Professional exterior cleaning runs on four chemical families, and one of those families is regulated by the federal government as a pesticide. A product sold to kill algae, mildew or bacteria on a wall is an antimicrobial pesticide under the Federal Insecticide, Fungicide, and Rodenticide Act, and the directions printed on that product are enforceable law rather than a manufacturer suggestion. Most of the pressure washing trade does not know that, which is why so much of the advice online publishes a dilution ratio with no document behind it.
This guide names each chemical family, says what each one does and what each one cannot do, and gives the document behind every figure with the date the document was read. Where no regulator, standards body or manufacturer publishes a number, this guide says so rather than inventing one. Pressure figures are covered separately in what PSI to use for pressure washing, because the surface manufacturer publishes the pressure and the product registrant publishes the chemistry, and the two documents are not the same document.
Which four chemical families do almost all exterior cleaning?
Four families cover almost every exterior cleaning job: a hypochlorite biocide, a surfactant, an alkaline degreaser, and an acid. Sodium hypochlorite kills the living growth that makes a wall or a roof look dirty. A surfactant lowers surface tension so the solution wets and clings instead of sheeting off. An alkaline degreaser emulsifies petroleum, which hypochlorite cannot touch. An acid, usually oxalic or phosphoric, dissolves rust, tannin and mineral deposits that are not alive and therefore do not respond to a biocide at all.
- Sodium hypochlorite. An oxidizer and biocide. Kills algae, mildew, moss and lichen. Does nothing for oil, rust or efflorescence.
- Surfactants. Wetting and clinging agents. Carry no biocidal claim of their own in most exterior mixes, and exist to hold the active ingredient on a vertical surface for its dwell time.
- Alkaline degreasers. Sodium hydroxide, potassium hydroxide and citrus terpene formulations. Emulsify hydrocarbons so a rinse can carry them away.
- Acids. Oxalic acid for rust and tannin. Phosphoric acid for efflorescence and hard water scale. Both are prohibited outright by some cladding manufacturers.
A fifth product appears on wood decks: oxygen bleach, sold as sodium percarbonate. This guide publishes no concentration figure for sodium percarbonate, because no manufacturer technical data sheet for it was read during this build, and a number written from memory is worth less than an admission that the number was not sourced.
When does a cleaning product become a federally regulated pesticide?
A cleaning product becomes a regulated pesticide the moment it claims to kill or suppress microorganisms. EPA defines the category in one sentence: "Antimicrobial pesticides are substances or mixtures of substances used to destroy or suppress the growth of harmful microorganisms such as bacteria, viruses, or fungi on inanimate objects and surfaces." That EPA page was last updated January 29, 2026 and was read 2026-09-03.
EPA further describes non-public-health antimicrobial products as products that "Are used to control growth of microorganisms of economic and aesthetic significance and are not considered to be human health related", and the examples EPA lists include algae and organisms that cause "spoilage, deterioration or fouling of materials". Exterior cleaning sits squarely in that non-public-health category, because the growth on a wall is an appearance and material problem rather than a disease problem.
Two subsections of 7 U.S.C. 136j carry the consequence. Under 7 U.S.C. 136j(a)(1)(A) it is an unlawful act to distribute or sell "any pesticide that is not registered under section 136a of this title or whose registration has been canceled or suspended". Under 7 U.S.C. 136j(a)(2)(G) it is an unlawful act "to use any registered pesticide in a manner inconsistent with its labeling". Both were read from the Cornell Legal Information Institute on 2026-09-03.
Read 136j(a)(2)(G) slowly, because the reach of that clause is narrower and sharper than the trade usually assumes. A product making no antimicrobial claim is not a pesticide and 136j does not reach it, so a plain detergent is outside this rule. A product whose bottle says it kills mildew is a pesticide, and a crew that doubles the dilution because a wall looks bad has committed a federal violation regardless of whether the wall came out clean.
What does a registered pesticide label control that a contractor does not?
