QuickTake summary
- Houston’s year-round humidity (averaging around 75%) drives algae, mildew, and efflorescence onto brick faster than in drier climates, so most homes need exterior brick cleaning every two to three years.
- The safest approach starts with a garden hose, a natural-bristle brush, and mild detergent; pressure washers should stay at or below 800 PSI with a wide-angle tip to protect mortar joints.
- Muriatic acid (hydrochloric acid) removes stubborn mineral stains, but the CDC classifies it as a corrosive substance that can cause irreversible eye damage and skin burns without proper PPE [1].
- Always patch cracked or crumbling mortar and let repairs cure for at least seven days before any wet cleaning, or water will push behind the brick and breed mold inside the wall cavity.
- If your brick shows widespread mortar erosion or you are dealing with stains you cannot identify, a professional exterior cleaning crew has lower-risk methods and the right equipment. Advantage Pro Services offers house washing across Houston for exactly this situation.
Houston homeowner snapshot
Houston sits in a humid subtropical climate zone where morning relative humidity regularly tops 90% during summer, and afternoon readings rarely drop below 60% [2]. That moisture, combined with Gulf Coast warmth and frequent afternoon thunderstorms, creates a near-perfect environment for biological growth on porous surfaces. Brick and mortar are both porous. They absorb rainwater, hold it, and release it slowly. In Houston’s climate, the release cycle often cannot keep pace with the intake, which means mold, algae, and mineral deposits gain a foothold much faster here than they would on a brick home in, say, Denver or Phoenix. Knowing this changes how aggressively you should clean, what products you choose, and how often the job needs repeating.
What you are dealing with
Brick exterior walls collect four main types of buildup in Houston: biological growth (green algae, black mold, mildew), efflorescence (white, chalky salt deposits that leach through the brick as moisture evaporates), atmospheric dirt and pollution residue, and rust or mineral staining from irrigation water. Each requires a different cleaning approach, and using the wrong one causes damage that is expensive to fix.
The mortar between your bricks is the weak link. Mortar is softer than the brick it holds together, and it is designed to be sacrificial. Over decades, mortar erodes so that the brick itself does not. This is by design, but it means mortar is also the first casualty of aggressive cleaning. The National Park Service notes that inappropriate cleaning methods are a major cause of damage to masonry buildings and recommends always using the gentlest effective method [3]. That guidance applies to a 200-year-old courthouse and your 2004 ranch home in Katy equally.
High-pressure water, wire brushes, and full-strength acid are the three most common ways homeowners accidentally destroy mortar. Pressure above 800 PSI can blast mortar out of joints in a single pass. Wire brushes scratch brick faces, opening pores that trap more dirt than before. And undiluted muriatic acid dissolves the calcium compounds in mortar, weakening bonds that took years to cure.
The EPA recommends keeping indoor relative humidity below 60% to discourage mold growth [4]. Exterior brick in Houston lives well above that threshold for most of the year, which is why the stuff grows back predictably and why cleaning is a recurring task, not a one-time fix.
Do it right, do it safe
Step 1: Inspect before you touch anything. Walk the perimeter and look at the mortar joints. Press a screwdriver tip into the mortar in several spots. If it crumbles easily or you can gouge out chunks, you need repointing before cleaning. The NPS advises patching damaged joints and allowing at least seven days of cure time before introducing any water [5]. Cleaning over failing mortar drives water deep into the wall assembly, which in Houston’s climate will almost certainly produce hidden mold.
Step 2: Protect everything around the brick. Cover plants, outdoor outlets, light fixtures, and any wood or metal trim with plastic sheeting. If you plan to use any chemical beyond dish soap, this step is not optional. The University of North Carolina’s environmental health office recommends blocking nearby storm drains before pressure washing to prevent chemical runoff from entering the stormwater system [6]. Houston’s MS4 stormwater regulations follow similar EPA guidance [7].
Step 3: Pre-soak the wall. Use a garden hose to saturate the brick from top to bottom. Dry brick absorbs cleaning chemicals too deeply, which can cause discoloration or leave residue you cannot rinse out. Wet brick limits how far any solution penetrates. This single step prevents most chemical staining problems.
Step 4: Choose your cleaning method based on the stain.
For general dirt and light biological growth, a bucket of warm water with a few tablespoons of dish soap and a stiff natural-bristle brush (not wire) will handle most of it. Work in three-by-three-foot sections, scrubbing in circular motions, and rinse each section before moving to the next.
For heavier algae or mildew, a solution of one cup household bleach per gallon of water is effective. The CDC confirms that bleach or detergent can remove mold from hard surfaces [8]. Apply from the bottom up (to avoid streaking), let it sit five to ten minutes, scrub, and rinse thoroughly from the top down.
For efflorescence (those white salt deposits), a stiff dry brush often removes it on its own because the crystals are sitting on the surface. If dry brushing does not work, a diluted white vinegar solution (one part vinegar to five parts water) breaks down the remaining salts without attacking the mortar.
