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Stains in pattern on concrete slab floor © Daniel FriedmanStains on Concrete
Types & sources of stains on concrete surfaces & stain removal

Un-wanted stains & colors or discoloration & defects on concrete surfaces:

This article 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.

Methods for removing un-wanted discoloration or stains from concrete. Catalog of research on causes & cures of concrete staining. Concrete stain products & product sources are also provided.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

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

Colored stains and effloresence on a concrete wall, Queretaro, Mexico (C) Daniel FriedmanCatalog Of Sources of Concrete Colors, Marks, Stains & Staining or Discoloration

[Click to enlarge any image]

Before reviewing the types and causes of stains, discoloration, or defects in concrete surfaces, did you intend to read about how we deliberately color or stain concrete?

If so, see CONCRETE COLORING & POLISHING - how color is applied to concrete floors & other surfaces. Else please continue below.

Watch out: in order to have a chance of success at removing stains or discoloration on or in concrete, it is important to first make a best-effort to identify the type of stain or its source. As you'll read in the detailed concrete stain removal guides found on this page, the stain removal treatment that will work depends on the chemistry or cause or source of the stain on concrete.

Stains on concrete sidewalks, porches, or interior concrete floors may be ascribed to a variety of sources that we list here. We categorize concrete stains and discolorations in these groups:

Black-brown stains on concrete floor (C) InspectApedia.com Noah

The concrete floor staining above is discussed

at CONCRETE STAINS, BLACK, BROWN, TAN where we show more photos of this interior concrete floor.

Concrete floor with stains where asphalt asbestos or vinyl asbestos floor tiles and their adhesive mastic were removed (C) InspectApedia

Red rust stains on a concrete sidewalk Vassar College Poughkeepsie NY (C) Daniel Friedman at InspectApedia.com

Hard finished gray stained concrete interior floor slab (C) Daniel Friedman Ralph Arlyck

Below: the concrete floor was "stained" using an acid treatment. The light patches in the left of the photo indicate foot-traffic wear through the acid-treated concrete surface . (Rigby 2006).

Acid stained interior concrete floor (C) Daniel Friedman

Wear on a stained concrete floor will be increased by any of the following

Effloresence white stains on concrete wall around form tie leaks (C) Daniel Friedman

See these diagnostic articles

Dark Stains on Concrete: chronic moisture

Reader Question: what are these black stains on our concrete porch?

Dark stains along concrete slab exterior porch perimeter (C) InspectAPedia Rhonda

4/1/2014 AUTHOR:Rhonda (no email)

COMMENT: I have a problem with my front porch, it runs the whole length of the porch, tried pressure washing it, it didn't come off and seemed to make it worse.

Reply:

Rhonda, the black marks in your photo (shown here so that others may comment) may be due to moisture variations in the slab, moisture from below, or moisture entering the house-slab juncture, possibly bearing staining contaminants.

But most likely we're looking at a combination of variation in concrete hardness and moisture level.

The observation of those round-ish blot stains on the concrete slab surface in front of the entry door suggest that a door mat was placed there previously, holding moisture in the slab (possibly during curing). Does the stain pattern vary with dry weather?

This comment was originally posted at MOLD APPEARANCE - STUFF THAT IS NOT MOLD

Stains on New Concrete Drive May be due to Concrete Additive

The stained area at this concrete drive entry were ultimately traced to possible inadequate mix of a cold-weather accelerator (CaCl) added to the concrete during concrete placement.

Poor surface and mixed red stains on concrete drive may be due to poor mix of additive during cold weather (C) InspectApedia.com Paul

A detailed discussion of the history, diagnosis, and final concrete contractor repair proposal are found

at EFFLORESCENCE & BROWN DEPOSITS

Research References: Stains & Stain Removal Methods on Concrete Surfaces

Causes Of & Cures For Stains on concrete: diagnosis & removal of stains & discoloration

Watch out: some of the cleaners, poultices and other methods described for removing stains from concrete involve dangerous chemicals.

