# Odd concrete stain- simple fix or a nightmare in the making?



## CarolinaMom (Jun 30, 2014)

We moved into this house about 6 years ago. It is on the main road in our subdivision. It had a smoky stain running along the edge, just under the vinyl siding.  I didn't think much about it, just figured it was dust from the cars, and moisture/dew in the air just drips it there.   For the last 6 years, it didn't really change much.
30 days ago we put the house on the market to sell and of course thats when the problems start.

We were cleaning up the house, borrowed a neighbors pressure washer, and those stains won't come up.   We cleaned the driveway, the back patio, etc, but they won't budge.  IN FACT- they are now WORSE.   They are no longer dusty grey like they have been for the past five years, but now they are looking more black.

I have one idea, and I don't know how much this plays into it.  We had a black rubber welcome mat with a filigree design, that is at least 6 years old (it belonged to the previous owner) and it could be deteriorating and the black running into this stain.  When I pulled the mat away, the filagree design was there.  

We were thinking of using the new paint at Lowe's for concrete, but I don't know if the stains will show thru.  If there is a cause that needs addressed? Any ideas what it is?  On the right side of the porch, it starts about a foot in towards the door and run the length of the front of the house, getting lighter as it nears the left side of the house, but is under both windows.  The porch wraps about 2-3 feet around the corner of the house on the left side, the stain doesn't go around the corner.









Any ideas, suggestions are greatly appreciated.  Please keep in mind we are trying to sell it, not planning on being here any longer, trying to keep expenses to a minimum.  

Thanks in advance

ETA:  I live in the Carolina's.  The house is built on a slab foundation.


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## carnuck (Jul 1, 2014)

It looks like they used a chemical to wash the outside and didn't rinse it off good enough afterwards.


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## Chris (Jul 2, 2014)

You can try a mixture of muriatic acid and water with a scrub brush. The acid eats away at the concrete just a tad so if it is a surface stain that should work. If you do that you will want to wear safety glasses and gloves and cover your skin.


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## nealtw (Jul 2, 2014)

Do you have a slab floor in the house or is it structured with wood.


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## CarolinaMom (Jul 2, 2014)

nealtw said:


> Do you have a slab floor in the house or is it structured with wood.



It's a slab foundation, about 10 years old.


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## nealtw (Jul 2, 2014)

Where we are the concrete slab out side would be a few inches below the slab inside. They may have waterproofed the foundation to high and that might bleed.
Or you have a roof leak and water is washing something down behind the siding
You may want to get a siding zipper tool and remove some siding at the bottom and make sure there is nothing going on. If you find nothing there take dated photos so you can show buyers , there is now big problem.


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## CarolinaMom (Jul 3, 2014)

nealtw said:


> Where we are the concrete slab out side would be a few inches below the slab inside.



It is here too. 




			
				nealtw said:
			
		

> Or you have a roof leak and water is washing something down behind the siding
> You may want to get a siding zipper tool and remove some siding at the bottom and make sure there is nothing going on. If you find nothing there take dated photos so you can show buyers , there is now big problem.



That thought had crossed my mind, I was kind of hoping someone would rule that out,  could be like opening Pandora's box- nothing but trouble inside. 



I tried some bleach yesterday, some of it seemed to come up, so my theory of the deteriorating doormat did play a part in it, but it's not the cause of the problem, it was just making it more prominent. 

I bought muriactic acid and supplies and will try that next. I know it's dangerous stuff. I've been watching some youtube videos and reading articles on it, but if you have some pointers, feel free to post them. 

I had read that the acid can damage the vinyl siding, and many suggest using a garden sprayer but that just seems like it wouldn't give me the control I need right up against the house. I was thinking of just gently pouring it, and then, spreading with a plastic broom. 

How long should I leave it there? It will foam up right? Do I need to neutralize it with baking soda before rinsing? I am afraid of killing the landscaping right by the porch, or is the extra water in the rinsing enough to dilute it?


The plan is to do the entire porch, not just the affected area, because if it's still there after the acid treatment, then I will paint the porch and cover it. 

