To clean brick safely, match your method to your brick type and stain type. Hard modern machine-pressed brick tolerates diluted acidic cleaners, low-pressure washing, and oxygen bleach. Soft pre-1920 common brick and Indiana limestone facing cannot tolerate high pressure, muriatic acid, or film-forming sealers without permanent surface damage. On most homes, gentle scrubbing with appropriate diluted solutions and a thorough rinse is all you need.
For common stains on sound brick in good repair, the process is straightforward. For walls with deteriorated mortar joints, efflorescence, or soft historic materials, the cleaning conversation starts with fixing the underlying condition, not the stain on top.
Since 1987, Delta - Masonry and Tuckpointing has assessed brick cleaning questions across Chicago’s North Shore and northwest suburbs. Here is what separates a safe result from an expensive mistake.
What Brick Type Do You Have?
The single most important question before cleaning brick is whether the material is hard or soft. Getting this wrong destroys the surface.
Hard machine-pressed brick was manufactured from the 1920s onward using high-pressure kilns that produced a dense, uniform, durable face. Post-war homes throughout Northbrook and Glenview are built with this material. It tolerates gentle pressure washing, diluted acid cleaners, and most commercial masonry products within their labeled guidelines. Northbrook’s median home age is approximately 1968, and these builder-grade brick facades have accumulated decades of surface soiling that responds well to controlled washing.
Soft common brick from the pre-1920 era was hand-molded and kiln-fired at lower temperatures. It is more porous, less dense, and the surface texture is irregular. Chicago bungalows, Evanston Victorians, and Wilmette Cape Cods built before 1950 often have this material. It is easily damaged by high-pressure water, acid at even moderate dilutions, and wire brushes. Cleaning that is routine on hard brick will erode the face of soft brick within a single session.
Evanston presents both types on the same street. Pre-1920 common brick homes sit next to mid-century construction with harder materials. Before assuming your brick can handle a standard cleaning approach, know which era it comes from.
Evanston greystones add a third category: Indiana limestone facing over common brick backing. This is one of Evanston’s most common masonry configurations, particularly in the greystone two-flats and three-flats near Davis Street. Indiana limestone is a sedimentary rock composed primarily of calcium carbonate. Muriatic acid reacts directly with calcium carbonate, permanently etching the stone surface. If you have limestone facing, acid cleaning is not a matter of careful application. It is a guaranteed damage event. Use non-acidic cleaners only, apply by soft brush, and rinse thoroughly.
Understanding Efflorescence: Clean or Fix?
Efflorescence signals an active moisture problem. The white, powdery or crystalline deposit that appears on brick surfaces forms when soluble salts migrate through the material and deposit at the surface as water evaporates. The salts do not originate at the surface. They are carried from inside the masonry by water moving through failing mortar joints, cracks, or inadequate waterproofing. The white deposit is the calling card of that water movement, left behind when the water evaporates.
In Wilmette, efflorescence on basement and foundation walls is the most common masonry cleaning question we field. Wilmette’s high water table and lake-proximity humidity push moisture through foundation masonry at a rate that inland communities do not experience. Cleaning the white deposits off the surface is cosmetic. Until the moisture source is addressed through joint repair, drainage correction, or appropriate waterproofing, the deposits return within one season.
For new, dry efflorescence that has not bonded to the surface, a stiff natural-bristle dry brush removes most of it. For deposits that have bonded after repeated cycles, a diluted white vinegar solution (roughly 1 part vinegar to 12 parts water) applied with a soft brush, scrubbed lightly, and rinsed thoroughly works on hard brick. On soft historic brick, plain water scrubbing first, then diluted vinegar only if needed, and always a full rinse.
Do not use dry grinding tools or wire brushes on efflorescence deposits on soft brick. Mechanical abrasion that damages the brick surface makes the problem worse by creating more surface area for water absorption.
For walls where efflorescence is widespread and recurring, the correct sequence is: assess and repair mortar joints with removal to a minimum 3/4 inch depth per BIA Technical Note 7B, address drainage issues, then clean. Power washing brick does not address this sequence. It adds water to a wall that already has too much water.