A registered label controls the dilution, the sites the product may be applied to, the application rate, the required personal protective equipment, and the handling and disposal directions. None of those choices belong to the operator holding the wand. That is the practical meaning of 7 U.S.C. 136j(a)(2)(G): a contractor selects the product, and the registrant already selected the dilution.
The Chlorine Institute records the same relationship from the chemistry side. In Pamphlet 96, section 2.3.2, the Institute writes that "weight percent sodium hypochlorite must be displayed on FIFRA registered pesticide products." A registered hypochlorite product therefore arrives with its own strength printed on it, and the label ratio is calculated from that printed strength rather than from a guess about what is in the drum.
Trade guidance does not override a label, and the strongest example is the roof. The Asphalt Roofing Manufacturers Association prescribes "a 50:50 mix of laundry strength liquid chlorine bleach and water" applied with a sprayer, a dwell of "15 to 20 minutes", and a rinse "with low pressure water", in a bulletin published February 22, 2012 and read 2026-09-03. That ratio is the roofing manufacturers' stated method for shingles. Where the product in the tank is a registered antimicrobial, the registered label governs the ratio and the association bulletin does not.
How strong is contractor sodium hypochlorite compared with household bleach?
According to The Chlorine Institute, Pamphlet 96, "Sodium Hypochlorite Manual", Edition 3, April 2006, read 2026-09-04, household bleach is "A solution of sodium hypochlorite, generally containing 5.25% (by weight) sodium hypochlorite or less", and an industrial strength hypochlorite solution is one "generally containing more than 7.0% (by weight) sodium hypochlorite". The Institute adds in section 2.3.2 that "Generally sodium hypochlorite solutions are produced at strengths up to 20 percent by weight sodium hypochlorite. As strength increases, stability generally decreases."
That 7.0 weight percent line is the honest boundary between what sits under a kitchen sink and what arrives on a truck. The Chlorine Institute states it as a nomenclature convention rather than as a cleaning instruction, and Pamphlet 96 publishes no wash dilution, no dwell time and no surface guidance anywhere in the document.
Two units get confused constantly, and confusing them misstates a concentration by several percentage points. Trade percent available chlorine, per Pamphlet 96 section 2.3.1.2, is "similar to grams per liter, except that the unit of volume is 100 milliliters instead of one liter", and its value "is therefore one tenth of the grams per liter." Weight percent is trade percent divided by the specific gravity of the solution. A drum labeled 12 trade percent and a drum labeled 12 weight percent are not the same drum, and only the weight percent figure is the one FIFRA requires on a registered product.
Two provenance notes belong with those figures. The edition read is Edition 3, dated April 2006, and The Chlorine Institute currently lists Edition 6, dated February 2026, which is sold rather than published openly and was not read for this guide. The copy of Edition 3 actually read was the one held in the Pennsylvania Department of Environmental Protection wastewater operator course library, not a file served by chlorineinstitute.org.
Why does a hypochlorite mix lose strength between the drum and the wall?
Sodium hypochlorite decomposes, and three variables drive how fast. The Chlorine Institute states in Pamphlet 96 section 3.8 that "bleach decomposition accelerates as temperature increases", and that while a rule of thumb predicts "a doubling of the decomposition rate for every 10 deg C (18 deg F) rise in temperature", studies "have shown that the decomposition rate increases by a factor in the range of 3 to 4 times for every 10 deg C for solutions in the range of 5% to 16% by weight of sodium hypochlorite."
Dilution runs the other way and runs harder than the arithmetic suggests. Section 3.3 of the same pamphlet states that the second order rate law "predicts that diluting the NaOCl by a factor of 2 should decrease the rate of NaOCl decomposition by a factor of 4", but that actual data shows "a factor of 2 decrease in NaOCl concentration results in an approximate factor of 5 decrease in the rate of decomposition."
Alkalinity is the third variable. Section 3.7 states that "Solutions stored at a pH of 11.9 to 13 are the most stable in typical applications", and that "Below a pH of 10.8, the rate of decomposition begins to increase significantly reaching a maximum decomposition rate in the 5-9 pH range because of the very rapid acid catalyzed decomposition." Excess sodium hydroxide is what holds a hypochlorite product up in that stable band, which is also why a hypochlorite product must never be acidified.
