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Old 02-21-2009, 02:58 PM   #1
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How to sand a concrete floor?


I am trying to prepare an interior concrete floor for acid staining. About 3" out from an exterior wall the surface is very rough & slightly raised. Is there a way to sand this service so it is more in line with the rest of the room? What type of sander could be used this close to a wall?

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Old 02-21-2009, 04:00 PM   #2
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How to sand a concrete floor?


A 4" grinder with a diamond cone shaped wheel.

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Old 02-22-2009, 10:45 AM   #3
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How to sand a concrete floor?


Anything you do to the surface of that floor WILL be reflected in the results of the acid staining. IT WILL SHOW! I wouldn't reccommend using a grinder on just a small area. The texture of the surface as well as the makeup of the cement will determine the results of the acid staining. Grinders are very aggressive and there is no going back to fix it once the damage is done.

You could rent a heavy duty floor sander and use silicone carbide sandpaper to abraid the entire floor surface thereby repairing the area of concern at the same time.
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Old 02-22-2009, 01:14 PM   #4
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How to sand a concrete floor?


Thanks Bob & Bud:

At Lowe's they suggested a belt sander with coarse sand paper (because it would be easier to control.) Do you think even the amount taken off with a sander would alter the way the acid stain is accepted?
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Old 02-22-2009, 03:24 PM   #5
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How to sand a concrete floor?


What Bud is trying to say is that you do not want to make the texture of the concrete any different than the bulk surface. Sanding or polishing will seal the pores and not allow the same penetration of stain. I suggested the grinding option because I assumed you were trying to get a fer rough surface knocked down. Tread lightly with any method you use.
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Old 02-24-2009, 10:47 PM   #6
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How to sand a concrete floor?


It sounds like what you have now would give you an uneven stain absorption, anyway. Grinding is the only way to level it, with the diamond disc that was mentioned, but you will end up with all those little pebbles showing. You might try lightly grinding the whole floor to give it that uneven texture all over, maybe in a random circular pattern. A solid color stain will hide more than a semi-transparent, and there are some cool spray techniques where you can mix a couple of colors and get even more hide. Grinding with the hand-held grinder is hard work. That's what I have (a little) experience with.
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Old 03-05-2009, 01:04 PM   #7
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Anything you do to the surface of that floor WILL be reflected in the results of the acid staining. IT WILL SHOW! I wouldn't reccommend using a grinder on just a small area. The texture of the surface as well as the makeup of the cement will determine the results of the acid staining. Grinders are very aggressive and there is no going back to fix it once the damage is done.

You could rent a heavy duty floor sander and use silicone carbide sandpaper to abraid the entire floor surface thereby repairing the area of concern at the same time.
Hey Bud, I think what you are suggesting will work on my current project. I am tiling a basement floor (1000 sq, feet). The floor (CONCRETE) appears to have a clear sealer on it.... does not pass the water drop test. I rented one machine to take care of the bulk of carpet glue & in the process thought it was also scuffing the sealer off. I got a good scratch texture to it but it still will not absorb water. I plan to rent another machine this weekend & would like to get the right equipment to do it. What do you recommend? Thanks, J.J.
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Old 03-05-2009, 09:59 PM   #8
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How to sand a concrete floor?


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Hey Bud, I think what you are suggesting will work on my current project. I am tiling a basement floor (1000 sq, feet). The floor (CONCRETE) appears to have a clear sealer on it.... does not pass the water drop test. I rented one machine to take care of the bulk of carpet glue & in the process thought it was also scuffing the sealer off. I got a good scratch texture to it but it still will not absorb water. I plan to rent another machine this weekend & would like to get the right equipment to do it. What do you recommend? Thanks, J.J.
I am curious as to what the water drop test is? I am also planning on putting tiles on my concrete floor.
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Old 03-05-2009, 10:10 PM   #9
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How to sand a concrete floor?


When a drop of water is placed on the concrete, it should be absorbed into the concrete. If it just sits there, the surface of the concrete will no accept a stain.
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Old 03-05-2009, 11:22 PM   #10
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How to sand a concrete floor?


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When a drop of water is placed on the concrete, it should be absorbed into the concrete. If it just sits there, the surface of the concrete will no accept a stain.

Thanks Bob. Well mine definitely won't accept a stain. But I still have to sand the paint that is on it even though I am putting on tiles.
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Old 03-06-2009, 09:37 AM   #11
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How to sand a concrete floor?


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When a drop of water is placed on the concrete, it should be absorbed into the concrete. If it just sits there, the surface of the concrete will no accept a stain.
Maybe I am not water testing my concrete properly. A small 2'' puddle will sit beaded up for 30 minutes +/-. It wiil begin to soak in around the edge of pour. I had a Lowes rep tell to let it stand for a few minutes & then wipe it up. If the concrete is left with a darkened wet stain it is penetrating. I also mopped the entire area twice. Each time I used a wet but not soaked 24# commercial mop. A 10' x 10' area would be dry in minutes. This leads me to believe that my scratching the surface was succesful. What do think?
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Old 03-06-2009, 12:48 PM   #12
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How to sand a concrete floor?


If the water does not bead and the area you placed the water over does not contain any dry spots, then you are good to go with the staining. (as far as absorption test goes) You can fix the surface by chemically etching the concrete prior to staining.

You also need to be sure that not too much moisture transmission from below the slab is occurring.
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Old 03-06-2009, 02:36 PM   #13
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How to sand a concrete floor?


Sorry for any confusion.... I am tiling. I will be using 13 x 13 porcelin tile set on modified thin set. To clarify the machine I used did leave an obivous scratch pattern to the surface. Just enough to see it & feel it on your finger tip. I need to know if my thin set is gonna stick.... don't want to find out the hard way. Thanks, J.J.
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Old 03-06-2009, 04:35 PM   #14
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How to sand a concrete floor?


oh, so you tried to hyjack this thread. Three things to be concerned about.
1) Concrete is clean and surface is prepared.... (you have done this one)..
2) Moisture transmission from below the slab. Did you test for this?
3) Concrete moves, you do not want to transmit this into the tile How are you handling this one?

I would suggest using unmodified thinset and Dirta. It will handle problems #2 and #3 and then you are ready to tile
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Old 03-06-2009, 07:29 PM   #15
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How to sand a concrete floor?


Have you considered having the floor ground down and polished? I have seen this done a few times and it is stunning. The last place I saw it done they ground down about 3/4 of an inch and the stones in the concrete looked great. Just food for thought.

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