Algae on a brick wall © InspectApedia readerStains on Brick Surfaces
How to identify, clean, or prevent stains on brick surfaces, chimneys, walls, floors

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

Stains & discoloration on brick surfaces:

This article describes the causes & cures for various types of stains found on brick surfaces both outdoors and indoors. We list the common sources of stains on brick chimneys, walls, walks, and ceilings.

The article distinguishes among common brick stain sources such as algae, bacteria, lichens, moss, soot, sulphur, fungal growth, and other causes of markings on brick.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Stains on Brick Surfaces

Stains on brick dungeon, Goodrich Castle, Ross on Wye, Herefordshire England (C) Daniel Friedman

Article Contents

[Click to enlarge any image]

Photo above, brick (and stone) staining in the dungeon at Goodrich Castle, Ross on Wye, Herefordshire, England, UK.

Brick Chimney Stains

Below our photograph at left shows white gunk on the exterior surface of a chimney. This is almost certainly efflorescence, a mineral salt left behind as water leaks into and evaporates out of the brick chimney. The right-hand photo shows black soot staining at the top and sides of a brick chimney. If this soot is from an oil fired heating appliance, a service call is needed.

Effloresence white stains on a chimney (C) Daniel Friedman Dark stains on masonry chimney trarced to algae (C) Daniel Friedman

[Click to enlarge any image]

See EFFLORESCENCE SALTS & WHITE DEPOSITS for steps to cure efflorescence and to remove it from brick or other masonry surfaces.

Below we see black or brown tarry stains on the surface of a chimney visible in an attic. These are most likely creosote, or creosote mixed with soot that has leaked through openings in this antique brick chimney and its flue. We discuss this chimney and what to do about it

Stains indicate chimney leaks and damage (C) Daniel Friedman

See CHIMNEY STAINS & LEAKS for a catalog of stains appearing on, in or around all types of chimneys.

Watch out: water damage or soot, creosote, or other blockages of chimneys may make the chimney or flue unsafe.

Stains on Brick Exterior Walls

Black, dark, or green stains on exterior brick

Algae on a brick wall © InspectApedia reader

A reader asked us for an opinion of the cause of the green and black stains on this exterior brick building wall. While a closer on-site inspection or in some cases a forensic lab analysis of a tape lift of the brick wall surface would be needed for certain identification, this looks much like black and green algae growing on the wall surface.

The reader noted that the dark staining on this brick was occurring only below an area where roof drainage was spilling down the building wall, and s/he asked for advice about how to clean this surface, and whether power-washing would be ok.

To minimize the chances of damage, we like to start cleaning with the most gentle approach first to see if that's sufficient.

Power washing may be OK on this modern hard-fired clay brick wall as long as the washer does not spray water into the wall cavity through weep holes or other openings.

More black stains on an exterior brick wall are shown just below. These are due to rain-splash-up from the lower roof onto the brick sidewall. The increased moisture level has encouraged algal growth on the brick surface.

Black stains on a structural brick wall (C) Daniel Friedman 1st Presbyterian Church, New York

Green Stains on Exterior Brick Walls: Algae

Green algae growth on brick wall (C) Daniel Friedman Green algae growth on brick wall (C) Daniel Friedman

Above the green stains on this structural brick wall (Vassar College, Poughkeepsie, New York, USA) are almost certainly an algae growth. The wall is shaded and roof drainage system leaks have made this wall side particularly wet. Later, after the roof drainage system had been repaired, this wall was renovated and portions of it that had been frost-damaged were re-built.

White Stains on Brick Walls: Efflorescence vs. Paint Pigment Run-down vs. Mortar SNAFUs

White effloresence stains on an exterior brick wall, Vassar College, Poughkeepsie NY (C) Daniel Friedman White paint pigment run-down stains on a brick wall (C) Daniel Friedman

Earlier we illustrated white efflorescence staining on a brick chimney, a common spot where efflorescence appears outdoors on masonry buildings. Our photo at above left, showing thick white deposits on a structural brick wall in New York (Vassar College) shows that efflorescence can show up anywhere that there are water leaks in or down brick walls.

But not all white stains on brick surfaces are due to efflorescence At above right the white stains on this brick veneer wall were caused by leaks into the white coated aluminum soffit. White pigment from the soffit has run down the wall leaving a white deposit. There was a bit of green algae in the top area of this stain too.