Put the three together and a Georgia summer becomes a chemistry problem rather than a comfort problem. A drum riding a closed truck bed through an August afternoon is inside the temperature effect Pamphlet 96 describes, and a batch mixed at seven in the morning is not the same batch at four in the afternoon. Pamphlet 96 describes manufacture, storage and handling of bulk product rather than jobsite mixing, so treat that as the physical chemistry it is and treat the registered label as the instruction it is.
What does a surfactant do, and how long does the solution have to sit?
A surfactant lowers the surface tension of the solution so the solution wets a surface and stays on it. Without a surfactant, a hypochlorite mix sprayed on a vertical wall runs to the ground before the biocide has done anything, and the wall gets wet rather than clean. Sika Corporation states the underlying point in six words in its LaHabra technical bulletin, revised March 2024 and read 2026-09-03: "The chemicals provide the cleaning, not the water pressure."
Dwell time is where surfactants earn their place, and three manufacturer documents publish a figure. Sto Corp., in "Stucco Repair and Maintenance" guide 1.01, instructs the reader to "Apply the TSP cleaning solution to the wall surface by brush or spray and allow to soak for a period of 15-20 minutes", and warns that if bleach "is not allowed sufficient time (about 15 minutes) to sit on the surface and kill the micro-organisms, algae or mildew will re-occur." Sika's LaHabra bulletin gives the same order of magnitude: "Allow the solution to soak the wall for approximately 15 minutes, but do not allow the cleaning solution to dry on the wall."
Sika also publishes the technique rule that protects the wall while the solution works: "It is recommended to keep lower elevations wet to prevent run-off from above from causing streaking." Both Sto and Sika were read 2026-09-03, and both documents describe the manufacturers' own finishes rather than cladding in general.
Notice what those three dwell figures have in common. Every one of them belongs to a surface manufacturer describing its own finish, and none of them is a pesticide label. Where the product in the tank carries an antimicrobial claim, the registered label sets the dwell and the manufacturer bulletin describes what the finish tolerates, and a competent scope satisfies both documents rather than choosing between them.
Why does sodium hypochlorite do nothing for an oil stain?
Sodium hypochlorite is an oxidizer aimed at living tissue and pigment, and motor oil is neither. Removing petroleum takes an alkaline degreaser, which saponifies the hydrocarbon into something water can carry, or a citrus terpene formulation that dissolves it. Spraying hypochlorite on a parking deck oil drop lightens the concrete around the stain and leaves the stain.
Gwinnett County puts dry cleanup ahead of any chemistry at all. Water Quality Protection Guideline WQ-1, "Surface Cleaning", dated 04/05/2007 and read 2026-09-03, requires at section 3.1(1) that oil and fuel be taken up with absorbents, that powders and loose dirt be swept or vacuumed, and that litter and animal waste be collected, all before wash water is generated. Section 3.1(7) then limits the operator to the minimal amount of the least toxic cleaner, and directs that where possible the surface be cleaned with potable water and no chemicals at all.
The absorbent that soaks up the oil then has its own rule. Under 40 CFR 279.10(c)(1), materials contaminated with used oil "from which the used oil has been properly drained or removed to the extent possible such that no visible signs of free-flowing oil remain" are "not used oil and thus not subject to this part", while 40 CFR 279.10(c)(3) states that oil "drained or removed from materials containing or otherwise contaminated with used oil is subject to regulation as used oil under this part." Both were read 2026-09-03 from the Cornell Legal Information Institute. The drained pad and the drained oil part company at that point, and 279.10(c)(1)(ii) routes the drained material to the hazardous waste regulations where those apply.
What removes rust, tannin and efflorescence from masonry?
