert Member
    Michael Maines | | #3

    Here's a good overview of grit for grinding concrete floors. There are not shortcuts.

  4. jjchill | | #4

    Thanks for your help! jberks i like your approach and im thinking i will go that route first then polish if were not happy.

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