Do not attempt to follow those procedures if you are not properly equipped with personal protective equipment, have protected surrounding materials from damage, and are trained in safe or professional procedures for handling these chemicals and cleaners.

Stains on concrete - Gaudette NPS cited & discussed at InspectApedia.com

Research on Concrete Stains & on Air Entrainment in concrete & freeze-thaw effects

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-06-15 by InspectApedia-911 (mod)

@Kerry,

Thanks for the update; post photos of what you find so that we can take a look, too.

On 2022-06-15 by Kerry

@InspectApedia-911, thanks! I was leaning towards 3 when I my neighbour offered me some Wet and Forget. I tried it on a small patch and it’s turning a little orange indicating a reaction of some sort. I did it in the same area where I tried oxy powder which did brighten a small area. I still have hope.

On 2022-06-14 by InspectApedia-911 (mod) - options for concrete driveway discoloration

@Kerry,

Those dark areas look as if they may be an artifact of the concrete pour, such as surfacing of concrete additives used in the concrete at the time it was placed, possibly surfacing under plastic that was laid down over the fresh concrete as it cured.

Options - all cosmetic - include

1. test more-aggressive surface cleaning in an unobtrusive and small area, such as using a muriatic acid based cleaner.
Watch out: there are safety hazards - read instructions and follow them with care.

2. apply a concrete coloring stain

3. live with it.

Collingwood Ontario discolored concrete driveway (C) InspectApedia.com Kerry

On 2022-06-14 by Kerry

@InspectApedia-911, I wish I knew. We are second owners. I’ve asked the builder/first owner for info. We are in Collingwood Ontario near Georgian Bay so it does get a fair bit of snow.

There are dark spots in the brush finished area and on the smooth border as well. I can take another photo.

On 2022-06-14 by InspectApedia-911 (mod)

@Kerry,

How soon after the concrete was placed did these discolorations appear?

What's your climate?

Is there a surface texture difference in and out of the "stain" areas?

On 2022-06-14 by Kerry

I have no idea what caused these marks on our concrete steps but no amount of pressure washing or scrubbing will brighten it.

I’ve tried all non chemical options and can get the underlying concrete brighter with tons of scrubbing but the drop marks stick around. The house is roughly 3 years old.

Collingwood Ontario discolored concrete driveway (C) InspectApedia.com Kerry ... Collingwood Ontario discolored concrete driveway (C) InspectApedia.com Kerry

On 2022-04-27 by Inspectapedia Com Moderator - orange staining on pool deck under pool tarp

@Angela,

Thanks for a tough question that is helpful to consider.

I don't know the answer - lacking objective facts - but I speculate that chlorine in the pool water may have bleached the concrete near the pool edges, perhaps influenced by longer retention of moisture where the pool cover extended over the pool edges.

(Chlorine is a bleaching agent.)

I'm doubtful that you can wash off the light color though of course using plain clean water won't hurt a thing.

I'd hold off on a sealer - I don't want to make matters worse by a coating that might have the effect of retarding the fading together of various colors to a more-common hue.

On 2022-04-26 by Angela

My pool deck in south East PA. Concrete was poured in Sept of 2020 and now this spring we are seeing this orangey mottling coming up, particularly where the pool cover overlapped. The cover is mesh and dark green color. We did not see this last year.

When installed we asked for the cement to be whiter in color compared to the more grey standard and they said they achieved this by adding a higher proportion of cement to the mix. Questions are, could the whiter mix be the reason for this? What else could it be?

We live in a very wet climate. Could it be a structural concern?

Cement doesn’t show cracks or flaking as of now. Should we try to wash it off and seal it? Thanks!

Orange staining on pool deck in east PA (C) InspectApedia.com Angela

On 2022-04-22 by Inspectapedia Com Moderator

@Norma Cook,

It would be helpful if you could post a photo of the stained area and also post in a second comment and second photo the nature of the mat that was placed there. I like to know the mat's constituents and its brand.

On 2022-04-22 by Norma Cook

About a week after our new porch was poured, an orange color came up. It was under the porch mat and I wouldn't have noticed but they laid the mat up to the step instead of the door.

My husband wouldn't call back the man that poured it, saying it would probably go away. Not only is it still there but more of the stain is showing up on more of the porch.

It's about 25% covered with this stain. I tried CLR but it didn't do anything to the stain. I have spent over $12,000.00 to make the front of my home look nice but when you walk up to the porch and see that stain, it spoils it.

On 2022-06-07 by InspectApedia-911 (mod) - concrete form oil to prevent sticking of concrete forms

@Anonymous,

Adding an example for Concrete Form Oil in Australia (see if you can find out what product was used on your concrete and let us know)

Royal Concrete Form Work, 6 - 14 Cosgrove Road Strathfield South NSW 2136 Sydney Tel: (02) 9642 2200 - other offices in Melbourne and Brisbane, Web: https://formworksolutions.com.au/

FORM RELEASE OIL Excerpt:

ROYAL Mould oil is a bond-preventing formwork release agent applied as a thin coating to formwork prior to concrete pour to prevent sticking or concrete build-up and to ensure clean stripping.

This results in minimum cleaning, and instant re-use. It protects wooden forms/ formply from water and alkalis, preventing grain raising and breakdown of wood fibres, thus extending useful life. Applied by fine spray or applied by brush, or cloth.

Shown here CR Form Concrete Mould Release

On 2022-06-07 by InspectApedia-911 (mod)

@Anonymous,

Thanks that's a helpful photo of concrete pour forms.

Consider that the forms are often coated (inner surface) with a release agent that makes it easier to pull the forms off of the concrete after the concrete has been placed, set, and cured enough.

Sometimes the release agent may leave stains or marks on the concrete too.

If the stains are a release agent, those are in essence an type of oil that can often be scrubbed off using a simple mix of dish detergent and water and a soft bristle brush. Don't try scrubbing new concrete before it's sufficiently hard as you could scuff up the surface.

Test some detergent scrubbing on a small unobtrusive area first.

There is a wide range of concrete form release agents and oils, some are water-based and are easier to clean-off.

Below we show just one example of many, from WR Meadows, a supplier of concrete form release agents.

See this

On 2022-06-07 by Anonymous

@Inspectapedia Com Moderator, The black staining does not come off with a clean paper towel or dry paper towel.

Concrete forms photo attached. Interestingly at another area on the same project, same process was used for formwork and stripping and the discolouration is no-where near as noticeable.

We believe this puts it down to two causes - time of the year it was poured, Darker stained area was December (summer in australia) while the lighter colour was australian winter.

Australia concrete forms (C) InspectApedia.com Anon

On 2022-04-02 by Inspectapedia Com Moderator - using CLR is a Calcium-Lime-Rust remover on concrete stains

@Anonymous,

CLR is a Calcium-Lime-Rust remover. It's suitable for removing efflorescence: typically white stains and salts left behind from evaporating water on concrete or other masonry surfaces.

CLR is not likely to be the best choice for other types of concrete stains but certainly won't hurt the concrete if you want to give it a shot.

Muriatic acid and other acid cleaners are often used to remove concrete stains but must be used with great care to follow the manufacturer's instructions - acids are innately hazardous chemicals.

I'd like to know what that black staining actually is. Can you wipe it off at all using a clean dry paper towel? Or a wet paper towel? Let me know.

Above on this page we describe "black stains on concrete" that are not actually stains (from some external material or source) but may be moisture variations in the concrete.

So let's first understand more about what's on or in our concrete wall.

And also post photos, if you can, of the concrete forms used and find out what release agent was used to coat the form surfaces before the concrete was placed.

On 2022-04-02 by Anonymous

Hello,
Formwork has been left on for >14 days and the attached staining has appeared on concrete.

