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  1. #1
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    May 2011
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    Default How to Sand Down Concrete Filler ?

    I need to fill cracks on my pre-cast concrete balcony -- I probably will be using quikcrete stuff like the pre-mixed concrete crack filler.

    Before I do, my question is how to sand down the filler to smooth out the filled area with the balcony. Like repairing drywall, the area will be lumpy and require smoothing or sanding.

    What tools & sandpaper are needed? a palm or belt sander, and is there specific masonry sand paper or just plain sandpaper??

    Thanks for any advice ?

  2. #2
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    Aug 2007
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    Default Re: How to Sand Down Concrete Filler ?

    Using your example of drywall, the easiest way to do it is to NOT make the mess in the first place.

    Cement products are extremely easy to work with while wet, and clean up just as easily as long as you do so while they're wet. When you fill your cracks, clean up the excess before it dries. Smooth the joints before they're dry. Do everything you can during the repair process to NOT make the mess in the first place.

    If you must grind on it after the fact, then you're going to need a masonry blade/grinding stone to do so, sand paper isn't going to cut it.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  3. #3
    Join Date
    Dec 2010
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    Houston Texas
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    Default Re: How to Sand Down Concrete Filler ?

    What Spruce said;

    Dampen the area first for a few reasons. 1- it keeps the new ceement from making a mess all over the surface of the old ceement and 2- it helps keep the old concrete from sucking the needed water from the patching ceement, allowing the patching ceement to cure properly.

    Use a good quality closed cell sponge from the tile area of Home Burrito along with a 5 gallon bucket of water to clean up as you go along.

    A diamond cup grinder will make quick and dusty work of grinding down any mistakes, but you'll have a nice clean spot staring back at you.

    The big question, why do you have cracks?

  4. #4
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    Default Re: How to Sand Down Concrete Filler ?

    I really don't know how the cracks ocurred. The balcony is 46 years old, and seems sturdy enough, so my plan is to fill the cracks and apply waterprook sealer and see what happens.

    Can you tell me more about the sandstone. I've seen it as a drill attachment and it would more likely cause lacerations to the concrete and smoothing it.

  5. #5
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    Default Re: How to Sand Down Concrete Filler ?

    Unless you have to smooth out an uneven surface caused by the crack, I would not recommend trying to grind on it, you're going to screw up the look of the patio and draw more attention to it than the existing or filled crack.

    Like we said, don't make the mess in the first place, clean up as you go, finish off the joint as you go, and be done with it.

    The grinding stone is usually diamond encrusted media that is attached to a drill or angle grinder. Anything you touch with it will be noticed, whether you fubar the surface or not. I would also recommend caution with trying to seal the slab, as if there's moisture in it, it will affect the finish over time and you won't be able to remove it. Also, sealers tend to make concrete slippery, something you don't want to do either. IMHO, it's just a bad idea.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  6. #6
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    Northern Virginia
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    Default Re: How to Sand Down Concrete Filler ?

    Quote Originally Posted by A. Spruce View Post
    Unless you have to smooth out an uneven surface caused by the crack, I would not recommend trying to grind on it, you're going to screw up the look of the patio and draw more attention to it than the existing or filled crack.

    Like we said, don't make the mess in the first place, clean up as you go, finish off the joint as you go, and be done with it.

    I would also recommend caution with trying to seal the slab, as if there's moisture in it, it will affect the finish over time and you won't be able to remove it. Also, sealers tend to make concrete slippery, something you don't want to do either. IMHO, it's just a bad idea.
    OK, I appeciate you hanging in on this . . . it's a balcony so I can't let it deteriorate slowly. A masonry contractor recommended pouring a 3/4" topcoat for $2,700. . What ? If you ask a surgeon, he/she's going to recommend surgery . . . so I'm taking a graduated approach. Sealing the cracks should be a first step, but then the wife will complain if there's a mess or rough spots; OK, don't make a mess is the advice.
    Maybe I mispoke about a sealant; what I meant is some sort of water repellant; is it the same or different substance.

    Then, I need to apply a metal lip along the perimeter of the balcony that will direct water straight down like a water fall; right now, heavy rains will travel down and on the underside of the balcony.

    What off-the-shelf metal strips can I use for the lip ? Basically, it would be 1-2" high and I would need to cover 36 feet of balcony ?
    What kind of concrete anchor to attach the metal lip ? those expensive Topcon fasteners ? or perhaps stainless steel screws and lead anchors?

  7. #7
    Join Date
    Aug 2007
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    Default Re: How to Sand Down Concrete Filler ?

    For now I'd only address the crack. It is best to see if you can figure out why it cracked and whether it's going to continue cracking or if it was a one time thing. That will probably take a tradesman familiar with concrete balconies and the structural support behind them. I don't personally think that overlaying with concrete is the thing to do, particularly if there are structural reasons behind the crack.

    The crack itself I'd fill with either a suitable epoxy repair or with a cementious product. I cannot recommend a specific, I've been out of the biz too long.

    Sealers, by definition, seal the surface. If your balcony has a decent texture to it already, then sealers won't become too slick once applied, however, if you've got a relatively smooth surface, it will become slick when wet. You might be able to add a little sand to the sealer or broadcast spread it across the sealer before it dries, which will reduce the slipperiness of the sealer.

    I cannot recommend a product to create or attach a drip edge to the balcony. Again, consulting with a tradesman familiar with this sort of thing would be of benefit.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

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