Soft Wash House Procedure Standard

Purpose

A soft wash removes mold, algae, and mildew from siding by chemistry and dwell time rather than by pressure. That works exactly once the mix, the coverage sequence, and the dwell are right, and it fails in a specific direction when they are not: too weak leaves the growth's root intact so it returns in weeks instead of a year or more, too strong or dwelled too long streaks or bleaches the surface, and drift onto a neighbor's car, deck stain, or garden turns a clean job into a claim. This standard fixes the mix to a stated concentration, the application to a wet-edge rule, and the chemical control to a named response, so the outcome does not depend on which tech ran the truck that day.

Scope

Covers the standard soft wash of exterior siding on residential and light-commercial buildings up to two stories, using a sodium hypochlorite (SH) based house-wash mix delivered at soft-wash pressure through a skid or an injector. Site prep is owned by the Pre-Wet and Plant Protection standard, and rinse-off plus inspection are owned by the Rinse Sequence and Final Inspection standard; this SOP calls both as handoffs and does not re-derive them. Technique variance by siding material is owned by its own how-to.

Out of scope: roof soft washing, which runs a different mix, dwell, and fall-protection profile, and hardscape or driveway cleaning with a surface cleaner, which is a hot-water or straight-pressure service, not a soft wash.

Roles and the handoff between them

Before the wand comes off the truck

Sodium hypochlorite burns skin and eyes and is never mixed or staged with an acid or ammonia-based product. Wear chemical-resistant gloves and eye protection while handling concentrate, and keep an oxalic-acid rust remover, an acid-based brightener, or an ammonia-based glass cleaner on a separate cart, mixed in a separate tank, hose flushed between chemical types. And if that does not hold, a sharp chlorine or ammonia-like odor at the mix station is a gas release: shut the pump down, move everyone upwind to open air, do not go back to close a valve, and call it in before anyone re-enters.

Confirm the discharge point before the first drop hits the ground. Wash water carrying SH or surfactant that reaches a storm drain is treated as an illicit discharge under the federal storm sewer framework (40 CFR 122.26) in most municipalities; the containment method your local stormwater authority requires, whether that is berm-and-vacuum, diversion to a vegetated area, or a permitted release, is set locally, not by this standard, so confirm it before the first job in a new service area.

A wand-mounted extension reaches most two-story eaves from the ground; a ladder is the exception, not the routine. Where the layout still needs one for a gutter check or a fixture out of wand reach, use a setup that meets 29 CFR 1910.23 for portable ladders, a 4-to-1 pitch, extending at least 3 feet above the landing, and lean it against the wall framing, never against the gutter.

The procedure

1. Confirm site protection is complete before any chemical is mixed. Get sign-off that the Pre-Wet and Plant Protection standard has run: beds soaked, sensitive fixtures covered, and anything isolated for the job (pool circulation, irrigation controller) shut off and tagged. Acceptance: a checked handoff on the ticket, not a verbal "we're good." Wrong looks like a tech starting the mix while the second tech is still soaking the last bed. Stop rule: no chemical goes into a tank until the handoff is checked. Hazard: none introduced here, but skipping this step turns every hazard below into a plant-kill or pool-contamination event instead of a controlled one.

2. Mix to the standard starting ratio and log it before it leaves the tank. Using a 12.5 percent sodium hypochlorite source, mix roughly 1 part chemical to 20 parts water plus the labeled dose of surfactant, which lands at about 0.6 percent available chlorine at the surface, a reasonable starting point for mild to moderate growth on painted or vinyl siding; heavier growth shifts the ratio toward 1 part to 15, about 0.8 percent, rather than stacking extra dwell time on a weak mix. Acceptance: the ratio logged on the ticket against the source strength it was built from. Wrong looks like "about half a jug" with no ratio anyone could repeat. Stop rule: if the source concentration on the jug is unlabeled or unknown, do not guess it, get the label first. Hazard: concentrate splash while pouring; gloves and eye protection go on before the cap comes off, not after the first splash.

3. Set the application pressure to soft-wash range and confirm the path. Deliver the mix through the skid's dedicated low-pressure line or a wide-pattern nozzle off the machine, well under 100 psi at the surface, the same ceiling the industry's own working definition of "soft wash" uses; running the main pump's full output through a narrow tip is pressure washing with chemical added, not a soft wash, and it is the fastest way to drive water behind trim and siding laps. Acceptance: pressure confirmed at the tip, not assumed from the machine's rated output. Wrong looks like a tip swapped mid-route for a faster job that quietly puts the crew back over 100 psi. Stop rule: if the low-pressure path is not confirmed, do not start on the wall, fix the setup first. Hazard: chemical under pressure at the nozzle; keep the tip clear of your own face and any bystander's line of sight while checking the setup.