Rust and tannin are metal and plant stains rather than growth, so a biocide has no effect on either. Oxalic acid chelates iron and lifts rust and oak tannin out of concrete and wood. Phosphoric acid attacks the calcium salts that surface as efflorescence on brick, block and stucco, which is why Sika titles its bulletin "Procedure for Cleaning Finish & Removing Efflorescence in EIFS and Stucco".
Two hard rules attach to acids on an exterior job. An acid must never be mixed with a hypochlorite product, because acidifying hypochlorite drives it out of the stable band Pamphlet 96 describes and releases chlorine gas. An acid must also never touch a surface whose manufacturer prohibits it, and at least one common cladding does exactly that: James Hardie states in Technical Bulletin #20, "Cleaning James Hardie Primed and ColorPlus Technology Siding", November 2018, that "Acid washing can damage the fiber cement surface and is not recommended", alongside "Sand blasting can damage the fiber cement surface and is not recommended."
Solvents carry a similar prohibition on insulated finishes. Sto Corp. instructs the reader not to "Use solvent based cleaners - acetone, gasoline, ketones, mineral oils, or turpentine - for example, since solvent can penetrate the EIFS finish and base coat materials and damage the EPS insulation board." The James Hardie bulletin was read 2026-09-02 and the Sto guide 2026-09-02, and the copy of the James Hardie bulletin actually read was the one held in Home Depot's product document library, because the manufacturer hosted file did not serve on that date.
Which surfaces limit what chemistry may touch them?
Four manufacturers publish chemical limits for their own products, and each limit stops at that manufacturer's product line. James Hardie prohibits acid washing and sand blasting on fiber cement and adds that "Damage to siding arising from improper cleaning or maintenance may not be covered by the James Hardie warranty." Sto Corp. prohibits solvent based cleaners, and prohibits "steam cleaning or other high temperature cleaning methods, since the EPS insulation board in the EIFS has a service temperature limit of about 165 deg F (74 deg C)."
Sika publishes the most useful warning in this entire pack for a hot humid state, and states it in its own words: "Trisodium phosphate detergent is a food source for mold. Do not use trisodium phosphate detergent without bleach in hot humid climates. Mold must be removed with bleach, or it will return." Sika also gives a killing ratio for its own acrylic finishes: "To kill mold or mildew, apply a solution of 1 part bleach and 20 parts water to the wall or other biocide that is safe for acrylic type finishes."
Composite decking manufacturers restrict the machine rather than the chemistry. Trex permits a pressure washer "that has a fan attachment/adjustment and soap dispenser", and TimberTech states that "A power washer can be used for rinsing only with TimberTech products". Both were read 2026-09-03. Cleaning a composite deck is therefore a soap and rinse operation on both product lines, whatever a contractor is used to doing on wood.
The pattern across all four is the same and it is the whole point of this section. Every chemical prohibition on a building belongs to the company that made that specific product, so a wall has to be identified before a chemical is chosen. Related reading: cleaning stucco without damaging the finish, pressure washing compared with soft washing, and whether soft wash roof cleaning is safe.
Is there a biodegradable cleaner that may go down a storm drain?
No such product exists, and a county government says so in capital letters. Gwinnett County states at section 3.1(10) of Water Quality Protection Guideline WQ-1: "There are NO 'environmentally friendly' or 'biodegradable' cleaning products that are approved for discharge to storm drains." That guideline is dated 04/05/2007, runs 13 numbered pages, and records that the document "was developed in cooperation with the Power Washers of North America".
The federal rule behind that sentence is a definition rather than a slogan. Under 40 CFR 122.26(b)(2), an illicit discharge is "any discharge to a municipal separate storm sewer that is not composed entirely of storm water except discharges pursuant to a NPDES permit (other than the NPDES permit for discharges from the municipal separate storm sewer) and discharges resulting from fire fighting activities." Wash water carrying surfactant, hypochlorite residue and lifted organic material is not composed entirely of storm water, so wash water reaching a storm drain is an illicit discharge unless a permit says otherwise. 40 CFR 122.26 was read 2026-08-31 from the Cornell Legal Information Institute, and the EPA NPDES Stormwater Program page the same day.
