White blotched vinyl siding (C) Daniel Friedman Hagantown Poughkeepsie NY Vinyl Siding Cleaning Procedures
How to clean vinyl siding & avoid leaving stains

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Vinyl siding stain cleaning procedures, chemicals, products:

What methods are recommended by vinyl siding manufacturers and by siding cleaning companies for cleaning dirty, stained, or oxidized vinyl siding?

What goes wrong during siding cleaning procedures: new stains may appear, water can get blown into building walls, shrubs might be killed, ground or nearby waterways might be contaminated if the manufacturer's instructions are not followed.

This article series discusses common causes of stains or discoloration found on vinyl building siding. Distinguishing the type of stain found on siding is useful in deciding on the cause and thus the cure or prevention of staining

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Avoid Stains or Damage Caused By Vinyl Siding Cleaning

Vinyl siding spotty stains appeared after cleaning (C) BDThese vinyl siding stains and vinyl siding cleaning diagnostic questions & replies were posted originally at VINYL SIDING STAINS

Watch out: when power-washing siding do not spray "up" such that water is forced underneath or behind the siding or you may cause serious leaks into building walls, in turn cause wet insulation or wall cavity mold contamination.

Photo: spotty stains appeared on vinyl siding after it was cleaned by a siding cleaning company.

Question: how can I remove the spots left on my siding after I had it cleaned?

Just sent you an e mail about my problem and this is the follow up pictures. We will have to reside our entire house if this issue is not solved as it is right by our doorbell and front door and it extensive in this area.

I would really appreciate your ideas as to the caused. I have contacted the company to have it cleaned again and it did not change. - Anonymous by private email 2017/06/10


I can't say for sure what the problem is with the yellowish stains I see on white vertical trim and darker stains I see on grey-beige vinyl siding in your photo. I suspect that a cleaner containing a bleaching agent may have been sprayed or over-sprayed onto a surface while working nearby, then let sit too long without actual washing-off.

I have read but don't know from direct experience that some vinyl siding, particularly darker colors, vary in chemical composition and thus in their susceptability to chalking and staining before and as a result of washing. I also read that some less-costly vinyl siding products are a laminated product whose surface color is just a thin layer that is more-easily damaged by cleaning agents.

That is to say some siding cleaners blame the product for some stain issues and suggest that you check the siding warranty.

I would try some local spot cleaning in a less-obtrusive location to see if a household cleaner, scrubbing, or a cleaner suggested by your contractor get rid of the trouble. If the siding surface was oxidized and chalky you may be able to reduce the yellow blotches by gentle scrubbing with a properly-diluted bleaching cleaner.

General advice when cleaning a surface to try to remedy a dirt or stain problem: always try the least-aggressive method and least-aggressive cleaner (start with plain water or plain water and a power washer or scrub brush) first.

When stains appear after washing, sometimes waiting a few days for the surface to dry thoroughly may show that the stains mostly disappear; (On the other hand I've had complaints from readers that some stucco siding products had stains that reappeared every time it rained.)

When the coating on siding is oxidized some siding cleaners use a cleaning solution that contains potassium hydroxide (KOH) or alternatively a butyl-based cleaner to emulsify the oxidized particles on the siding surface. Basically you'd need at least a cleaner that includes a "surface debris surfactant" to clean such siding.

Watch out: I am NOT prescribing ANY specific treatment for your home, as no one in their right mind could try to do so based on one photo and an e-text message. But these are options among those you might want to discuss with your siding cleaning contractor.

So IF the stains were - by luck - principally in the oxidized layer of a siding surface, then it may be possible to remove or significantly-reduce them by this more labor-intensive (and more expensive) cleaning process.

Oxidized siding surfaces is a condition you can usually detect by noticing a chalky deposit on the surface that can be smeared with a thumb or scrubbed away with a soft brush and water or water + detergent. Oxidation of the siding surface (or of paints on surfaces) is a result of sunlight (UV exposure) that breaks down chemicals in the surface.

An experienced siding cleaning company might know to warn the customer if they see oxidized siding surfaces that simple "cleaning" won't be effective and that a more costly and troublesome "siding restoration" procedure involving more-careful cleaning will be needed. If I were the contractor I'd warn, in writing that oxidized siding presents special and extra risks of blotching, spotting, streaking stains following cleaning efforts.

I also warn that on some older aluminum siding that was oxidized I've seen cleaning remove all of the paint pigment leaving shiny aluminum!

More Information to Help Diagnose Post-Cleaning Stains Appearing on Vinyl Siding

Bottom line: my OPINION is that bleach-caused spots on vinyl siding and trim won't be removed once a bleaching agent sat long enough to cause yellowing and that the only option to fix what is primarily a cosmetic problem is either painting the siding or re-siding the side of the home with the most significant damage.

Proper Procedures for Cleaning Vinyl Siding

The Vinyl Siding Institute offers advice on cleaning vinyl siding, recommending basically soft-brush scrubbing, bottom-up, and gives several documents that describe cleaning procedures against which you could review what your cleaning company did:

The Vinyl Siding Institute's Vinyl Siding Installation Manual (includes cleaning advice) Contact:
Jeff Smith, Director, Communications, Vinyl Siding Institute Tel: (202) 587-5109 Email: Website:


Although vinyl siding will get dirty, like anything exposed to the atmosphere, a heavy rain will do wonders to clean it. Or, it’s possible to wash it down with an ordinary garden hose. If neither rain nor hosing does a satisfactory job, follow these simple instructions:

  1. Use an ordinary, long-handled car washing brush. This brush has soft bristles, and the handle fastens onto the end of the hose. It allows the siding to be washed just like a car. Avoid using stiff bristle brushes or abrasive cleaners, which may change the gloss of the cleaned area and cause the siding to look splotchy.
  2. To remove soot and grime found in industrial areas, wipe down the siding with a solution made up of the following: n 1/3 cup (0.08 liter) powder detergent (e.g., Fab®, Tide®, or equivalent powder detergent)* n 2/3 cup (0.16 liter) powder household cleaner (e.g., Soilax®, Spic & Span®, or equivalent)* n 1 gallon (3.8 liters) water
  3. If mildew is a problem, use the solution previously mentioned, but add 1 quart (0.95 liter) liquid laundry bleach.

