Cloudy windows after pressure washing: capillary intrusion and the sin of detergent runoff

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Service call I got too many times to count: a homeowner had hired a pressure-washing service to clean their siding. The siding looked great. The windows looked terrible. Hazy, milky, completely uniform across whole panes — not streaks, not spots, just a fog that wouldn't lift no matter what they cleaned with.

The pressure washing crew, at this point, was no longer answering calls.

This is one of the most consistent failure modes in residential exterior maintenance. Pressure washing siding is genuinely useful. Pressure washing siding near windows without preparing the windows first is a recipe for damage that frequently outlasts the original siding contract. I want every homeowner to know what's happening — both so they can fix it after the fact, and so they can make better decisions about contractors before the fact.

There are two failure modes. They look similar at first glance. They have different fixes.

Failure mode 1: Detergent residue from runoff

The most common version of this problem is the one with the cleanest fix.

Pressure washing siding usually involves a detergent — sometimes a sodium hypochlorite solution (essentially diluted bleach) for mold removal, sometimes an alkaline degreaser, sometimes a "house wash" mix sold by pressure-washing supply stores. The detergent goes onto the siding, dwells, and gets rinsed off with high-pressure water.

The detergent does not stay on the siding. It runs down. Across, around, through. By the time it reaches the bottom edge of a pressure-washed elevation, it has flowed across every window between the top of the wall and the gutter line. If the windows aren't masked or pre-rinsed, that means the detergent flowed over the glass, partially evaporated, and left behind a residue.¹

The resulting haze is uniform across the affected panes — distinguishing it from random spotting — and tends to be slightly opalescent, meaning it has a faint milky-blue cast in certain lighting. That cast is the optical signature of dried surfactant film at higher concentration than the trace residues from normal cleaning. It's a specific look, and once you've seen it twice, you can identify it from across the room.

I have seen this on hundreds of houses. The diagnostic is usually obvious from context (recent pressure washing) plus the uniform milky appearance. When in doubt, the alcohol test confirms it — wipe a small section with isopropyl alcohol, and detergent haze visibly clears immediately. If alcohol clears the haze, you have detergent residue.

The fix

The good news is that this is the easy problem. Detergent residue, even at the higher concentration left by pressure-washing runoff, is removable with the same tools you'd use for any surfactant residue.

My standard protocol for affected windows:

Step 1: Wash with hot soapy water. Yes, soapy water removes other soapy residue — the surfactants in dish soap (specifically Dawn) actively dissolve the dried surfactant film and lift it back into solution. One drop of Dawn per quart of warm water, applied with a clean cloth, with light agitation. This step alone often handles 70% of the haze.

Step 2: Rinse with clean water. Either spray-bottle distilled water or a hose. The point is to rinse away the soap-and-soap mixture before it dries.

Step 3: Squeegee or microfiber dry. Standard finishing technique, dry the glass cleanly while the alcohol pass (next step) is being prepared.

Step 4: Alcohol neutralization. A 50/50 mix of distilled water and 91% isopropyl alcohol, sprayed on, wiped with a fresh microfiber, and dry-buffed. This is the same neutralization pass Mara recommends in Article 009 for any surfactant residue, and it's the step that makes the difference between "sort of cleaned" and "actually cleaned."

For a typical residential job — say, eight affected windows on one elevation — this whole protocol takes about an hour. The result is identical to professionally washed windows. The haze is gone. It does not return.

Failure mode 2: Capillary intrusion under the gasket

The second failure mode is less common but more serious.

A pressure washer at residential consumer pressures (2,000–3,000 PSI) generates enough force to drive water past gaskets that ordinary rain or hose water would not breach. The water doesn't push the gasket out of the way mechanically; it gets forced into capillary spaces around the gasket-to-glass interface, where surface tension would normally exclude it. Once it's inside that capillary space, it has nowhere fast to go — the same surface tension that prevented it from entering at low pressure now prevents it from leaving.