For rust stains or heavy mineral deposits, you may need a diluted muriatic acid solution (typically one part acid to ten or twelve parts water). This is where the risk goes up sharply. The Agency for Toxic Substances and Disease Registry (ATSDR) notes that OSHA sets a permissible exposure ceiling of 5 ppm for hydrochloric acid fumes [1]. In plain terms: you need chemical-splash goggles (not safety glasses), acid-resistant gloves that extend past the wrist, long sleeves, and closed shoes. Always add acid to water, never the reverse. Work in small sections. Rinse thoroughly. And never use muriatic acid on colored or glazed brick without testing an inconspicuous area first.
Step 5: If you use a pressure washer, keep it gentle. Stay at or below 800 PSI. Use a 25-degree or 40-degree fan tip, never a zero-degree pencil tip. Hold the nozzle at least 12 inches from the surface and keep it moving. The University of Florida’s masonry design standards explicitly warn against pressure washing brick surfaces because it can deteriorate the integrity of brick and mortar joints [9]. If you follow the low-pressure approach, you reduce that risk considerably, but understand you are still applying more force than a garden hose.
Step 6: Let the wall dry completely. In Houston, this can take several days depending on the season. Do not apply any sealant until the brick has dried thoroughly. Sealing over trapped moisture is one of the most common and most damaging mistakes a homeowner can make. The NPS guidance on water-repellent coatings stresses that breathable products (silane or siloxane-based) are preferable to film-forming sealers that trap moisture inside the masonry [3].
Advantage Pro Services uses low-pressure house washing techniques specifically calibrated for Houston’s brick homes, which eliminates much of the guesswork in Steps 4 and 5.
Cost, time, and outcome expectations
A DIY brick cleaning job on a typical two-story Houston home (roughly 1,500 to 2,000 square feet of brick) usually takes a full weekend day if you are working by hand with brushes and a hose. Add a pressure washer and you can cut that to four or five hours, though setup and protection time stays about the same.
Materials for a DIY job run relatively low: a bristle brush, a garden sprayer, dish soap or bleach, and plastic sheeting for plant protection will cost under $50. If you need muriatic acid and the associated PPE (goggles, gloves, respirator), budget another $40 to $60.
Professional house washing for a Houston home typically falls in the range of a few hundred dollars for a single-story home up to the mid-hundreds for larger or two-story properties. That price usually includes plant protection, chemical application, low-pressure rinsing, and cleanup. The main reason homeowners hire professionals is access. Cleaning a two-story brick wall safely from a ladder while managing a pressure wand and chemical sprayer is genuinely dangerous, and falls from ladders remain one of the most common home injury scenarios.
The outcome difference between a careful DIY job and a professional job is usually minimal on single-story, easy-access walls. It grows significant on multi-story homes, homes with delicate older mortar, or situations involving unknown stains.
Common mistakes on Houston homes
Using too much pressure. This is the number one error. Homeowners rent a 3,000+ PSI machine and go to work at full blast. The mortar erodes. Water gets behind the brick. Mold develops inside the wall cavity within weeks in Houston’s humidity.
Skipping the pre-soak. Dry brick absorbs chemicals unevenly, leaving blotchy discoloration that can be permanent on lighter-colored brick.
Cleaning in direct afternoon sun. Houston summer sun dries cleaning solutions onto the brick before you can rinse them off. The NPS recommends cleaning masonry when temperatures are moderate and the surface is not in direct sunlight [3]. Early morning or overcast days are your best window.
Applying sealant to dirty or damp brick. Sealant locks in whatever is on or in the brick at the time of application. If that includes moisture, dirt, or chemical residue, you are sealing in future problems. The EPA notes that moisture trapped behind barriers promotes mold growth [4].
Using wire brushes on the brick face. Wire bristles scratch the fired surface of the brick, exposing the softer interior to faster weathering. Natural-bristle or nylon-bristle brushes are the correct choice for scrubbing. The NPS specifically recommends stiff natural bristle or nylon brushes for cleaning recently repointed masonry [5].
Ignoring storm drain runoff. Bleach and acid solutions should not enter the stormwater system. The EPA’s NPDES stormwater program regulates discharges from construction and industrial activities, and commercial pressure washing operations can fall under these rules [7]. Even for DIY work, directing chemical-laden runoff away from storm drains is the responsible practice.
Pro-level solutions
Professional brick cleaning crews in Houston generally use a method called soft washing. This involves applying a surfactant-based cleaning solution at very low pressure (often just gravity-fed or at around 60 to 100 PSI), allowing it to dwell for several minutes while it breaks down biological growth and loosens dirt, and then rinsing at low pressure. The chemical does the work, not the water force.
For stubborn stains, professionals have access to commercial-grade brick cleaners formulated to target specific stain types (iron, manganese, vanadium, carbon) without the collateral damage of generic muriatic acid. These products are pH-balanced for masonry and carry far less risk to mortar joints than hardware-store acid.
