Why Do Bricks Go Black?

If your brick walls have black stains, chances are the cause is soot. Soot accumulates when coal, wood or gas burn in a fireplace and deposits itself on brick surfaces as ash or debris.

Dirt can accumulate on brick surfaces as well. A quick brooming job with a cleaning product specifically made for brick can often remove built-up dirt.

Table of Contents


Brick is typically very weather-resistant, yet even its toughest layers may succumb to water damage and become discolored or crack or crumble over time. If you notice dark stains on your brick surfaces it is essential that they are identified quickly so the issue can be addressed appropriately.

Stains like this one can be caused by many different things, but in most cases are caused by excessive moisture. This could occur as the result of an unfixed leak in the building, or too much water being used on an outdoor surface such as garden beds or surfaces for gardening. If there appears to be too much moisture on or under your brick, it would be wise to contact a professional as soon as possible to inspect and address this problem.

Black stains on brick are typically caused by soot or creosote that has collected in a fireplace, and can easily be remedied by regularly using a bristle brush and mild cleaning solutions such as vinegar or tri-sodium phosphate to scrub it away with regularity.

An efflorescence stain on brick is another type of stain, which appears as a white deposit known as efflorescence. This chalky accumulation forms when moisture evaporates, leaving behind mineral salts on its surface – this phenomenon is entirely normal and affects both new and older brick surfaces alike.

Sometimes a water leak can also result in the appearance of stair-step cracks in a brick wall, particularly if bricks are laid vertically instead of horizontally. This phenomenon may be the result of ground movement, frost or inappropriate foundations – all factors to be taken into account if you detect such an anomaly on your walls. As soon as it appears it should be repaired by a qualified mason to avoid structural damage to your home and avoid potential costly stains on its surface that were discussed here in this blog article.


Brick has long been used in homes, schools, office buildings and other structures due to its durability. If you own or are maintaining a home made from brick, patios or walkways it is vitally important that it is regularly cleaned to remove dirt, pollutants and any staining on its surface. There can be various causes for black stains on brick so it is crucial that you identify what type of staining exists so as to quickly and completely address it.

Dirt is often responsible for staining brick surfaces with dark stains. This is especially prevalent on exterior brick walls that may be subject to debris from their environment, including rain. A thorough cleaning with either brooms or power washers should remove most dirt. To be on the safe side when selecting brick cleaner products for cleaning purposes, always test on an inconspicuous area first to make sure it does not cause further damage to the brick.

Carbon stains are another cause of brick discolouration. If your brick is located near a busy road, parking lot, or construction site it may become stained from emissions from vehicle exhaust and other fumes that discolour it further. In such instances, an acid formula cleaning solution can be used to break down carbon deposits; always follow manufacturer recommendations when using such cleaners on brick to avoid permanent damage to it.

Brick walls may also become stained from mold or algae growth, making these types of stains more challenging to treat than regular dirt stains. Professional services should always be sought as treatment may involve chemical strippers which require special handling, wrapping and disposal in order to minimize environmental issues.

Black stains on brick can typically be cleaned using simple cleaning methods. A good way to determine whether or not the stain comes from dirt is to gently rub the stain with a damp sponge; if this causes it to come off, they likely stem from mold or algae and can be treated accordingly; otherwise further investigation must be conducted into what caused these black marks on your brick wall.

Lichen or Moss

Mosses and lichens thrive in damp, dark places and can quickly take over patios and brick walls. Not only are they unsightly, but their slippery surfaces may lead to children or seniors falling and cause injury. Furthermore, these blooms could indicate dead or damaged branches as an indicator for tree problems.

Moss infestations are typically straightforward to clear away with just a brush and hose; however, in cases where they have been present for an extended period, using a pressure washer and chemical stripper may be necessary.

Lichens differ significantly from mosses in that they’re comprised of more complex organisms. While mosses form simple green mats, lichens have complex organisms with symbiotic relationships between fungi and algae or cyanobacteria (blue-green bacteria). Lichens don’t have roots so must absorb water and nutrients from the air – unlike plants which produce flowers or seeds for reproduction via pollen and seeds; reproduction happens through spores instead.

Algae thrives in moist environments, making it a likely culprit behind unsightly black stains on brick walls. Not only are the discolorations unsightly but their slippery nature poses an increased risk of falling for both children and seniors.

Stains may be relatively straightforward to remove, but their presence can cause permanent damage by blocking brick pores and impairing their ability to breathe, which over time loosens mortar joints and wears away at brickwork.

If you notice white streaks appearing on the top face of a brick wall, they could be due to lime run and not efflorescence. Water flows through holes and cracks in the brick, dissolving calcium carbonate into solution before depositing it on its surface.

Professional cleaning products like Wet & Forget Outdoor can be invaluable in protecting brickwork from black stains, lichen and moss growth on its surface. As non-toxic and eco-friendly solutions go, this one should ensure clean masonry for up to 12 months after application – make sure it dries fully within 4-5 hours so rainwater doesn’t reactivate it before rain arrives again.


Algae are multicellular plants that range from single cells to huge colonies (depending on the species). Algae capture carbon dioxide and provide oxygen, and form symbiotic relationships with nonphotosynthetic organisms like lichen or mosses (nonphotosynthetic organisms that do not convert light directly to energy). They have been found across habitats – from Antarctica’s frigid waters, mountain top lakes and tropical rain forests all the way to tree trunks, animal fur, snow banks and hot springs (Current Biology 2014).

If black stains appear on your brick walls, it is essential that you identify their source so you can take effective action to eliminate them. Be it from lichen, moss or algae growth, the stains must be eliminated by employing appropriate cleaning methods in order to stop their return.

Soot or creosote-related stains could indicate that there has been a chimney fire nearby; such stains should be cleaned up immediately as they can present a fire risk. Black spots on walls could also be due to vehicle emissions if your building is near busy road junctions or construction works.

Efflorescence is a common problem in brick buildings and is to be expected when exposed to weather elements. It occurs when salt dissolves in the brick, drawing water onto it and pushing it to the surface, leaving unsightly deposits behind on walls exposed to these conditions. To clean, start by scrubbing with a brush to loosen dirt, using pressure washer on its lowest setting to avoid brick damage, then using brick cleaner that dissolves salt deposits while thoroughly rinsing after each use.

To prevent efflorescence from reappearing, it’s advisable to apply a brick sealant. This will stop water penetrating porous house bricks and drawing salt ions to the surface, allowing them to dry quickly without returning and prompting efflorescence to return. For optimal results, apply this sealant during periods of warm weather to ensure adequate drying out time of your bricks.