The Brick Industry Association states the same rule from the trade side in Technical Notes on Brick Construction 20, "Cleaning Brickwork", August 2018 edition, read 2026-09-02: "Some jurisdictions may require containment and treatment of the runoff water before it can leave the site. Dilution of runoff and its release into the stormwater management system should not be expected or allowed unless expressly permitted by the applicable jurisdiction." Sto Corp. and Sika both close their cleaning procedures by telling the reader to check local regulatory requirements for disposal of wash water and cleaning solutions.
Where is wash water carrying these chemicals allowed to go?
Gwinnett County's guideline is the most detailed published answer in metro Atlanta, and section 3.2.1 makes the sanitary sewer or a properly permitted on-site wastewater system the default destination. Section 3.2.1.1 lists the sanitary sewer standards Gwinnett County Department of Public Utilities administers, expressly as a partial list: temperature less than 150 degrees F, pH between 5.5 and 10.5, oils and grease less than 200 mg/L, and total petroleum hydrocarbon 20 mg/L. Section 3.2.1.1(e) requires an oil or water separator where oil or grease is present, and 3.2.1.1(g) restricts discharge to private parts of the sewer rather than a public manhole.
Discharge to a grassy area has its own geometry. Section 3.2.1.3 requires "a minimum separation of 50 feet between the discharge point to the grassy/vegetated area and the nearest storm drain or waterway", sheet flow with no runoff, dry weather, gross pollutants collected first, and only pollutants that biodegrade naturally. Section 3.1(5) rules out evaporation as a disposal method entirely, and section 3.1(12) rules out cleaning during a rain event where wash water could intermingle with runoff.
Storm drain discharge is permitted under section 3.2.1.4 only where every listed criterion is met at once, and the criteria are written to exclude chemistry rather than to accommodate it. Section 3.2.1.4 requires pH 6.0 to 8.5, temperature not exceeding 90 degrees F, conductivity less than 300 uS/cm, fecal coliform less than 150 cfu/100 mL, and "no traces of copper, phenols, surfactants, emulsifiers, dispersants, detergents, solvents, degreasers or other cleaning chemicals". Section 3.2.1.4(4) states that the option "is intended to allow for cosmetic cleaning of surfaces stained with leaves, mildew, or atmospherically deposited dusts and pollens only".
Responsibility does not sit with the crew alone. Section 3.1(11) of WQ-1 states that "As the generator of the washwater the surface cleaner is considered jointly responsible with the property owner for its appropriate disposal", and section 3.1(4) directs buyers to "ensure that the selected contractor is capable of completing surface cleaning in accordance with this guideline". Section 4(2) records that Gwinnett County maintains a "List of Businesses Capable of Collecting Surface Cleaning Washwater", supplied to the public, and states that inclusion "does not constitute an endorsement of the operator by the county". Thrare Contracting is not on that list.
Two limits on the Gwinnett material matter more than any figure in it. Section 100-21(e) of the Gwinnett County Code states that the illicit discharge article "shall apply throughout the unincorporated area of the county", so Chapter 100 does not reach Lawrenceville, Duluth, Norcross, Suwanee or any other incorporated Gwinnett city, each of which runs its own instrument. And the penalty at section 100-27(f), a fine "not to exceed $1,000.00 or imprisonment for 60 days or both", is Gwinnett County's own ordinance penalty for unincorporated Gwinnett. That figure is not a Clean Water Act penalty, and carrying it into Cobb, DeKalb, Fulton or a city jurisdiction would misstate the law in every one of them.
What chemical paperwork can a property manager ask a contractor for?
A safety data sheet exists for every hazardous chemical on a jobsite, and OSHA is the reason. Under 29 CFR 1910.1200(g)(1), "Chemical manufacturers and importers shall obtain or develop a safety data sheet for each hazardous chemical they produce or import." Under 29 CFR 1910.1200(g)(8), "The employer shall maintain in the workplace copies of the required safety data sheets for each hazardous chemical, and shall ensure that they are readily accessible during each work shift to employees when they are in their work area(s)." The standard was read 2026-09-04 from the Cornell Legal Information Institute.