What is it and how can I get rid of it. Brand new plywood was used. I have read online potentially the use of CLR, acids etc?

Australia concrete forms (C) InspectApedia.com Anon

On 2021-12-21 by Inspectapedia Com Moderator - efflorescence under carpet on concrete

@Mel,

That white powdery material is probably efflorescence

detailed at EFFLORESCENCE SALTS & WHITE DEPOSITS

Those dark straight-lined marks that seem to taper to a fading point are man-made, perhaps during construction as locator marks, and have nothing obvious to do with water entry (unless they point to a cut or hole or fastener location that might have made a perforation in the concrete).

On 2021-12-21 by Mel

We recently found a random wet area in our carpet in the dead center of our room with no leads to where it came from.

Even the plumber we called wasn't sure. My husband and I ripped up the carpet to try to find the source and we found some strange marks on the concrete underneath as well as some mildew underneath the carpet padding.

It looks like someone previously worked here as there's all kinds of tape and such under the carpet padding.We are most curious about these weird cross hatch markings that look burned onto the floor. There's a few sets of prints like the one in the picture I attached. Thank you!

Efflorescence under carpet on concrete (C) InspecTapedia.com Mel

On 2021-10-29 by (mod) - orange stains on concrete may be from rebar

@Josh,

Sure, there could have been rust lines from re-bar that traveled under the plastic, a plausible explanation.

To test that, try an iron-stain remover on a small area of one of the stains and let us know what happens.

The clay stains are a second possibility, though perhaps less likely if the plastic was new and if there wasn't red clay dust atop the new pour nor on the plastic just prior to rain.

At STAINS on BRICK SURFACES

we include an example of using an iron stain remover

On 2021-10-29 by Josh

@inspectapedia.com.moderator,

Thanks for the reply! This is showing up on a driveway and walkway pavers that we had poured, so will definitely be noticeable. We do have heavy clay in the the soil (Houston), and I was told the plastic was new but can't confirm.

They used rebar to hold down the plastic, but it was on the sides on top of the plastic, not directly laying on the concrete. Could rust have travelled along the plastic that contacted the ground? Have added another picture that may show a bit more of the site.

Orange Concrete Stains (C) Inspectapedia Josh

On 2021-10-28 by (mod)

@Josh,

If the concrete is to be covered with a finish surface such as tile or flooring, then those stains don't need to be removed.

With no information about your site or about possible contaminants it may have been on the covering plastic we can but guess as follows:

I haven't seen that exact combination of concrete stain color and pattern before.

But their linear nature could map areas where there were wrinkles in the covering plastic; such wrinkles in plastic over new concrete might collect or hold extra surface water in rainy weather, and if surface runoff included mud or fine soil particles (or other contaminants) that guess might be accurate.

Is there clay soil at and around your site?

Was the plastic covering new or had been used elsewhere before?

Before using an acid wash on the concrete, consider that any concrete discoloring or stain removal will be more effective if we correctly diagnose the cause of the stain or its constituents.

When the concrete has cured sufficiently that scrubbing won't damage its hardened surface, then try detergent and water, and you might try using an iron stain removing product.

Test on a small area of stain before going to the trouble of buying a lot of cleaning chemical or making a mess.

Keep us posted.

On 2021-10-27 by Josh

I had a pour done on Saturday. Light rain for about 15 minutes at the end of the pour, with 5 minutes of heavy rain. The contractors put plastic over the concrete and orange streaks have appeared after it has dried for a few days. The below pic was taken today (Wed). No one seems to know what caused this and are recommending an acid wash once it has cured for a couple of weeks. Has anyone on this board seen this before, have any recommendations?

Orange Concrete Stains (C) Inspectapedia Josh

On 2021-09-07 by (mod)

@Anonymous,

I'm not sure what we're debating here under the aegis of me trying to help you.

As you've never heard of applying stains to concrete deliberately, you may want to

see CONCRETE COLORING & POLISHING - how color is applied to concrete floors & other surfaces - where we describe that process.

My suggestion is that you're not likely to find a sufficiently close match to the reset of the concrete that such coloring is worth the trouble and cost. I named it for completeness.

Bottom line:

If as it appears you've lost the very top surface of the concrete then no further etching, cleaning, scrubbing, etc. is going to make it look like it used-to - or like the surrounding, intact concrete surface.

On 2021-09-07 by Anonymous

@inspectapedia.com.moderator,

In your last reply, you said, "there are, however, etching processes as well as bonding agents that might let you then try to coat the surface with portland or cement..."

Sorry, but I have no idea what you're talking about.

One can try applying to the slab an acid stain, a water based dye, or a pigmented sealer. These likely though will highlight the marks more than anything and not mask the spots.

In a earlier reply you said,
"There are cosmetic steps that might make that area look a little better, but in my opinion rather iffy, such as finding a concrete coating ...."

The only way to make the slab look cosmetically better to which you said would be "iffy", is to apply a micro-topping to start out new. I never heard of anyone ever applying stain, dye or adding a pigmented sealer before installing a microtopping. But that's what apparently it sounds like you stated if you read your entire reply.

On 2021-08-31 by (mod) - surface of concrete lost

@Jess,

It looks to me as if you've lost the high-portland-content skim coat that was on the surface of your concrete;

It's your concrete, and of course I'll be grateful to learn the results of any further experiments you try - that will help other readers.

But I'm doubtful that any further treatments that remove surface material will restore what has been lost; there are, however, etching processes as well as bonding agents that might let you then try to coat the surface with portland or cement that comes closer to the original color.

At the end of the day we're left with what is principally a cosmetic concern.

It looks as if wear from the furniture wheel has removed some of the concrete surface, leaving a darker substrate.

On 2021-08-31 by Jess

@inspectapedia.com.moderator,

Hello again. I apologize for asking this question. But Is it possible that an application of 1.65% alkyl dimethyl benzyl ammonium chloride (Benzalkonium) could further cause more surface etching? In my estimation, this may be only option remaining to see whether I can lighten the darkened spots, at this stage.

Thank you in advance.

On 2021-08-31 by Jess

@inspectapedia.com.moderator,

I attached a closer photo along the edge of stain. the aggregate

This close-up along the side of the stain and the unaffected concrete does reveal some of the aggregate where the top most layer was removed. I wouldn't go so far as to say the entire surface area is etched as much as those areas revealing the aggregate.

For instance, the darkest discolored spots don't appear to have any surface removed.

(They do feel smoother than the untreated concrete, however. But basing the appearance of this photo to how it visually appeared last year to the naked eye, the darkest spots made up the entire stained area prior to the successful attempts to lighten it in 2020.

So I not completely convinced the darkest discolorations can't be lightened. The question is then how to accomplish that at this point without causing additional etching.

Black Concrete Stain (C) Inspectapedia Jess ...

On 2021-08-31 by (mod)

@Jess,

One thought occurs to me that you might want to test.

It is possible that all of that cleaning in the stained-area, combined with the effects on the area of the original planter that sat there, actually has removed some of the original concrete surface - lighter colored material - leaving a darker, more-coarse concrete surface exposed.

Try taking a close-up macro type photo, very sharp and well lit, showing the edges of the stained area - and maybe try again with a magnifying glass.

That may tell us if I'm right.

If so, no amount of additional cleaning will make the stain go away, because it's not a stain, its lost surface material.

There are cosmetic steps that might make that area look a little better, but in my opinion rather iffy, such as finding a concrete coating or paint that's as close to the original surface as possible, or worse, painting the whole area - not something I'd recommend.

On 2021-08-31 by Jess

Last year I placed two potted planters on unsealed concrete at the front door entrance. The minerals from the fertilized soil, and probably also the clay pots caused black stains. The pots were removed three to four weeks after they were initially set down.