The water sits between the gasket and the glass for days or weeks. It evaporates slowly, depositing whatever was dissolved in it (minerals, detergent residue) on the inside surface of the gasket and on the perimeter of the glass. The result is a hazy band along the edge of the affected panes, sometimes extending an inch or more into the visible glass area.²

This is harder to diagnose because it's similar in appearance to butyl migration (Article 010) or to interior IGU condensation if the haze extends far enough. The distinguishing features:

• Edge concentration. The haze is significantly worse at the perimeter and fades inward. Detergent residue from the surface runoff is uniform; capillary intrusion is edge-focused.
• Recent pressure-washing history. This is essentially required for the diagnosis. Without recent pressure exposure, this specific failure mode doesn't occur.
• Resistance to surface cleaning. Wiping the glass with alcohol or any cleaner does not affect the haze, because the haze is on the side of the glass that's inside the gasket, not on the visible interior or exterior surface.

The fix (if there is one)

This is where I have to be honest: capillary intrusion is sometimes self-resolving and sometimes not.

In maybe half of the cases I've worked, the moisture eventually evaporates on its own over a period of weeks to months as the seasonal humidity drops. Warm, dry weather speeds this. Cold, humid weather extends it. The mineral residue that gets deposited as the water finally evaporates is sometimes light enough to be visually unnoticeable; sometimes it leaves a permanent edge haze that the homeowner lives with.

In the other half of cases, the moisture either doesn't evaporate fully (because the gasket-to-glass interface is too well-sealed for vapor escape) or it deposits enough mineral residue that the resulting haze is permanent. At that point, the only fix is removing and reseating the gasket, which is a significant repair — typically requires a glazier, and depending on the window construction may involve full IGU disassembly or replacement.

For early-stage capillary intrusion, my recommendation is patience. Wait two to three months. Run a dehumidifier in the affected room if you have one. Open the windows when humidity is low. If the haze is still there after three months, get a professional opinion on whether reseating the gasket is feasible.

For long-established capillary intrusion (older than six months) or for cases where the gasket itself has been degraded by the pressure exposure, replacement of the IGU or the affected window is sometimes the more economical path. The repair cost frequently approaches replacement cost on older windows.

How to tell which problem you have

The simple discriminator is location.

Detergent residue: uniform across the entire pane, sometimes worse at the bottom (where runoff pools longer), but present everywhere. Removable with cleaning.

Capillary intrusion: concentrated at the edges of the pane, fading toward the center. Not removable with cleaning; the affected zone is on the wrong side of the gasket.

In practice, after extensive pressure-washing damage, I often see both problems on the same windows. Detergent residue across the visible glass surface, plus capillary intrusion at the perimeter. The detergent portion can be cleaned. The capillary portion requires waiting and possibly replacement.

If your post-pressure-wash haze has both characteristics, treat the cleanable portion first. The remaining edge haze, after cleaning, is your capillary diagnosis. From there, you decide whether to wait, repair, or replace.

Why this happens at all

The honest answer is that the pressure-washing industry is uneven on training. There are genuinely excellent pressure-washing contractors who understand glass, who mask windows before working anywhere near them, who use detergents that are explicitly safe for glass exposure, and who follow up with a proper rinse. There are also a lot of operators who don't, and the difference between the two is often invisible to homeowners hiring on price.

The proper protocol for pressure-washing siding near windows involves at least these steps:

1. Pre-wet the windows with clean water before applying detergent to the siding. This dilutes any incidental runoff and prevents the detergent from drying on the glass.
2. Apply detergent in controlled vertical zones, working from top to bottom, rinsing each zone thoroughly before moving down.
3. Avoid direct high-pressure spray on windows, gaskets, or seal lines. Lower pressure (or use of a low-pressure soft-wash applicator) is sufficient for siding cleaning and dramatically reduces the risk of capillary intrusion.
4. Rinse all glass thoroughly with clean water at the end of each elevation, before any drying can occur.
5. Squeegee or rinse-and-dry the windows as a final step, before leaving the site.