I never see moisture in those areas. It's dry even during bad storms. The porch is deep enough that the rain never makes it that far, and I never see it damp ( like I would expect if something is running behind the siding).    The spot that doesn't have any stain, is at the end, next to the driveway, and the end 2 ft get sun, rain, traffic, no stain there. 

Thanks for the replies.


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## nealtw (Jul 3, 2014)

I haven't used the acid so no help there.

Water does wick up the foundation and that is why there should be some exposed below the siding, you said the area exposed to sun does not have a stain. Perhaps a moisture test.

Lay a peice of clear poly on the concrete for 24 hours and see if water collects under it.


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## Chris (Jul 3, 2014)

I mix my acid 50/50 with water. I keep it in a bucket and use a brush to dip in then scrub or pour some out and scrub. I don't spray because it is dangerous enough in a bucket let alone airborne. Don't let it sit to long, you should be able to see it work immediately if nothing after a couple minutes than it is likely not going to work. You shouldn't have to neutralize it but I would rinse the area very very well afterwards. It is the same chemical you would use in your pool just in a stronger concentration. I have not had any ill effects on plant life from the rinse down but I wouldn't go pouring the stuff on plants. You can always mix up only a cup or so and do a test section to see if it works first.


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## Chris (Jul 3, 2014)

Remember it is eating away at the concrete slightly so don't let it sit on too long. I had a leaky bottle and now have a permanent ring on my driveway but it sat there a couple hours.


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## beachguy005 (Jul 4, 2014)

You can get a less caustic version at HD.  It's lower in fumes also.  The directions say to mix it in a plastic sprinkler can co I don't think you have to worry too much about your siding.  
I just did my front walkway and was concerned about runoff killing my lawn but it didn't.  Mix it into water, pour on your stained area, let it sit for a few minutes, don't let it dry and scrub with a bristle brush...not metal.  Rinse well.  Just follow the directions on the gal jug.
If it doesn't come out and you still want to cover it, you could use a solid concrete stain, or get a bigger welcome mat.


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## CarolinaMom (Jul 13, 2014)

Update:  

We tried the acid, it helped remove the stain but didn't really improve the appearance of the porch. 

Then the phone rang and a Realtor scheduled a preview for one of her customers, so that got us in gear.  Quick run to Lowe's to pick up some of the new thick restore paint. 

We got the section with the stain covered before she arrived- mission accomplished, LOL. 

Now that it's completely painted, it looks nice.  

Thank you for all of the replies.


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## CallMeVilla (Jul 13, 2014)

When doing concrete etching (in preparation for staining) I have used a plastic watering can to  distribute the acid.  Easier to mix and control.  Then you can use a stiff bristled brush to scrub the surface.  Wear chemical resistant gloves and DO NOT kneel in the acid.

You want the surface to be dry and let the acid sit for 10-20 minutes before scrubbing. That should really attack the stains.  However, do not let the surface dry, so scrub sooner if necessary.

Once you have done this, the surface should be clean.  If not, then concrete paint might be your only option.


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## slownsteady (Jul 14, 2014)

Put some protection on your siding in any case. The bristles from a scrub brush can throw some spatter (splatter?) that you might not even notice.


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## nealtw (Jul 14, 2014)

Pay attantion boys, it;s been painted already.


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## oldognewtrick (Jul 14, 2014)

nealtw said:


> Pay attantion boys, it;s been painted already.




Just cause it's not broke Anymore, doesn't mean we can't keep on  fixin it.


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## stadry (Jul 27, 2014)

that's odd,,, we acid-stain & NEVER use acid to etch as it uses up the free lime in the cement thereby rendering the stain less potent,,, nor do any pro stainers we know,,, IF we must clean the conc, we'll use a lo-rpm buffer, black pad, & tsp,,, we also stain wet - 1 sprayer for water & another for acid stain,,, 2 light coats allow more predictable results than 1 heavy coat,,, when i hear the acid-stain didn't ' work ' properly, its because of the aforementioned  :beer:


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