FAQs about stains & discoloration on concrete surfaces.

Methods for removing un-wanted discoloration or stains from concrete. This article series provides a catalog of types of stains found on concrete surfaces: walls, floors, ceilings, including un-wanted stains from various causes & deliberate concrete coloring processes, stains, or acid treatments.

Concrete Surface Stains, Diagnosis, Causes, Cures & Concrete Coloring Products

These questions and answers about diagnosing the cause of and removing stains on concrete surfaces were posted originally

at CONCRETE STAINS: ID & REMOVAL - be sure to review that article.

[Click to enlarge any image]

Stains on concrete sidewalks, porches, or interior concrete floors may be ascribed to a variety of sources that we list in that article.

 

On 2020-11-22 - by (mod) -

Jimmy

In your photo in the circled areas I see what looks like rust stains, perhaps from water leaking into the concrete structure where it's rusting iron re-bar or iron mesh reinforcement.

On 2020-11-18 by Jimmy Akcaoglu

Why do I find yellow stain marks on the concrete wall panels?

On 2020-10-30 - by (mod) -

If it really is troubling you could try cleaning the surface with a dilute muriatic acid solution but be careful that's a dangerous chemical and it will also kill any plants that you get it on as well as put out your eye if you get it in your eye

On 2020-10-29 by Jeff

Thanks for the reply. I don't know the conditions in which it was poured. But the house was built in 2017 in Bend Oregon.

It sure does look like a plastic sheeting pattern. How about the darker splotchy pattern? Same thing? Unlikely removable? I have another pic that might be a sealer fail. Could you confirm?

On 2020-10-29 - by (mod) - plastic sheeting can leave pattern imprint

Jeff

I can't know for sure from just a photo but typically when I see that pattern it's an imprint left in the concrete surface due to variations in water level during curing when new concrete was covered temporarily with plastic sheeting - a step often done to prevent too-rapid drying or occasionally as part of protection from cold weather.

Can you confirm the conditions under which this concrete was placed and also tell me the country/city of location?

If it's what I think, there is no way to simply wash this off as we're seeing variations in the actual surface texture of the concrete; you'd have to have the concrete polished or perhaps polished and stained.

The good news is exposed to weather these variations will probably diminish.

See these two concrete stain removal guides from the U.S. GSA:

US GSA REMOVING FINISHING & CURING DISCOLORATIONS From CONCRETE [PDF] U.S. General Services Administration, retrieved 2020/12/14

U.S. GSA Poulticing Curing Compound Stains From Concrete [PDF] retrieved 2020/12/14
Excerpt:

Curing compounds often disappear from concrete with the effects of natural weathering. However, if this is not aesthetically acceptable, chemical agents may be used to assist in stain removal.

On 2020-10-29 by Jeff

Hello- I have some patterns on this concrete I was hoping someone could Identify. I'm trying to clean the slabs up as part of a pressure washing job. Any Ideas what it is and what to use?

On 2020-09-23 - by (mod) -

Shaun

That's pretty puzzling, but we do have some clues that might suggest something to you:

- I see what looks like a clear heel print in the brown stain - suggesting that someone stepped into whatever was causing the brown coating

- I see what looks like brush marks - have those always been there or are they new? If new that might suggest there was a spill and an effort to brush it off

- you report that this is brand new and sudden

Those MIGHT mean that there was a spill in the drive and an effort to clean it; Or an effort to apply a coating or stain that has gone awry, perhaps with sun or weather exposure.

THese are nothing but guesses

Does it smell? If so like what?

On 2020-09-23 by Shaun

I came home after work to find a large area of our shared concrete driveway stained. It's a splotchy light brown substance and adhered to the pavement. I would like to know what it is and how to remove it. Thanks! Shaun

On 2020-08-17 - by (mod) -

Daniël

When concrete's pebbles show at the surface, I don't think it's a cover thickness issue but rather how the surface was worked or finished.

On 2020-08-15 by Daniël Verveer

I bought a truckload of precast slabs to use as pavement for my driveway and footpaths around my house.

There are many ptoblems, like wholes from poor vibrating the mold. These slabs are finshed on the top with a layer of intrinsic coloured concrete using dies like bayferrox.

One disturbing fault is the 'panter print' , looking like small stains or clouds. But could be pebbles shining throug the coloured layer. Does this mean the cover is unsufficient ?

 

On 2020-07-09 - by (mod) -

There are mold genera/species that can grow on concrete, particularly when there is organic dust or debris on the concret surface.