Section 1910.1200(g)(2) fixes the shape of that document at 16 sections in a set order: Identification; Hazard(s) identification; Composition and information on ingredients; First-aid measures; Fire-fighting measures; Accidental release measures; Handling and storage; Exposure controls and personal protection; Physical and chemical properties; Stability and reactivity; Toxicological information; Ecological information; Disposal considerations; Transport information; Regulatory information; and Other information. Section 13, disposal considerations, is the one a property manager should read on an exterior cleaning job.
Training sits alongside the paperwork. Under 29 CFR 1910.1200(h)(1), employers "shall provide employees with effective information and training on hazardous chemicals in their work area at the time of their initial assignment, and whenever a new chemical hazard the employees have not previously been trained about is introduced into their work area."
State the limit of that rule honestly, because the limit is where a vendor questionnaire usually goes wrong. Section 1910.1200 places a duty on an employer toward employees, not a duty on a contractor toward a customer. A property manager asking for the safety data sheet and the product label for everything a crew intends to spray is asking for two documents that must already exist on the site, and a contractor who cannot produce either one has answered the question.
What sits inside a chemistry-led wash scope, and what sits outside it?
Inside the scope: product selection matched to the substrate manufacturer's own cleaning document, the registered label dilution and dwell for any product carrying an antimicrobial claim, pre-wetting and post-rinsing of planting beneath every elevation being washed, containment and recovery wherever the wash area drains toward a storm drain inlet, the safety data sheet and product label kept on site, and a walk of the finished elevation with whoever signs off.
Outside the scope, and named rather than left to be discovered later:
- Any dilution stronger than the registered label. A hotter mix to hit a tighter schedule is a violation of 7 U.S.C. 136j(a)(2)(G), so no scope prices it.
- Vehicle and equipment washing. Gwinnett County's WQ-1 definition of surface cleaning states plainly: "This definition does not include the cleaning of vehicles or equipment." Vehicle washing is a separate wastewater question with separate rules.
- Wash water containing hazardous waste. The same WQ-1 definition covers surface cleaning "where such washwater does not contain any hazardous wastes", so a surface carrying a hazardous residue is a remediation scope rather than a cleaning scope.
- Interior mold remediation. Exterior cleaning chemistry addresses growth on an exterior surface and does not address a moisture source inside a wall.
- Coatings, sealers and paint stripping. Coating work follows the coating manufacturer's surface preparation document, which is a different specification from a cleaning document.
- Sanitary sewer discharge without the property's permission. WQ-1 section 3.2.1.1(b) requires property owner permission for discharge to a sanitary sewer, so that permission is the owner's to give.
What does a contractor need from a property before the first wash?
Five items decide the chemistry before a crew leaves the shop, and a property manager can supply all five from a desk:
- The cladding, by manufacturer and product line. James Hardie, Sto, Sika LaHabra, Trex and TimberTech each publish different prohibitions, and a wall cannot be matched to a document until the wall is identified.
- Warranty status of the cladding, roof and decking. James Hardie and Trex both tie cleaning method to warranty coverage in writing.
- Where the nearest storm drain inlet sits, and whether a sanitary sewer clean-out is available on the property. Those two facts decide whether the job is a containment job under WQ-1 section 3.2.1 or a simple rinse.
- Irrigation schedule and planting locations. Beds under the elevation being washed have to be wet before the first spray and rinsed after the last one.
- Access hours and tenant notice requirements. Dwell time is measured in the 15 to 20 minute range the surface manufacturers publish, so an elevation cannot be rushed to fit a 30 minute window.
Thrare Contracting works to the published document for the surface in front of the crew and to the registered label for the product in the tank, and names both when a property manager asks which one. To discuss a specific building, schedule service online, call (678) 748-3578, or read what a commercial pressure washing or soft washing visit covers.