4. Apply bottom to top, keeping a wet edge. Work each elevation from the bottom up in overlapping passes, re-wetting the leading edge before it can dry, rather than starting at the top and letting runoff carry chemical down onto dry siding below. Acceptance: full, even coverage with no section left to dry before the next pass reaches it. Wrong looks like a bright streak or blotch forming where chemical dried unevenly before the rest of the wall was covered. Stop rule: the moment a dry streak starts forming, re-wet that section immediately rather than pressing on to the next elevation. Hazard: overspray and drift onto skin, landscaping, and neighboring property; check wind direction before starting each elevation and hold the windward side if gusts are carrying mist past the property line.

5. Hold dwell inside the standard window and do not let it dry. Give the mix 5 to 15 minutes depending on soil load and conditions, re-wetting any section that starts drying before the window closes; a hot, direct-sun day pushes toward the short end with more re-wetting, a cool or shaded day allows the long end. Acceptance: the whole elevation still visibly wet when the dwell timer closes. Wrong looks like a chalky white haze where the chemical fully dried and crystallized on the surface. Stop rule: any section drying before the rinse crew reaches it gets re-wet on the spot, it does not wait for the scheduled rinse. Hazard: continued skin and eye exposure through the re-wetting passes; gloves and eye protection stay on through this step.

6. Hand off to the Rinse Sequence and Final Inspection standard. Rinse, inspection, and discharge handling for this job belong to that standard, not this one; confirm it has run and been signed off before the ticket closes. Acceptance: a completed rinse worksheet attached. Wrong looks like a crew leaving before the rinse sign-off exists. Stop rule: the job is not complete without it.

7. Restore anything isolated for the job and verify it. Turn the pool pump and irrigation controller back on if either was shut off in step 1, and confirm each is actually running, pump primed and circulating, irrigation zone cycling on a manual test, before the truck is packed. Acceptance: both confirmed running, not just switched back on. Wrong looks like a pool pump flipped on but airlocked, or a controller powered but still on the wrong schedule. Stop rule: do not leave the site with an isolated system unverified. Hazard: none from this step; the hazard it closes out is a customer discovering a dead pool pump or a flooded bed days later with no tech on site to trace it to.

The record this produces

A mix-and-application worksheet on the ticket:

• Mix log: source strength, ratio used, and whether the growth load moved it off the standard ratio.
• Pressure check: which delivery path was used and the confirmed tip pressure.
• Coverage notes: any section re-wet for drying, and which elevation.
• Isolation log: what was shut off in prep and confirmed restored at close.
• Handoff confirmations: pre-wet sign-off and rinse sign-off, both checked before the ticket closes.

This is the record a callback gets checked against: a mix ratio nobody logged cannot be defended, and an isolation nobody logged is the pool pump a customer finds dead a week later with no name attached to the job.

One run of this procedure, filled in

Two-story vinyl-sided house, moderate green algae on the north-facing gable, mid-morning, mild and overcast.

• Step 1: pre-wet and protection signed off, beds soaked, pool pump and irrigation controller both confirmed off and tagged.
• Step 2: 12.5 percent SH source, mixed 1 to 20 with surfactant, logged as roughly 0.6 percent at the surface. Growth was moderate, not heavy, so the standard ratio held.
• Step 3: skid's low-pressure line confirmed, tip pressure checked well under 100 psi.
• Step 4: north gable started bottom to top on the shaded side first.
• Step 5: this step failed on the south-facing return wall. Full sun had already dried the leading edge of one pass before the next pass reached it, and a faint white haze started forming at the transition. Stop rule taken: that section was re-wet immediately, dwell restarted on it, and the crew shortened dwell to the low end of the window on the rest of that elevation to keep pace with the drying rate.
• Step 6: rinse and final inspection standard run and signed off, no haze remaining after rinse.
• Step 7: pool pump switched back on and confirmed circulating; irrigation controller powered on and cycled through one zone manually to confirm the schedule was intact.

The south wall near-miss is why step 5's stop rule is a live check during application, not a pass or fail read at the end: caught mid-pass, it cost one re-wet; caught after a full dry, it would have cost a re-mix and a second dwell cycle on a wall already rinsed once.

References

• 40 CFR 122.26, the federal storm sewer discharge framework, which most local stormwater ordinances enforce for wash-water containment; confirm the accepted method with your municipal authority.
• 29 CFR 1910.23, portable ladder requirements, for the exception cases where wand reach is not enough.
• See related: Pre-Wet and Plant Protection Before a House Wash, Rinse Sequence and Final Inspection Standard, Soft-Washing Technique by Siding Material.