# How to sand a concrete floor?



## Bob Mariani

A 4" grinder with a diamond cone shaped wheel.


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## Bud Cline

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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## 2249diy

*Concrete sanding follow-up*

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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## Bob Mariani

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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## kristen4hair

*A grinding experience...*

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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## JJ1

*Jj*



Bud Cline said:


> 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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## yummy mummy

JJ1 said:


> *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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## Bob Mariani

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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## yummy mummy

Bob Mariani said:


> 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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## JJ1

Bob Mariani said:


> 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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## Bob Mariani

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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## JJ1

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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## Bob Mariani

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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## fixrite

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.

cheers


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## JJ1

Sorry for the hyjack. As you can see I have been labeled a 'newbie' & need to brush up on my manners. My local tile 'experts' are telling me to get busy laying the tile directly on the concrete. The home is 10+ years old & what few cracks are there are very minor... 1/8'' in width or less. None of which have any signs of verticle heave. I was concerned & inquired with several about using a membrane product to cover the length of cracks. They all said the same...'don't waste your time'. I want to do it right....home owner on the other hand is more of a risk taker. He is not concerned with the potential for movent that could damage the tile. The slab was poured over a plastic vapor barrier. I assume this minimizes the risk for moisture moving upward. I am also planning to use modified thin set with the porcelin tiles. It is my understanding that this combination is what you would even use in outdoor applications. 
I did look at the Dirta product on-line & see clearly how it will take away all the worries. This would double the expense to the home owner I'm sure. I'd call it a solid insuranse policy. Thanks again for the input, J.J.
By the way, what are your cradentials? I am also looking forward to here BUD CLINE'S (Tile Guy) opinion.


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## JJ1

If it were my chose I would go with the concrete makeover. I have seen many commercial buildings with polished, stained & sealed concrete..... absolutely amazing. It's safe to assume that the wearabilty & low maintenance get high marks. In this case the home owner is gonna have their tile. Thanks, J.J.


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## 2249diy

Does anyone have any suggestions how I would find someone in my area to grind my uneven concrete or micro plane it for stain preparation?


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## Bob Mariani

2249diy said:


> Does anyone have any suggestions how I would find someone in my area to grind my uneven concrete or micro plane it for stain preparation?


 Check the listing at http://www.concretenetwork.com/?p=Websites


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## yesitsconcrete

part of the allure of acid-stain'd conc IS the antique look post-stain & seal'd w/a good sealer,,, IF you need to ' sand ' the floor, do it all w/clark oscillating machine,,, tsp & blk pad on a lo-rpm buffer to clean up prior to acid.

you might be able to find a guy who's grinding & polishing but i'd bet the min charge's $1,500,,, even tho its my work, i won't have my conc done at that price,,, just acid & sealer :laughing:


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