Making concrete look old & dirty

I need to patch some concrete outside and I want to be able to match the color (basically 'dirty looking') and make it look old & weathered.
Can I just add a little 'dirt' (i.e. soil) to the mix to make it look darker and dirtier or will this create problems such as encouraging organic growth or weakening the concrete (I would only add a little bit).
Any better ways to weather concrete?
Note: it's only a small patch so I was hoping for something simple and cheap...
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Don't use dirt. You can try to match the aggregate stone, and the sand by using a similar color. You can buy coloring also. Last time I bought mortar color powder was 20 years ago, and it was about 3 bucks a pound, smallest container being 5 lbs. Never colored concrete. If the job is small, you might look at aquarium sand and gravel to mix in with cheap sand and gravel to your portland. You'd have to test mixes, letting some set before you could see the outcome. There's other "issues" with patching concrete depending on what you're patching.
--Vic
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The job is *real* small - basically we have an old millstone out front as a stepping stone to our front porch (it looks really nice).
Whoever put in the millstone, filled the old central hole with concrete that matches the stone itself pretty well. HOWEVER, the fill is about 1/4 -1/8 inch short of the surface, so water still pools there forming ice in the winter which is dangerous...
I would like to level it off with a thin veneer of new matching concrete (erring if anything on the side of being slightly proud of the surrounding surface).
I plan to use a latex binder instead of water in the mix so it will bind better to the old stone and concrete.
I probably only need maybe 8-16 ounces total to make the patch so buying pounds of colorant seems like a waste...
For such a small batch I didn't want to starty buying and mixing up my own batch of concrete. So my plan was to use quickrete filtered of any of the stones plus maybe a little mortar (all of which I have hanging around) and add a small biit of something to make it look dirtier.
I just need to know what something to use...
Perhaps I would be best off adding some aquarium sand to the mortar mix I currently have.
Any suggestions?
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blueman wrote:

grout.
it comes in lots of different colors and is a cement product, so can be mixed with concrete with no affects. try a couple different colors mixed so it's blotchy.
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Read the replies to your post; if you already have, then reread them. There are several suggestions, mine included, that will work just fine. For under $5 IMO.
Joe
Joe
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IMO, since it's a real millstone, the axle hole should stand out. I'd get any color pre-mix in a can. Black might look good. Haven't done so I don't know which product, but I bet you could find something in a can quick browsing at the store. Cutting a piece of rubber to fit and gluing/epoxying it in might work.
--Vic
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On 12/3/2010 11:31 AM, blueman wrote:

We used ready-mixed stucco patch on our condo's conc. block/stucco both to patch broken stucco and as mortar to cover a hole with a concrete paver :o) It was to be painted and looked great afterward. For such a small defect as you describe, it would probably work but would need to be painted. Doubt it would last forever, but the precise center is probably not stepped on very often. Paintable, and acryllic craft paint is close enough to exterior paint. Or take some exterior paint, leftover, and mix in a tad bit of acryllic artist color. I've used artist colors...acryllic or oil...for scads of jobs that didn't need the quart/gallon size of anything. Have mixed up my own "paint" from varnish, stain from oil paints, lin. oil, min. spirits and a pinch of varnish. The stucco patch comes sanded and unsanded, don't recall if it is colored. If you rub some stones on the millstone, you could probably end up with enough ground stone to color the stuff you patch with. I don't use any reference texts...just mix up what I think will do the job :o)
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blueman wrote:

Interesting question. Since the space is only about 1/4 to 1/8 inch thick, I wonder how well whatever you put in there will stay in place. Maybe the suggestion about using tile grout will work, or maybe using concrete patch that they sell at Home Depot etc. will be better than mortar or regular concrete.
I did a Google search of online images for millstones. To do the same search, go to http://images.google.com/imghp?hl=en and type in millstone for the search. Do any of those images look similar to the millstone that you have?
Whatever you use to fill the patched area, would it be possible to grind off part of the millstone in a hidden area and spread that on top to try to do the match? Or, maybe drill some holes in the center part to help hold the patch and the use the drill dust on top of the patch to try to match the color?
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I like the drilling or grinding idea - extra work but that sounds like how an architect would approach it. One other thing: if it was me I would look at using thinset mortar mix - the stuff you set tile with. It comes in various colors, seems to be happy being in a thin layer, and it's sticky. I would favor that over grout. -- H
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Heathcliff wrote:

thinset is very soft and would wear away. grout is stronger. the suggestion above was to use grout to color concrete, not use grout by itself.
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.

be careful a buddy cleaned his concrete one summer preping to sell home in the spring.
he raised the grain of the concrete, damaged the surface. after a hard winter, cracked and spalled all over....
ended up replacing most of his sidewalk..
he also damaged his deck boards...... cost his a deck rebuild, which was OK I guess some of the joists were rotting, found when the deck was pulled up....
he gave away his pressure washer......
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NO! Concrete is sacred. Do not defile the mix with filthy additives.

Leave it outside for a couple of decades.

There actually are some approved colorants to help match the shade, but not the texture. Check local ready-mix companies, box stores, Google, etc. If all else fails, a dab of Lock-Ease dry graphite powder is chemically neutral and will not affect the concrete mix. The dry results will not resemble the wet mix appearance, so make a dry mix before adding water to get a close match.
Joe
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On 12/2/2010 12:40 PM, blueman wrote:

Go to Walmart, Michaels or other craft store, buy a couple of bottles of acryllic craft paint....mix gray, a touch of yellow, a touch of burnt umber, dab on lightly with a stiff bristle stencil brush. I used it on concrete to cover dark wood stain that spilled and it did a very adequate job. Any paint, if not water soluble, is just about impossible to remove from concrete.
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On 12/2/2010 12:40 PM, blueman wrote:

I've sprinkled iron/steel filings on new concrete then mist it with water. Cover it with plastic so it has time to rust before it dries out, keep it wet. I've also mixed some filings in with the concrete but it's really a guess at how much it will stain.
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