How to Clean Brick: Safe Methods for Dirt and General Buildup
General surface dirt from environmental exposure, bird debris, and urban particulate responds to the simplest approach: water and a medium-bristle scrub brush. Pre-soak the wall with a garden hose, scrub in sections, and rinse thoroughly from top to bottom. This handles most surface grime on walls in reasonable condition.
For more stubborn general soiling, a diluted solution of dish soap or a purpose-made masonry cleaner applied with a soft brush and rinsed completely is the next step. Test any chemical product on a small, inconspicuous section and wait 24 hours before proceeding to the full wall.
The key variable is always the mortar joint condition. Applying any water to a wall with deteriorated joints forces moisture behind the brick face, where it promotes efflorescence, freeze-thaw damage in winter, and interior water infiltration. Before a wet cleaning project, do the scratch test on the mortar joints. If mortar crumbles with light key pressure or feels sandy, schedule joint repair before cleaning.
Should you seal your brick after cleaning? The answer depends on the brick type and the product. Penetrating silane or siloxane sealers reduce surface water absorption on hard brick without trapping moisture inside. NPS Preservation Brief 1 documents the risks of water-repellent treatments on historic masonry: film-forming coatings and silicone sealers on soft historic brick block the wall’s ability to breathe, trap moisture, and the freeze-thaw cycle then pops the brick face off from inside. If you have pre-1920 soft brick, do not apply any sealer without confirmed guidance for that specific material.
Organic Growth: Algae, Lichen, and Mold
Green staining on north-facing brick is typically algae growth fed by persistent moisture and low light. Black staining along the grout lines or in sheltered areas is often mold or biological growth combined with environmental carbon. Both are common in areas with tree canopy, limited sun exposure, and high humidity.
Organic growth on hard modern brick responds to diluted chlorine bleach (1 part bleach to 10 parts water) applied with a soft brush and allowed to dwell 10 to 15 minutes before thorough rinsing. Residual bleach in the joint can affect mortar over repeated applications.
On soft historic brick, use diluted oxygen bleach (sodium percarbonate, often sold as OxiClean) instead of chlorine bleach. It is less aggressive and still effective against biological staining. Dissolve according to package directions, apply by soft brush, allow 10 to 15 minutes dwell time, and rinse with a low-pressure hose.
For lichen specifically, which bonds to the stone or brick surface more tenaciously than algae, professional masonry cleaning products containing quaternary ammonium compounds are more effective than bleach solutions. These are sold at masonry supply houses and are applied per the manufacturer’s protocol.
Organic growth returns if the shade and moisture conditions that enable it remain unchanged. North-facing walls in Wilmette and Evanston with heavy tree canopy overhead will re-grow algae within a few seasons. Cleaning is maintenance, not a permanent solution, unless the underlying conditions change.
What Not to Use on Soft Historic Brick
The three most damaging cleaning methods on pre-1920 soft brick and limestone are worth stating directly.
Muriatic acid at any practical concentration damages soft common brick and etches Indiana limestone. The acid attacks the calcium content in both materials. On soft brick it increases surface porosity and can cause spalling. On limestone it leaves permanent visible scarring. NPS Preservation Brief 6 documents the irreversible damage caused by aggressive cleaning methods including acid treatment on historic masonry. The masonry cleaning industry has largely moved away from muriatic acid in favor of safer formulations that achieve the same cleaning goals without the damage risk.
High-pressure washing at settings above 300 to 500 PSI on soft brick erodes mortar joints, drives water deep into the wall, and can abrade the brick face on the most deteriorated material. The damage from a high-pressure washing session on a pre-1920 wall is often not visible immediately. It appears over the following winter as frost-damaged mortar and brick spalling from moisture that was forced in during the cleaning.
Evanston’s soft pre-1920 common brick presents exactly this risk. Many Evanston homes have been repeatedly cleaned with pressure washers as part of routine exterior maintenance. The cumulative effect on the mortar joints accelerates deterioration that would otherwise develop over decades. We have repointed Evanston walls where the mortar had been pressure-eroded to two to three times the normal depth of weathering for the building’s age.