A contractor who does these things well will leave your windows in better condition than they were before the wash, because the rinse-and-dry step at the end is essentially a free window cleaning. A contractor who skips these steps will leave you with the problems described in this article.

Hiring a pressure-washing contractor: ask whether they mask or pre-rinse windows before working near them. The answer should be specific and confident. "We're careful around windows" is not the right answer. "We pre-rinse, control runoff, and finish with a clean-water rinse on every elevation" is the right answer. The difference is the difference between a $400 wash that's fine and a $400 wash that costs you $2,000 in subsequent damage.

What to do if it's already happened

A practical action plan, in order:

1. Don't panic. The detergent residue version is fully fixable and not particularly hard. Read your situation correctly before assuming the worst.
2. Document the damage. Photos in good light, before any cleaning attempts. If you end up needing to argue with the contractor or pursue any kind of recovery, photos taken within 24-48 hours of the work are your strongest evidence.
3. Try the simple fix first. Hot soapy water with Dawn, alcohol neutralization pass. If this resolves the haze, you have only detergent residue, and the matter ends here.
4. If haze remains at the edges, identify capillary intrusion and decide on a wait. Two to three months of monitoring before paying for any repair work.
5. Document the contractor. If the work was substandard, leave honest reviews. Other homeowners reading those reviews are who I'm writing this article for as much as you are. Pressure-washing contractors who damage windows continue damaging windows until the market catches up to them.

A closing thought

Pressure washing your house is a worthwhile thing to do every few years. So is window cleaning. The two activities should be sequenced and performed by people who understand they affect each other. The crews that do this well are out there. They tend to be the ones who quote slightly higher because their work takes longer and uses more setup. They are worth the difference. The savings on a low-bid pressure-washing contract evaporate the moment you have to pay someone else to fix what they broke.

I'd rather you read this article and never need it. But if you're reading it because you already need it: the diagnosis is what determines the fix, and the diagnosis is usually obvious once you know what you're looking at.

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Footnotes

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Sources

• Pressure Washing Resources Association, Best Practices for Soft Wash and Pressure Wash Siding Maintenance, 2024.
• ASHRAE, Building Envelope Moisture Management, 2022 technical document.
• Cardinal Glass Industries, Care and Cleaning Recommendations for LoĒ Coated Glass, 2024.
• Insulating Glass Manufacturers Alliance, Field Guidelines for Pressure Washing Near IGU Installations, 2023.
• The Soap and Detergent Association, Surfactant Chemistry: A Technical Reference, 6th edition, 2021.

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About the author

Jan Davenport ran a six-truck residential window cleaning route in suburban Detroit for eleven years before selling the company in 2023. He now writes full-time for Window Washing Guide, where he covers homeowner-facing diagnostics and the practical fieldwork that keeps service professionals employed. His writing has appeared in Pro Window Cleaner Magazine and the IWCA quarterly. He still washes the windows on his own house, badly, because he is no longer trying to impress anyone.

All articles by Jan → · Editorial standards →

Footnotes

1. Pressure washing detergents are formulated for high-effectiveness on siding stains (mildew, algae, oxidized paint), which means they contain higher concentrations of active surfactants and, often, sodium hypochlorite or alkaline boosters. Residential glass cleaners are formulated to leave minimal residue at the dilutions actually used; pressure-washing detergents are formulated for cleaning power and assume a thorough rinse. When the rinse doesn't happen on the glass surface, the residue is correspondingly heavier. ↩

2. The capillary intrusion phenomenon is not specific to pressure washing — it can occur during driving rain at high wind speeds, or during ice damming where meltwater is forced under flashing — but pressure washing is the most reliable way to produce the failure on demand at residential pressures. Some IGU manufacturers' installation specifications explicitly warn against pressure washing within a specified distance of the glass for this reason. ↩