But that mottled dark staining combined with what look like vertical stripes could simply be artifacts of the original concrete form work or condensate or other water running down inside the forms.

On 2020-07-09 by Janice

Stains on smooth indoor concrete / (cement plaster?) in rental appartment.

In this room there was mold in the winter due to insufficient venting, although on the ceiling, not on this wall.

Could this be mold as well?

On 2020-04-21 - by (mod) - spots on new covered patio

Jennifer


What am i looking at - what surface?

The spot photo is great but

Can you post a second photo giving more perspective.

Is this a damp spot or an oil spill on fresh concrete?

On 2020-04-20 by Jennifer

What are these spots on my fairly new covered patio caused by? How can I get rid of the spots?

On 2019-11-22 - by (mod) - Looks like something ate through the cement and burned.

Kp

My guess is that there was an inclusion in the concrete at the spot that was exposed to enough moisture that It produced rust or exfoliation on a metallic material that could have been a mineral chunk or even a nail or piece of iron in the concrete.

That rust is of sufficient strength to pop off the surface of the concrete and to make that red stain. I would clean the area and simply patch it with a concrete patching compound

On 2019-11-22 by kpmsassy42111

Found this spot on my garage floor. Literally was not there 2 dats ago. Looks like something ate through the cement and burned. Nothing is stored on this part of floor and nothing was spilled. Very concerned. Any ideas?

On 2019-11-02 - by (mod) - What is the difference of painting or staining concrete slab that is inside the home?

Tomie thanks for a helpful question.

Painting a slab means applying a surface coat of some color and texture that adheres to the surface of the slab - as a sort of "skin" while staining a concrete slab means applying a liquid that carries pigment, but that actually penetrates the concrete surface. There's no skin to peel off.

The article above on this page discusses un-wanted discolorations or contamination on surfaces while

deliberately "staining concrete" to add a color or hue as you phrased it in your question is discussed separately:

at CONCRETE COLORING & POLISHING

On 2019-11-02 by Tomie Burdine

What is the difference of painting or staining concrete slab that is inside the home?

On 2019-11-02 by (mod) - Un-wanted "stains on concrete" versus how we stain (or paint) a concrete surface

Tomie thanks for a helpful question.

Painting a slab means applying a surface coat of some color and texture that adheres to the surface of the slab - as a sort of "skin" while staining a concrete slab means applying a liquid that carries pigment, but that actually penetrates the concrete surface. There's no skin to peel off.

The article above on this page discusses un-wanted stains or discolorations or contamination on concrete surfaces while

deliberately "staining concrete" to add a color or hue as you phrased it in your question is discussed separately:

at CONCRETE COLORING & POLISHING

On 2019-11-02 by Tomie Burdine

what is the difference of painting or staining concrete slab that is inside the hone.

On 2019-08-30 by (mod) - diagnose black & green stains on stamped concrete patio surface

Excellent thanks for clarifying that. It's certainly a convincing stamp;

More likely an algae than mold.

Watch out: if I'm right and that's algae, even though the stamped concrete has a textured surface it may still be very slippery when wet.

Details about just how slippery algae can be are found

at SLIPPERY STAIRS, WALKS, ROOFS

See STAMPED CONCRETE CLEANING for some cleaning advice

Also see our algae removal advice at

STONE, STUCCO & BRICK CLEANING METHODS

On 2019-08-29 by Brittany

It's concrete stamped with a stamp to look like wood.

Could you help identify these greenish stains on our patio?

Question: what are these red stains on our concrete basement floor?

The basement floor in our rent house has been painted grey.

These bright red stains keep appearing, they wash partly off but after short time reappear as before. Any idea what can be the cause? - Anonymous by private email 2019/05/26

Moderator reply:

On the off chance that this is a yeast fungus have you tried using a household bleaching type cleaner?

It would be good to First figure out what we've got causing those red stains otherwise we may not help and could even make matters worse

If bleach removes the stain it may indeed be a fungus.

Reader follow-up:

Have not, will try that tomorrow. I am thinking of getting some Zinsser Mold blocker primer.

...

A spray bleach solution seemed to take care of it and they haven't come back. This morning I painted the worst spots (will do all the rest tomorrow) with Zinnze

On 2019-01-17 by (mod) - identify stains on concrete concrete by physical sampling

CH

This is actually pretty easy to resolve.

Collect a tape sample from a particularly dark blotch and have it analyzed by a forensic lab. I suspect you're going to see that it's an algae bloom. If you confirm that, I can make some suggestions on reducing the problem.