Professionals also use downstream injection systems that introduce cleaning solution into the water stream after the pump, keeping the solution away from pump internals and allowing precise dilution control. This level of precision matters on Houston brick because the combination of heat, humidity, and varied brick composition across neighborhoods (older Montrose bungalows use very different brick than newer Sugar Land construction) means no single dilution ratio works everywhere.
Advantage Pro Services has been cleaning Houston homes since 1999 and adjusts technique based on the age and condition of the brick and mortar, which is the kind of judgment call that comes from doing this work across thousands of local properties.
Key takeaways
- Start with the gentlest method (brush and soapy water) and escalate only if the stain does not respond. Every step up in chemical strength or water pressure adds risk to your mortar.
- Repair any cracked or crumbling mortar joints before cleaning, and wait a full week for the new mortar to cure. Cleaning over damaged joints pushes water into the wall.
- Houston’s humidity means biological growth on brick is a recurring maintenance task, not a problem you solve once. Plan to inspect and spot-clean annually, with a full wash every two to three years.
- If your brick is pre-1960s, shows significant mortar erosion, or has stains you cannot identify, bring in a professional. The cost of a pro wash is a fraction of the cost of mortar repair after aggressive DIY cleaning goes wrong.
- Always wear proper PPE when using any chemical stronger than dish soap, and keep runoff out of storm drains.
FAQ
What PSI is safe for cleaning brick in Houston?
Stay at or below 800 PSI with a wide-angle fan tip (25 or 40 degrees). The University of Florida’s masonry standards warn against pressure washing brick because it can compromise mortar integrity [9]. Low pressure with a good cleaning solution gets the job done without the risk.
Can I use bleach on exterior brick?
Yes. A solution of one cup household bleach per gallon of water effectively kills mold and algae on brick. The CDC confirms bleach removes mold from hard surfaces [8]. Pre-soak the brick, apply from the bottom up, let it dwell five to ten minutes, scrub, and rinse from the top down. Protect nearby plants with plastic sheeting.
What causes white chalky stains on Houston brick walls?
That is efflorescence, the result of water-soluble salts inside the brick or mortar migrating to the surface as moisture evaporates. Houston’s cycle of heavy rain followed by heat and sun accelerates this process. Most efflorescence brushes off dry. Persistent deposits respond to a diluted vinegar rinse.
How often should I clean my brick exterior in Houston?
Most Houston brick homes benefit from a full cleaning every two to three years, with annual spot-treatment for any visible algae or mildew. Walls on the north side of the house or shaded by trees will need attention more frequently because they dry more slowly, which the EPA notes creates conditions favorable to mold growth [4].
Is muriatic acid safe to use on brick?
It can be, but the margin for error is small. Muriatic acid (hydrochloric acid) is classified as a corrosive hazard under OSHA’s Hazard Communication Standard, and the ATSDR notes that even brief skin contact can cause severe burns [1]. Always dilute to at least one part acid to ten parts water, add acid to water (never the reverse), wear chemical-splash goggles and acid-resistant gloves, and test on an inconspicuous area first. On older or soft brick, avoid it entirely.
When should I hire a professional instead of cleaning brick myself?
Hire a pro if your home is two stories or taller (ladder work with chemical sprayers is hazardous), if the mortar is visibly eroding in multiple areas, if you have stains you cannot identify, or if the brick is older than 50 years. Older brick tends to be softer and more vulnerable to both chemical and pressure damage. A professional crew will assess the brick and mortar condition before choosing a method, which prevents the kind of damage that turns a $300 cleaning job into a $3,000 repointing project.
References
[1] Agency for Toxic Substances and Disease Registry (ATSDR). “Medical Management Guidelines for Hydrogen Chloride.” https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=758&toxid=147
[2] National Weather Service, Houston/Galveston. “Houston IAH Extremes, Normals, and Annual Summaries.” https://www.weather.gov/hgx/climate_iah_normals_summary
[3] National Park Service. “Preservation Brief 1: Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings.” https://www.nps.gov/orgs/1739/upload/preservation-brief-01-cleaning-masonry.pdf
[4] U.S. Environmental Protection Agency. “A Brief Guide to Mold, Moisture, and Your Home.” https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home
[5] National Park Service. “Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings.” https://home1.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm
[6] University of North Carolina, Environment, Health and Safety. “Pollution Prevention During Pressure Washing.” https://ehs.unc.edu/topics/stormwater/pollution-prevention/pressure-washing/
[7] U.S. Environmental Protection Agency. “NPDES Stormwater Program.” https://www.epa.gov/npdes/npdes-stormwater-program
[8] Centers for Disease Control and Prevention. “Mold Clean Up Guidelines and Recommendations.” https://www.cdc.gov/mold-health/about/clean-up.html
[9] University of Florida, Planning, Design and Construction. “Masonry Design and Construction Standards.” https://pdc.ufl.edu/wp-content/uploads/2025/03/dcs-6-040000.pdf
[10] National Park Service. “Preservation Brief 6: Dangers of Abrasive Cleaning to Historic Buildings.” https://www.nps.gov/tps/how-to-preserve/briefs/6-dangers-abrasive-cleaning.htm