Really? Brick veneer? Yes. Before you write to gripe that the small brick-ends indicate a bond course making this a structural brick wall let me explain that no, this is a brick veneer wall constructed by a retired mason who took delight in making it look like a structural wall. The wall is actually a single wythe brick veneer fastened to a concrete block structural wall.

Below we illustrate another white area on a brick wall that is not due to water or leakage nor to paint pigment wash-down. .

Tuckpointed brick wall of a pre-1900 home, Wappingers Falls New York (C) Daniel Friedman

The white "stains" on the brick exterior wall shown above are not stains at all but rather mismatched mortar used by a mason or an amateur who had little concern for preserving this pre-1900 home in Dutchess County, New York. The bricks in this wall were already spalling but the use of a harder mortar for the repair work is likely to accelerate the spalling damage to this home located in a freezing climate.

Brick wall stain removal by cleaning, power washing, sand-blasting: warnings

Watch out: Experts like Grimm (1990) widely warn against sand-blasting to clean brick surfaces of buildings. That aggressive approach damages the brick and mortar and can lead to rapid deterioration of the wall.

Furthermore, on antique, soft brick, even power washing can remove the brick's harder-fired surface, leaving the softer brick interior vulnerable to water and frost damage and causing costly building damage. Power washing can also remove older soft mortars. And even on the modern hard clay brick wall, the washer needs to be used with care, starting from a more distant position in order to avoid leaving too-light power-sprayer marks on the wall.

Extra care must be taken if cleaning a brick-veneer wall as there may be more weep openings or leaks around window or door penetrations through which water may be inadvertently sprayed into the wall cavity.

Other brick wall cleaning methods such as using lasers, photocatalytics, or special cleaners are discussed both at
the REFERENCES for this article

Stains on Exterior Brick Floors, Patios, Walks

At below left the black stains on this exterior brick patio located in New York state are probably algae but might also be a fungus. We'd need to examine a sample in the lab. At below right we see moss growth on the same brick patio in a nearby area. This is a shaded brick patio constructed in the late 1990's. As plantings grew and a shade tree's canopy began to keep more of the patio area in shade in summer months the area covered by algae, moss, and possibly fungi has grown.

Algae & possibly fungi on Brick patio surface (C) Daniel Friedman Moss on Brick patio surface (C) Daniel Friedman

Remedies to reduce the staining on the brick shown above include assuring proper drainage, increasing the sun exposure by judicious pruning, sweeping off organic debris that hold water on the surfaces (leaves), and occasional power-washing.

Watch out: algae and moss on a brick walking surface or on any walking surface for that matter, are very slippery and risk a slip-trip-fall injury.
See SLIPPERY STAIRS, WALKS for the static coefficient of friction of various slippery walking surfaces.

Below we illustrate outdoor brick patio or walk surfaces that are not slippery with algae, moss, fungi. At below left is the same brick patio whose bricks were shown above - but at below left, photographed about ten years earlier, the brick patio was new, sunny and free of slippery algae or moss.

Brick patio not slippery (C) Daniel Friedman Antique bricks used in a walkway, New York (C) Daniel Friedman

Above at right we illustrate that a brick walkway, even one built using antique bricks that have been in place for more than 50 years do not have to be slippery with algae, moss, nor fungi. The Dutchess County New York brick walkway shown above is in a sunny area and is well drained. However the property manager does need to keep alert for frost-heaved or broken bricks that might form a trip hazard.

Stains on Interior Brick Wall, Ceiling, or Floor Surfaces

Stains on brick dungeon, Goodrich Castle, Ross on Wye, Herefordshire England (C) Daniel Friedman Creosote & soot stains on stone fireplace, Elk Lake Michigan USA (C) Daniel Friedman

Above at left, notice the dark stains on the rear wall and white efflorescence stains on the ceiling of the dungeon at Goodrich Castle, Ross on Wye, Herefordshire, England, UK. Both of these stain sets can be ascribed to water entry, but we also observed moss and even some fungi growing on these walls.

At above right are very black creosote and soot stains on the hearth-face of a stone fireplace installed in a hand-built log cabin at Elk Lake Michigan.


Finding and fixing leaks into or onto brick structures is a key step in stopping the formation of algae, moss, efflorescence, or fungal staining on brick surfaces.

How to Remove Paint from Brick or Stone Surfaces

Painted brick wall collapsing Sheffiled Stable NY (C) Daniel Friedman

Here is a summary of good practices when you need to remove any type of paint from an exterior or interior brick wall, fireplace, or other surface. These methods also work well for stone surfaces.