    Note: actually there is no true "mildew" on buildings. Mildew, a subset of molds, is an obligate parasite that only grows on living plants. If you see moldy-looking stuff on your siding, it's mold. See MILDEW PHOTOGRAPHS BUILDINGS ? - Ed.
  4. When washing down the entire house, start at the bottom and work up to the top in order to prevent streaking.

The article also includes suggested cleaners for specific stains. VSI Vinyl Siding Installation Manual (2017).

Avoid These Problems When Cleaning Vinyl Siding

Vinyl siding spotty stains appeared after cleaning (C) BDIf portions of the siding are discolored even after drying completely there can be various causes, not all of which would be the fault of the cleaner nor cleaning process.

  1. Fault of the cleaning process: not following the cleaner instructions such as how long a cleaner is left on the surface before rinsing, or using in hot or sunny conditions, or not applying in the proper dilution or concentration, or not applying using the proper method.
  2. Fault of the cleaner: probably none if you selected a cleaner that is intended for use on vinyl siding and if the cleaner is used as directed, but some contain bleaching agents that will affect different siding surfaces differently depending on the condition of the siding - see next comment
  3. Fault of the siding or pre-existing conditions: siding conditions vary, for example just restricting our discussion to vinyl siding, siding in areas exposed to more sun may be more photo-oxidized;

    the extent of removal of oxidized material may vary depending on the cleaning method and variations in its application (spray distance, scrubbing vigour, exposure to sun and wind and temperature variations) as well as to what dirt or soiling materials are on the siding surface (grease vs. dust, algae vs. stains).

From the example siding cleaning products below you'll see that different manufacturers take varying approaches to the chemistry, use, and suitability of their cleaning products.

Watch out: bleach "stains" on all sorts of siding are a common siding-cleaning issue. Marks may appear as overspray spots that the cleaning contractor didn't notice and that thus left a bleaching cleaner sitting too long on the surface.

I see this problem more often when a siding cleaning contractor, working on area A, allows overspray of their cleaner to splash onto a nearby area B without notice, particularly when working in hot sun or on a dry windy day. The overspray droplets may dry quickly and not even be noticed by the cleaner during the job. Later as the bleaching cleaner sat longer in some areas than others, yellowing marks of bleached surface may appear.

Marks may also appear as run-down stains, vertical drip marks if during cleaning an upper area of siding the cleaner+cleaned-surface materials ran down to lower siding where it sat too long before rinsing.

Watch out: also for using high-pressure power washers when cleaning siding. Using pressures over 100 psi increase the chances of damage to the siding, power-washer cut marks on softer siding materials (wood), and of blowing water up under the siding and into building walls where it soaks insulation and invites a wall cavity mold contamination problem.

In addition, blowing a power wash up into the siding means that even after the washing contractor thinks they're finished cleaning and rinsing an area of siding there will be additional run-down of cleaning solution that was up inside the siding and that later drains out of siding weep/drain openings where it dwells on the siding surface causing a streaking problem.

This is not an explanation of the spotty stains described earlier in this article: those are probably the result of cleaner overspray that was left on the surface too long.

More examples of stains and problems following cleanign of vinyl siding are at VINYL SIDING STAIN CLEANING FAQs.

Siding Cleaning Products & Their Chemicals

Here we describe cleaners, their main ingredients, and the basic chemical properties of those ingredients. Some popular cleaning approaches and products used for vinyl siding cleaning include the following:

Safest Cleaners for Vinyl Siding

  1. Safest: start with plain water and low power washing and soft brush scrubbing
  2. Second-Safest: mild dish detergent and soft brush scrubbing with plenty of rinsing. Suitable for lower-grade siding products or for any siding product whose manufacturer specifically says DO NOT USE BLEACH PRODUCTS when cleaning the siding.
  3. Safe: water + vinegar solution (vinegar is a mild acid) in a 30% vinegar solution in clean water.
  4. Murphys Oil Soap® (I've had good results with this product and a soft scrub brush)
  5. Windex® (window cleaner) (I've had good results with this product too - watch for streaking, spray & soft-brush & rinse promptly)

Following the use of a siding cleaner with low pressure washing or soft brushing is usually effective.

Bleaching Cleaners for Vinyl Siding

  1. Basic: 4-7% bleach solution + detergent & soft scrub brush, keeping surfaces wet during cleaning, rinsing thoroughly, taking care to NEVER let bleach solution run down on siding and sit there; Permitted by some siding manufacturers.
  2. Fantastik (VSI recommended for stubborn stains)

Siding Cleaners to Avoid - These Will Damage Sidiing

Never use these products on vinyl siding:

Properties of Siding Cleaners

Watch out: some of these are dangerous chemicals and must be used following the manufacturer's directions and with proper protective gear.


Continue reading at VINYL SIDING STAINS - home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see VINYL SIDING STAIN CLEANING FAQs - questions & answers about stains appearing after cleaning vinyl siding

Or see these

Vinyl Siding Articles

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VINYL SIDING CLEANING METHODS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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