Wire brushes scratch brick surfaces and damage mortar. Use natural-bristle or nylon brushes for scrubbing masonry at every hardness level.
The Northbrook and Glenview Standard
The post-war machine-pressed brick homes in Northbrook and Glenview offer the most forgiving cleaning situation. Builder-grade mortar on these 1960s to 1980s homes has often deteriorated significantly, but the brick itself is hard and dense.
A pressure washer set below 1,000 PSI with a 25-degree fan tip held at least 12 inches from the surface is generally acceptable on these homes. The operative word is generally. Before pressure washing any wall, inspect the mortar joints. If joints on a Northbrook split-level are already recessed and crumbling, pressure washing accelerates that deterioration and pushes water into the wall. Power washing works on hard brick walls with sound mortar joints, not on walls that need repointing.
Glenview’s ravine-side properties carry an additional complication: persistent humidity from the ravine micro-climate promotes organic growth more aggressively than on open lots. These north and east walls often need more frequent cleaning, but the soft conditions also mean that assessment of the mortar joints is essential before any wet treatment.
Northbrook’s builder-grade mortar is often uniform in color and condition across entire facades. When cleaning these homes, the joints behave similarly across the wall, which makes the pre-cleaning mortar assessment straightforward. A simple scratch test on three or four representative joints tells you whether the wall is ready for a wet cleaning or needs repointing first.
Professional Cleaning for Complex Situations
There are situations where DIY cleaning is the wrong call.
Widespread efflorescence on a foundation wall with a high water table, as seen commonly in Wilmette, requires diagnosis of the moisture source before cleaning is productive. A masonry contractor who understands the drainage and waterproofing picture gives you a cleaning plan that actually solves the problem rather than deferring it.
Evanston greystones with Indiana limestone facing require professional cleaning assessment because of the limestone’s acid sensitivity and the mixed-material facade. Different sections of the same wall need different cleaning approaches. Getting it wrong on the limestone is permanent.
Removing paint from brick and graffiti removal from masonry require specific removal products and methods based on the stain type and the substrate. Attempting these with household cleaners risks setting the stain permanently or damaging the brick surface.
Historic or architecturally significant masonry in Evanston’s historic districts or on Wilmette’s Sheridan Road properties has an additional consideration: cleaning methods that alter the surface appearance may be subject to preservation review. NPS Preservation Brief 2 provides the federal framework for historic masonry care that governs what methods are appropriate on pre-1920 soft brick. This does not mean cleaning cannot happen. It means the method matters, and documentation may be needed.
What the Mortar Joints Tell You Before You Clean
Professional masonry cleaning always starts with a mortar assessment, not a hose. If the joints are sound, cleaning is maintenance. If the joints are failing, cleaning is a water problem waiting to happen.
The scratch test is simple: run a key along a mortar joint with moderate pressure. If the mortar crumbles, powders, or leaves a visible channel, the joint is past its useful life and needs tuckpointing before any wet cleaning. If the mortar resists cleanly with only a faint scratch mark, the joint is still functional.
On a Wilmette 1940s Cape Cod with original lime mortar, a scratch test that produces crumbling is expected at this age. That home needs repointing before any wet cleaning. On a Northbrook 1975 colonial with Type S mortar, a scratch test that produces crumbling is also possible, and the same conclusion applies.
Weep holes in brick walls are another indicator. If your wall has weep holes and they are blocked or missing, wet cleaning that drives water into the wall has no exit path, and moisture accumulates in the wall cavity. Clear weep holes before any significant wet cleaning.
Schedule a Cleaning Assessment
If you are seeing efflorescence, organic growth, or general deterioration on your brick and want to know what cleaning method is right for your specific material, Delta - Masonry and Tuckpointing has served Wilmette, Evanston, Northbrook, and Glenview since 1987. We assess both the cleaning need and the mortar condition before recommending any approach. Call (847) 713-1648 or contact us online for a free on-site assessment. We handle power washing, brick repair, and tuckpointing as a complete service so the wall is clean and sealed against water intrusion.
Cleaning efflorescence without fixing the moisture source is a cosmetic exercise. The deposits are back in one season.