I tried scrubbing the black stains with water, mild soap plus ammonia, water, mild soap plus vinegar, and finally with a concrete and asphalt driveway cleaner (ZEP brand). The stains became a grey permanent stain.

I couldn’t fully remove them. As a final step, I sprayed the stains with Wet n Forget and stopped attempting to remove the stains for the remainder of the year. By the end of the year there was a small change where the stain was becoming lighter.

This year, I wanted to see if I could lighten the stains even more. I began spraying the stains in May with Wet n Forget and sprayed them several times up until this late August. I saw little marked improvement during this time period. I occasionally watered the stains with a garden hose to aid in the process during the dry summer months.

The following mistakes are those made to cause the stains to become much, much worse:
In late August of this year, I sprayed a 50:50 solution of 6% vinegar and water on the stains keeping the stains wet for approx. an hour. After the application time and as the solution dried, I saw no improvement.

I did notice that the vinegar and water solution slightly surface etched the stained concrete areas. I then made the mistake of not rinsing the concrete that same day to remove all of the vinegar solution from continuing to etch the concrete.

I also went further by applying a 2 part water to one part oxygen bleach mixture (sodium carbonate and sodium percarbonate) right after applying the vinegar and water solution. I lightly scrubbed the bleach mixture with a nylon brush and allowed it to sit for approx. 10 minutes.

After I flooded the concrete to rinse off the oxygen bleach and let the concrete dry, the stains went from light gray to black. How can this have occurred? I hastily went so far as to make yet another mistake by spraying a mixture of swimming pool algae guard containing active ingredient 15% concentrate alkyl dimethyl benzyl ammonium chloride after flushing the oxygen bleach with a garden hose.

The swimming pool algae product (brand name ‘Algae Guard’ by HTH) does not contain pool chlorine. I realized 45 minutes after applying the algae guard that I had made a dilution error.

The solution was too highly concentrated and the miscalculation allowed for a 14%. solution. The Wet-n-Forget ‘ready-to-use’ product is 1.65% alkyl dimethyl benzyl ammonium chloride (Benzalkonium) which is what I was shooting for. (formula (V1 *C1 = V2 * C2). The idea was basically to try to manufacture a home made concoction of Wet n Forget

After applying the highly concentrated algae guard and after it was allowed to dry, the black stains had now spread out even farther than the original stains. I flooded the concrete with buckets of hot water and then applied a box of baking soda to make a paste.

I lightly massaged the thick paste by hand and a nylon brush onto the larger stains. After approx. an hour, I flushed with a garden hose.

The following day, the two stains became much worse than ever before.
I was only able to attach one photo of one of the stains.

I was hoping I could correct these errors I made so at least the dark stains could be made a lighter gray (as they were last year). Sorry, I don't have any photos of how the stains looked before these mistakes were made.

Regards, Jess P.S. I no longer own a power washer.

On 2021-02-10 by (mod)

I'm unsure, Todd,

Take a look at the common types of stains on concrete above;

Also look closely at the surface area of that dark spot: is the surface rough or spalled?

On 2021-02-10 by Todd K

Anyone know what this is? Covered patio. Slab is 12-14 Mo. old. Thanks!

Patio Concrete Mark (C) Inspectapedia Todd

Question: how do I get rid of these stains on my concrete floor?

Dark stains on concrete floor - identify & remove (C) InspectApedia.com JosephMike Joseph · Mar 2, 2021

I live in an apartment and trying to identify a concrete stain so that I can properly clean it. It looks like a resident spilled something and didn’t really clean it up.

The spill didn’t seem so bad initially (it was kind of light brownish at first), but the stain has become darker and more noticeable.

Can anyone identify what the source is? Trying to determine whether the source was a health hazard so that I can clean it up appropriately.

Moderator reply:

@Mike Joseph,

I can't tell from your photo what those dark stains are; we'd need a sharper, closer look plus some understanding of the history of what's been on or near that floor section.