On 2019-01-17 by coachhuebner

Driveway less than one year old. Whenever it rains black and dark spots come up from the concrete. The blotches take days to start to dry out while other driveways will be dry in a few hours.

Have had many concrete people look at it and have no explanation of how it could have occurred. Not mold or oil.

Plausible explanations - bad batch of concrete that had something in the mix, some type of chemical made its way onto the driveway and seeped into the porous concrete.

Everyone is unsure and have heard multiple time that they have never seen it before in all their years of concrete work.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-12-01 by (mod) -

Curtiss

That looks to me like oil stains, possibly from spills along the foundation wall; the lower white deposit may be efflorescence - search InspectApedia.com for EFFLORESENCE (OR to spell it correctly search for EFFLORESCENCE ) to read details.

Bleach won't remove oily deposits but other cleaners such as a garage floor cleaner are often effective.

On 2018-12-01 by Curtiss Wakefield

I have these stains on my concrete foundation. Bleach products have no effect. Do you have any idea what they are and how to get rid of them?

Thank you.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

 

On 2018-12-01 by (mod) - try garage floor cleaner on oily stains on concrete

Curtiss

That looks to me like oil stains, possibly from spills along the foundation wall; the lower white deposit may be efflorescence - search InspectApedia.com for EFFLORESCENCE to read details.

Bleach won't remove oily deposits but other cleaners such as a garage floor cleaner are often effective.

You posted the same question back in October of this year. I include that discussion below.

On 2018-12-01 by Curtiss Wakefield

I have these stains on my concrete foundation. [photo above]

Bleach products have no effect. Do you have any idea what they are and how to get rid of them?

Thank you.

On 2018-10-11 by (mod) - - try garage floor cleaner or de-greaser products on oily stains on concrete

Curtiss - in reply to your posting of the same questsion here and again in December:

I'm unsure what the brown stains are - perhaps deposits from the mud below, or if you know more about the site history you could rule in or out oils.

Bleach wouldn't be effective on soil, mud, nor oily deposits; it's an oxidant.

Jomax, similar to bleach, is a fungicide, incorrectly described as a "mildewcide" (mildew grows only on living plants). It's comprised of Acetic Acid, Surfactants, Water. In other words, vinegar. A good disinfectant but not effective against some staining materials.

I suggest trying a soap-based household cleaner and a scrub brush - maybe Simple Green or better, ACT, or CHOMP, concrete cleaners formulated to remove oil and grease stains from those surfaces.

The white deposits are probably mineral salts or efflorescence left by water against the foundation wall. Those are discussed at EFFLORESCENCE SALTS & WHITE DEPOSITS inspectapedia.com/Wet_Basements/Efflorescence-White.php

Let me know how this advice (and guessing) works for you.

On 2018-10-11 by Curtiss Wakefield

I have stains on my foundation which I cannot remove. I tried Jomax and bleach, RMR 86 and a pressure washer. I was hoping to identify the stain. I have included a picture.

Thanks

[Photo as shown at the start of this article]

On 2018-11-03 16:06:27.295372 by (mod) - diagnose red stains along concrete curb at property edge

I agree with investigating further as you describe;

Water in the soil picking up a stain material may seep to and collect along the concrete curb, spreading horizontally along that block, so the stain source may not be uniform in the soil;

OTOH the stain source could be more-uniform IF someone used contaminated soil as fill or even buried organic matter in the yard.

Attach photos of what you find.

You could also collect a sample of the liquid to have it examined by a forensic lab - in particular you'd care if it were petroleum, such as heating oil.

I also don't rule out a sewage line leak.

On 2018-11-03 by Jen

In the meantime, I'm going to get my metal detector out and see what I come up with.

On 2018-11-03 by Jen

I think there is something in the soil causing the stains which is why I am incline to dig up the grass

It would not surprise me to find some buried ( by the builder) scrap metal / rebar that would be causing this kind of rust stain, but all along the front of my house?

from one side of my property to the other? and I'm the only house that has this problem. Do you have a suggestion of who I might call? What would you do in my situation?

On 2018-11-03 by (mod) -

Do you think there's something in the soil that could be reducing the stain?

