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

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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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

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

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

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

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


Continue reading at STAIN DIAGNOSIS on BUILDING EXTERIORS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see CONCRETE STAIN CAUSE & CURE FAQs - questions and answers posted originally on this page.


Or see STAINS on STONE, STUCCO DIAGNOSE & CURE for cleaning methods


Suggested citation for this web page

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


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