But see the help offered at

CONCRETE STAINS: ID & REMOVALinspectapedia.com/exterior/Concrete_Stains.php

where we discuss how to identify and thus treat various types of stains on concrete.

Or you can always try the experimental approach, starting with the safest, most-harmless cleaners such as

- dish soap

- TSP substitute cleaner

- concrete garage slab and driveway cleaner products

- concrete cleaning acids such as Muriatic

Watch out: Muriatic acid s a dangerous chemical that requires special procedures and handling for personal safety

Question: pink "efflorescence" on garage floor slab

I see efflorescence on my concrete garage floor. I also see some pink material as well.

Pink stains on concrete: cause & cure (C) InspectApedia.com DeSario

Have you ever seen pink efflorescence? Or could it be mold? - Anonymous by private email 2019/09/22

Moderator reply:

Yes pink efflorescence salts (or red, brown, white, even green) can be deposited, depending on the composition of the masonry material that is suffering leakage or water exposure.

But there may be other sources of pink on a garage floor such as from antifreeze or transmission fluid leaks too, or even bacterial action on an organic spill.

Reader follow-up:

It is just regular poured concrete and I never noticed the pink before, just the white efflorescence. So probably not mold?

Moderator reply:

I can't say for sure from just a sort-of blurry photo; there are red or pink molds and yeasts, and there are molds that will grow on just about anything, including perhaps dirty or dusty concrete walls;

Let's follow the water first.

On 2020-07-10 - by (mod) - diagnose & cure dark mottled, blotchy, or water run-down stains on interior concrete wall

Dark blotchy mottled stains on smooth indoor concrete wall (C) InspectApedia.com JaniceJanice

I agree that the stains on your concrete walls may be an artifact from original forms work and construction. If so they're not harmful and are only a cosmetic issue.

You will see other examples of similar un-invited stains on concrete

at CONCRETE STAINS: ID & REMOVAL where I will post and hope we can continue this discussion.

As with many building and environmental questions, we will have better success if we understand the problem before posting a solution.

FIRST:

Let's be sure we're correct about the wall materials and that we understand how, when and how it was constructed. .

Is this wall really solid poured concrete?

Is this wall plaster on a wood or steel-framed cavity wall?

Is this wall cement board or plastered gypsum board on a cavity wall or over a masonry wall?

What is the type of construction of the building.

Where is the building: country and city?

What is the building age?

What is the building's leak history?

SECOND:

Dark mottled and rivulet or down-run stains on a concrete wall may be due to water intrusion or water condensation or even an artifact of the concrete pour and the forms used.

Some discolorations in concrete, including dark areas, are natural, not harmful, and are not economical, if even possible, to remove.

If the owner has cleaned the wall surface there's not likely to be mold on that surface.

If stains are embedded in the wall they're probably not going to be removed.

Some of the wall stains in your photos look like water tracking down the wall.

If there is water entry through the wall the source needs to be found and fixed.

When the wall is dry, not leaking, and stable, if you object to its colors and appearance it can be painted or stained with a product designed for use on concrete.

On 2020-07-10 by Janice

Water run-down stains on interior concretre wall (C) InspectApedia.com JaniceHow would you go on to remove these stains or molds?

Is it possible to remove them without professional help in your opinion? The owner cleaned the area with H2O2 cleaner, but didn't remove the mold properly before. Is bleach and or TSP adivsible?

Thank you for your previous answer!

Also, I saw pegs sticking out the wall now, they probably got pushed out by moisture, since they were not visible before and were under paint/ concrete. I don't know a whole lot on construction work.

Might this be from construction for pouring the concrete or could that be a professional mold cleaning procedure from a previous attempt of removing molds in this appartment?

Or those are just pegs from holding something in the wall. (see photo, black spots are pegs with darker stain around them)

These stripes in the previous picture seem that liquid was dripping down, i think this damage was done by too much humidity without venting, but it might also come from outside?

I advised that the resident should contact the landlord, but she is afraid of the cost implications that this will produce, since most likely she will be held accountable at least to some degree because of insufficient venting.

Dark mottled stains and nail or other pops in interor concrete wall (C) InspectApedia.com Janice

Reader Question: what are the different concrete stains & markings shown in these photographs?

Please offer me your expert opinion on what is going on with my structural walls. I am working on a project located on Eko Atlantic Lagos Nigeria. And despite all our efforts we keep getting bug holes as shown below. C.I., Nigeria, 7/2/2014

Reply: a catalog of concrete surface markings & stains

I'll be glad to try to assist, with the warning that I am not a concrete engineer, though I do have experience in the subject.

Commenting on your photos in order [Click to enlarge any image]

Air bubbles pockets bug holes in concrete poured wall, Nigeria (C) InspectAPedia CI

1. Your photograph of "bug holes" in the concrete wall photo above look to me like small voids due to air bubbles in the concrete pour, probably due to poor mixing;

On larger & commercial concrete placement projects concrete contractors use a vibrator to remove these bubbles and avoid the voids.

In my photograph below, taken at the Vassar College building project in New York in 2014 you can see workers using the vibration tool as a large floor slab is being poured.

Using portable vibrators in concrete during a large concrete slab placement, Vassar College, Poughkeepsie NY 2013 (C) Daniel Friedman

Only if these "bug holes" are in very great number would one expect there to be a structural concern. I can't evaluate that from a photo - you'd need an onsite expert. Usually for an important pour of structural concrete an expert checks the mix and the slump and the placement of reinforcing steel.

It's worth noting that entrained air has been intentionally included in some concrete placement operations for a very long time as a partial protection against freezing effects, salt scaling and other forces, as described in these research citations where proper air entrainment procedures are explained.

As you'll see in our citations given below, Powers (1969) has written extensively on this topic.

Holes & chip marks in a vertical concrete wall (C) InspectAPedia CI

2.Photograph of holes & chip marks in a concrete wall (above) looks like chipping or spalling where concrete form ties were removed (cosmetic)

Dark parallel horizontal lines in a newly placed concrete wall (C) InspectAPedia CI

3. Photograph of the dark horizontal lines in a concrete wall (photo above) look like concrete form ties; the horizontal lines seem to mark boards used for the concrete forms

. I suspect that moisture variations during wall curing or possibly accumulation of water in irregularities in the form-wall caused the darkness.

The rippled surface in the lower right corner of the photo above (enlarged just below) suggests the mix contained excessive water or that plastic had been placed against the inner surface of the concrete form, but that's just an OPINION and we'll be interested to see what some of our readers who are concrete experts can offer.

Concrete wall ripples (C) InspectAPedia CI

4. & 5. Photographs of dark lines and blotchy areas in the concrete walls in the two photographs below look like cold pour joints in the concrete wall.

Dark areas suggesting cold pour joints in a concrete wall (C) InspectAPedia CI

In your last photo (below left) we see both cold pour joints and rough surface areas or surface voids in the poured wall as well as holes (in both photos) from form ties.

Concrete Stains from Rusting Inclusions or Exfoliating Steel

The lower photo also includes reddish stains that may be rust from either metal forms or from iron slag inclusions in the concrete mix.

Dark areas suggesting cold pour joints in a concrete wall (C) InspectAPedia CI

See details about cold pour joints found

at CONCRETE COLD POUR JOINTS

If you give permission for me to publish these photos I may be able to solicit more expert opinions for you - I can keep your identity information private or can publish it with your contact information - which ever you prefer.- DF

Reader follow-up:

You reflected my thoughts as well. Thanks for the link on concrete cold pour joints it was insightful.

You have my permission to publish these photos though I think your observation is spot on.
And I look forward to reading what anyone else has to say.

Below are a concrete batch report and a sketch of the concrete wall plan for our project.

Batch report of concrete mix (C) InspectApedia CI

[Click to enlarge any image]

Concrete wall plan schematic (C) InspectApedia CI


...

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