On 2018-11-02 by Anonymous

The yard itself is not upslope from the sidewalk to the street it is incline from the stop sign to where I'm standing taking the picture.this is along the whole front of my house this is only a small portion of the curb where I taken the picture to the mailbox my sidewalks and my driveway or not affected

Closer up of residue. two things I want to point out if you notice in the picture I sent you that includes the mailbox in the water meter you will see that the wetness starts at seam of the gutter. This mailbox in my house is a slight incline from the stop sign. Also. The residue appears as if it's dripping down from the ground above the concrete gutter from the grass area but it also has come up from the seam in the gutter. I hope I'm making sense

Pic of oily residue - shown above - .I will say that this residue whatever it is only appears after it has rained very hard. I live in Lithia Florida. The Ground by the mailbox/ water meter always feel spongy

Thank you for your prompt response. I have lived here for 3 years. Discolorations were unremarkable when I moved in previous owners might've just cleaned the concrete gutter/curb. The house is 5 years old. There is nothing buried that I know of no oil tank or vent pipe, but I might have to dig up the grass to find out.

This is my front yard, you can see the mailbox and between the mailbox and the sidewalk is the water meter and the neighbor's driveway.

I wish I could attach more than one picture I have some of the oily residue I will post a separate comment for you to look at.

When we moved in, There was nothing visible, no ruts in the yard, grass was intact, no heavy machinery or autos, no construction or inclement weather. This picture was taken in August.

On 2018-11-02 by (mod) - discussing red stains along concrete curb in Lithia Florida

Jen

What's buried along the curb or in the yard up-slope from the stains?

You say it's oily: is there a buried oil fill/vent pipe or oil tank ?

Where is the property?

What is it s age?

When did the stains first appear?

What conditions were present just prior to the occurrence? Weather, driving on the lawn, construction, modification, deliveries, treatments?

On 2018-11-02 by Jen--- help!!!

I have these brown stains all along the curb/gutter along the front of my house. I had water company come out and look because there was an oily residue and it is bubbling up from the seams of the gutter.

But they said there were no leaks. This picture shows a completely dry Street and gutter but it starts leaking at that particular seem it had not rained in days.

The stains however appear to come from a the grass that is adjacent to the curb. I have removed the stains with pressure washing and scrubbing acid. But they return. I don't believe it's my lawn spraying Company because my sidewalks and driveway and all of my other neighbors remain unaffected.

The main water valve is in the ground right next to the mailboxes. I'm at my wits end. it makes my house look extremely grungy. I am the only house on the street with this problem I don't know who to call

and aside from digging it up to see what's under there, I don't know what else to do. I have other pictures but I can only post one here. Any advice or suggestions you may have, I am grateful to hear.

On 2018-10-23 by (mod) - possible pour of oil across concrete before sealing

Andrew I'm not sure what caused the ark line in your photo, but often I've seen that sort of "stain" when a dribble of oil, cleaner, or something else was spilled across concrete.

The line appears later when a coating or sealant is applied to the whole surface, probably because of a difference in absorption of the coating into the concrete, or possibly because of a chemical reaction between the spill and the coating.

On 2018-10-23 by Andrew

These appeared days after sealing of the exposed concretw

On 2018-05-12 by (mod) - Terra etch

CS

Terra etch appears to be so common term that I did not find a single concrere treatment product of that name.

Generally concrete etching is an acidic or other concrete surface chemical treatment used to remove light stains and sometimes to prepare the surface for bonding of another coating, staining agent, or layer of material.

On 2018-05-11 by csoliven

Pool contractor laid color cement on a rainy day which resulted in a pink surface. The color was to be Omaha Tan.

Now they want to Terra Etch the concrete to try and remove the pink surface. What is Terra Etch and how does it affect concrete? What additional steps should be taken or is there any maintenance required?

They said the cement supplier feels moisture may be entrapped after 30 days and want to try Terra Etch before redoing concrete.

I don't understand how the moisture can be entrapped on the entire job. This doesn't make sense. Please help and educate me. thank you..

On 2018-02-15 by (mod) - rectangular marks on concrete may be due to forms or form ties

How interesting. I tried to zoom in for a closer look but unfortunately at magnification the photo is a bit blurry.

I can only assume that these are taking the marks are related to the forms or form release tabs that were used to pour this concrete shape.

Do you have any photos of the actual concrete forms of both sides of them?

On 2018-02-15 by Jane

These newly completed board formed concrete walls have strange rectangular markings? Any idea what might have cause this?

On 2017-11-08 by Eugene

Auto scrub concrete floor but after a day staining along saw cuts

...

Continue reading at CONCRETE STAINS: ID & REMOVAL or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CONCRETE COLORING & POLISHING
• STAIN DIAGNOSIS on BUILDING EXTERIORS - home
• STAINS on STONE, STUCCO DIAGNOSE & CURE - cleaning methods
• STAMPED CONCRETE CLEANING

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CONCRETE STAIN CAUSE & CURE FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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