[Click to enlarge any image]

Question: How do I clean off paint run-down from white siding on brick

White stains on brick from aluminum or vinyl siding or trim (C) Daniel Friedman

1 June 2016 dennis said:
how do i clean paint pigment run down from white siding on brick



How to Remove Paint Chalk Rundown from Brick Surfaces

If you are asking only about the simple deposits of runoff from a chalking painted surface, I recommend gentle cleaning of the brick with a natural bristle brush and a TSP substitute cleaning solution. You can also try household detergent. Please see our warnings below about the dangers of aggressive cleaning or power washing of brick surfaces.

Don't waste time trying bleach as some of our readers did. Bleach won't remove white paint pigment and bleach itself, running down building surfaces can leave white streaks if not washed-off quickly enough.

How to Remove Actual Paint or other Coatings from Brick Surfaces

Black tarry coating on brick (C) Daniel Friedman

Before starting, for best results in brick surface cleaning you need to know

  1. The kind of paint you want to remove, as paint chemistry defines what solvents work best on it - latex is different from alkyd or old oil-based paint. I experiment with soap and water, mild cleaners such as vinegar, even dish soap or TSP substitute, and for some paints I might try lacquer thinner, odorless paint thinner, and peel-away paint stripping coatings.

    In the photo above we see thick black coating on part of a brick exterior wall of a Vassar Farm building in Poughkeepie, NY, USA. This is tar, not paint. Most paint removal treatments will just make a mess on this surface.
  2. The amount of paint to be removed, as a small scale cleaning project may take a different approach from cleaning an entire brick (or stone) surface that has been painted over. A large area project is going to require drop cloths, protective gear, and probably two stages of chemical stripping followed by gentle brush and wash cleaning of the brick surface.
  3. The nature of the brick (or stone) surface - as glazed brick or hard stone is easier to clean with solvent while soft brick or soft stone such as brownstone or sandstone are at risk of absorbing solvent-borne pigments. Soft brick and mortar also absorb more water and are at greater risk of frost damage if soaked right before freezing weather.

So I don't think there is a single "right" answer that's optimum for all conditions.

Brick Cleaning Mistakes to Avoid

Watch out: For people who are going to jump to "how to" let's first warn off some mistakes that you'll regret:

Spalling brick wall possibly damaged by sandblasting (C) Daniel Friedman

Recommended Cleaners or Strippers for Brick or Stone Surfaces

Choose a paint removal method that suits the amount of paint, type of paint, and condition of the brick or stone itself. A peel away paint remover may also work on some masonry surfaces. Try Citri-Strip for a less-toxic cleaner that may work on your paint. Newer peel-away chemical paint remover systems that use a fabric + thick paint-on chemical paste can pull paint off of the brick.

  1. Prepare the work site: Put down 6-mil poly to catch paint and drippings safely while avoiding contaminating soil below the wall.
  2. Prepare the workers: Wear protective gear appropriate for the chemicals used. Some paint stripping chemicals are carcinogenic, some can cause dangerous burns or eye damage, some produce harmful VOCs and may require use of a respirator. Old paints contain lead that can poison workers who don't protect against dust or fumes.
  3. Apply the strip or cleaning solution. If you are using a peel away method, basically you put down dropcloth, coat the surface, apply fabric strips, wait, peel away the fabric that carries away most of the paint.
  4. Final cleanup: Wash / clean the brick surface after the main body of paint has been removed. Even after using the paint stripper you will probably have to do some additional gentle scrubbing on the brick surface as some pigment may remain.
  5. Dispose of waste: Read the disposal recommendations from the manufacturer of the chemical or paint stripper you are using before starting the job. Lead paint chips or debris may also require special handling, wrapping, disposal.

Take a look at some of the brick cleaning references I will cite below, especially work where Grimmer was involved.

Resources for Removing Paint from Brick or Stone Surfaces

Paint coating on brick foundation wall (C) Daniel Friedman

Research on brick surface troubleshooting, cleaning, repair

Stone & Masonry Stains & Cleaning Articles


Continue reading at STONE SURFACE CLEANING METHODS for cleaning approaches useful for brick or stone surfaces, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see MOLD APPEARANCE - STUFF THAT IS NOT MOLD for other discolouration found on brick surfaces.


Suggested citation for this web page

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


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


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

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman