Stains in pattern on concrete slab floor © Daniel Friedman Stains on Concrete
Identification of types & sources of stains on concrete surfaces, accidental or deliberate concrete staining & stain application or stain removal

  • CONCRETE STAINS - CONTENTS: 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.
  • POST a QUESTION or READ FAQs about stains found on concrete surfaces: walls, floors, ceilings
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Stains & colors or discoloration 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.

Green links show where you are. © Copyright 2015, All Rights Reserved.

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]
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:

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

  • Concrete stains associated with spills or leaks, such as a sewage backup or oil spill, even spilling of a cleaner or other chemical or solvent. The stains shown in our photo at left (a restaurant in Poughkeepsie, NY, USA) are characteristic of vinyl-asbestos or asphalt asbestos floor tile mastic or adhesive that was removed during building renovation. The concrete was cleaned, polished, and coated with a clear sealant.
  • Concrete stains associated with bleed-through of substances from other sources such as contaminants outside a foundation wall, insulating or expansion joint materials at the perimeter of a slab,oil leaks from an outdoor oil storage tank or vehicle.
  • Concrete stains associated with rusting iron or steel or slag steel inclusions in the concrete material, either by deliberate inclusion as reinforcement, or by accident such as stones or scrap containing iron that are later exposed to water and possibly freezing cycles.
  • Concrete stains on painted concrete surfaces, such as mold growth on painted concrete; mold may also grow even on bare concrete where organic dust and debris have accumulated (dogs living in the un-finished basement). See Mold on Concrete, Stone, or Masonry Surfaces
  • Deliberate stains or colors applied to concrete floor slabs as a finish treatment using acid treatments or paint-on stain colours. At below left the variations in gray color of the interior hard-finished floor are within normal occurrence on a hard-finished concrete floor slab of this Tivoli, New York home.

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

At above right 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).

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

    • Foot traffic, especially if there is grit tracked onto or present on the stained concrete floor surface
    • Wear caused by hard wheels on office chairs, library carts, trolleys, or other rolling equipment
    • Moisture penetrating the concrete floor from below
    • Moisture left atop the sealed floor
    • Spills of solvents or acids that damage the protective coating
    • Poor original concrete mix or placement or excessive water in the pour that yields a soft, spalling surface

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

  • Concrete stains associated with moisture such as foundation leaks or moisture below floor slabs.

    Even if we do not see actual water on the concrete floor or slab surface, variations in moisture sources below the slab can create dark areas of higher moisture.

    The white and gray stains shown on the poured concrete basement wall at left are due to water and moisture seeping through the wall at concrete form ties that were not adequately sealed on the wall exterior after initial construction.


See these diagnostic articles

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.


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

Research References on Stains on Concrete Surfaces

Causes of stains on concrete; diagnosis & removal of concrete stains & discoloration

  • Anastasiou, E., and I. Papayianni. "Criteria for the use of steel slag aggregates in concrete." In Measuring, Monitoring and Modeling Concrete Properties, pp. 419-426. Springer Netherlands, 2006.
  • Broomfield, John P. Corrosion of steel in concrete: understanding, investigation and repair. CRC Press, 2002.
  • Chew, Michael YL, and Phay Ping Tan. Staining of facades. Singapore: World Scientific, 2003.
  • De Muynck, Willem, Anibal Maury Ramirez, Nele De Belie, and Willy Verstraete. "Evaluation of strategies to prevent algal fouling on white architectural and cellular concrete." International Biodeterioration & Biodegradation 63, no. 6 (2009): 679-689.
  • Dubosc, A., G. Escadeillas, and P. J. Blanc. "Characterization of biological stains on external concrete walls and influence of concrete as underlying material." Cement and Concrete Research 31, no. 11 (2001): 1613-1617.
  • Escadeillas, Gilles, Alexandra Bertron, Erick Ringot, Philippe J. Blanc, and Arnaud Dubosc. "Accelerated testing of biological stain growth on external concrete walls. Part 2: Quantification of growths." Materials and structures 42, no. 7 (2009): 937-945.
  • Escadeillas, Gilles, Alexandra Bertron, Philippe Blanc, and Arnaud Dubosc. "Accelerated testing of biological stain growth on external concrete walls. Part 1: Development of the growth tests." Materials and structures 40, no. 10 (2007): 1061-1071.
  • Harrison, D. "The Removal of Stains from Concrete." Ontario Hydro Research News (1959): 19-24.
  • Higgins, D. D. Removal of stains and growths from concrete. No. Monograph. 1982.
  • Hurd, M. K. "Cleaning concrete." Concrete Construction 37, no. 11 (1992): 791.
  • Kosmatka, Steve. Discoloration of Concrete, Causes and Remedies. Concrete Products, April, 1987.
  • Kuenning, WH, Removing stains from concrete. Aberdeen Group, 1993.
  • Kuenning, W. "Methods of removing some specific stains from concrete: Oil to Wood." [PDF]
  • Mindess, Sidney, and James C. Gilley. "The staining of concrete by an alkali—Aggregate reaction." Cement and Concrete Research 3, no. 6 (1973): 821-828.
  • Ramachandran, Vangipuram Seshachar, and J. Beaudoin. "Removal of stains from concrete surfaces." Canadian Building Digest (1973): 1-4.
  • de Rincón, O. TROCONIS, A. ROMERO de Carruyo, D. Romero, and E. Cuica. "Evaluation of the effect of oxidation products of aluminum sacrificial anodes in reinforced concrete structures." Corrosion 48, no. 11 (1992): 960-967.
  • Uemoto, T. "Maintenance of concrete structure and application of non-destructive inspection in Japan." Proc. Non Destructive testing in Civil Eng (2000): 1-11.

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

Research citations on air entrainment in concrete & freeze-thaw effects

  • Cordon, William A. "Freezing and thawing of concrete-mechanisms and control." (1966).
  • A Symposium. "Entrained Air in Concrete." In ACI Journal Proceedings, vol. 42, no. 6. ACI, 1946.
  • Gokce, A., S. Nagataki, T. Saeki, and M. Hisada. "Freezing and thawing resistance of air-entrained concrete incorporating recycled coarse aggregate: The role of air content in demolished concrete." Cement and Concrete Research 34, no. 5 (2004): 799-806.
  • Pigeon, Michel, and Richard Pleau. Durability of concrete in cold climates. CRC Press, 2010.
  • Powers, Treval Clifford. "The properties of fresh concrete." (1969).
  • Powers, Treval Clifford. "Void space as a basis for producing air-entrained concrete." In ACI Journal proceedings, vol. 50, no. 5. ACI, 1954.
  • Powers, Treval Clifford, and R. A. Helmuth. "Theory of volume changes in hardened portland-cement paste during freezing." In Highway research board proceedings, vol. 32. 1953.
  • Powers, Treval Clifford, and T. F. Willis. "The air requirement of frost resistant concrete." In Highway Research Board Proceedings, vol. 29. 1950.
  • Verbeck, George J., and Paul Klieger. "Studies of'salt'scaling of concrete." Highway Research Board Bulletin 150 (1957).
  • Whiting, David, and David Stark. "Control of air content in concrete." NCHRP report 258 (1983).
  • Wright, Peter Joseph Frederick. "ENTRAINED AIR IN CONCRETE." In ICE Proceedings, vol. 2, no. 3, pp. 337-358. Thomas Telford, 1953.



Continue reading at STAIN DIAGNOSIS on BUILDING EXTERIORS or select a topic from the More Reading links or topic ARTICLE INDEX shown below.


Suggested citation for this web page

STAINS on CONCRETE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References

Support & See Fewer Advertisements

From Google's Contributor website: Contribute a few dollars each month. See fewer ads. The money you contribute helps fund the sites you visit.

Google-Contributor supports websites while reducing advertisements. You can support InspectApedia with a contribution of any amount you wish. Or you can contribute nothing and we'll still keep our website free to all readers - supported by advertising. Either approach is OK.