White stains on asphalt shingle roofs in New Mexico (C) InspectAPedia & JMWhite Stains on Roof Surfaces
How to diagnose & remove white staining or deposits on various roof types

  • WHITE STAINS on ROOFS - CONTENTS: diagnose & remove white stains on roofs white & deposits on roof shingles, slates, wood roofs with white stains from various causes
  • POST a QUESTION or READ FAQs about how to determine the source of white or light colored stains on building roofs & how to remove stains from roof surfaces

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White stains on building roofs: this article describes the causes & cures for white stains or white deposits on building roofs. We describe common causes of white blotches or staining on roofs of different materials: asphalt shingle, wood shakes or shingles, stone roofs & slate roofs.

We discuss roof cleaning approaches using chemicals and the most gentle possible means so as to avoid damaging the roof and to reduce the risk of chemical burns or of building or plant damage from chemical wash-down onto lower surfaces during the roof cleaning process. Page top photo of white staining on a roof in Albuquerque NM courtesy of reader Joe Miceli, Clean Right Commercial, and Residential Pressure Washing Email: - 2013

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White Stains on Roof Surfaces: a catalog of roofs & white stains, causes & cures

Closeup of white stains on asphalt shingles in Albuquerque NM (C) InspectApedia & JMArticle Contents:


White Stains from Paint Spills on Roofs

First let's get this out of the way. We adapted the following two photographs of white blotchy roof stains from an advertisement in an Air New Zealand flight magazine. At below left the ad section showed white roof staining that was unexplained and that no doubt escaped the interest of the ad copywriter.

White roof stains traced to paint spill (C) adapted from Air New Zealand flight magazine 2014 White roof stains traced to paint spill (C) adapted from Air New Zealand flight magazine 2014

But a closer look at the same advertising photograph of two people sitting on a roof (don't ask what they were doing up there in the New Zealand sun) shows (at above right) what is rather evidently a white splash that looks like nothing other than a spill of white paint on the roof. A Kiwi would have figured this out right away.

White Stains on Asphalt Shingle Roofs

Below we report on steps to diagnose the source of white stains deposited on an asphalt shingle roof, followed by methods used to remove the white material - probably calcium & magnesium salts deposited from a draining or leaky swamp cooler.

Roof mounted air conditioner condensate drain spilling onto roof (C) Daniel Friedman White area around chimney is not a roof stain (C) Daniel Friedman

Spilling A/C condensate onto a rubber roof near a drain is not likely to be a roof stain issue but the same spillage on an asphalt shingle or roll roofing surface may lead to algae stains.

Watch out: the apparent "white stains" around the chimney shown at above right are not a roof stain at all. Rather you are seeing an area of "not stain" where runoff metal salts from the aluminum chimney flashing retarded the growth of a roof algae or fungus.

Hard water calcium stains on asphalt shingle roofs

But water draining or leaking from a rooftop mounted evaporative cooler or "swamp cooler" is more of a problem, as we illustrate below.

Photo of an evaporative cooler or swamp cooler in Tucson (C) Daniel Friedman Closeup of white stains on asphalt shingles in Albuquerque NM (C) InspectApedia & JM

Reader Question: How to remove hard water/calcium stains from roofs with asphalt shingles.

I am not having any luck trying to determine how to remove hard water/calcium stains from roofs with asphalt shingles. But most importantly, do not know what type of chemicals are best suited to clean these stains. I have been told to use everything from oxalic acid to bleach. That is why I have turned to you. Can you please help me?

I would appreciate any comments or suggestions, and if possible, chemical applications and chemical supplier contact information. - Joe Miceli, Clean Right Commercial, and Residential Pressure Washing Email: Albuquerque NM 10/22/2013 [1]


Before pretending to offer a solution let's be sure we've got the problem right. I am surprised to read about hard water stains on a roof - where is the water coming from? Are you sure you have correctly identified the stains and their cause? If not, jumping to a solution sounds risky..

Reader Follow-up:

White stain material found on asphalt shingles (C) InspectApedia - & JMI am confident I have diagnosed the problem correctly. A lot of homeowners here in Albuquerque have swamp coolers--water cooled air conditioners--on their roofs.

The staining I have mentioned is directly connected to hard water leaks from these units; hence, the white staining.

I am trying to determine the best chemical solution to use to remove these stains and not a single person I have spoken to has given me a definitive answer.

I clearly value and appreciate your input. Can you suggest a chemical application to remove these ugly white stains prevalent here in ABQ?

Reply: Start Removing White Roof Stains Using the Least-Aggressive, Safest Method - Vinegar Compress

OK now I've got it. Please send me some sharp photos of the stained areas and the swamp cooler - indeed I've looked at this topic in Tucson.

Watch out: don't do anything drastic before we've gotten a bit further in discussion. You don't want to ruin the shingles nor stain and mess up building siding nor contaminate the soil or kill plants around the house with an unnecessarily aggressive chemical treatment.

I am curious about why the white stains are off at roof center and not directly below the swamp cooler.

Anyhow, I would first try a vinegar solution. That is the least aggressive liquid to use, least likely to damage the roof, and least toxic on the ground. Start with maybe a gallon of supermarket white vinegar, diluted 50:50 with water. Pour it onto the white area and let sit - it will probably fizz. Then wash down the roof with plain water, being sure to wash off plants and also any siding that gets wet.

Reader-Follow-Up: White roof stains traced to previous generation of cooling equipment: swamp cooler

I passed by this home today and also asked myself why the water stain is not lined up with the cooling system. I assume--after considering that question today--the answer may be that the current cooling system, on the right of the stain, may have been a new system and not the one that may have been sitting where the stain is. (The current air conditioner on this roof is NOT a swamp cooler; it's refrigerated air--which does not have the water leakage). Hence my assumption.

Anyway, I think that explains it. Plus, there are many homes here who have swamp coolers on the roofs and correlated white stains directly beneath them--so logic tells me it must be the hard water leaking from the swamp coolers.

At any rate, I cannot wait to get up on a roof to test vinegar solution on one of these stains. I am not a gambling man but if I had to I would bet your pretreatment is definitely going to work. Who would have thought vinegar would do the trick? I am so excited. I can't wait to try your treatment out. I have asked so many so-called roof experts and chemical suppliers about this and they were all puzzled.

At any rate, I will definitely send you before and after photos of the first stain I attempt to clean. If this works, I will be cleaning a lot of roofs this spring as I am starting up a pressure washing business.

Reply: Try stain removal chemicals on a small safe area first

White stain material found on asphalt shingles (C) InspectApedia - & JM TO be safe, try a small area of the roof first, and have a garden hose handy; you should be ok - we're not doing anything too dramatic. The single most important point, by far, over all, is don't fall off the roof.

Reader follow-up: On roof vinegar wash not adequate to remove calcium stains

Absolutely. There are shoes specifically designed to prevent falls called "cougar paws." I just wanted to give you a heads up on my latest attempt to clean the hard water stains from asphalt shingle roofs. I tried the 50/50 dilution of vinegar in water and it did not do anything.

... One thing I noticed is that the tiny granules on the shingles seem to be almost dyed the color of the calcium!

And so I think what might be necessary is to find a more aggressive chemical that can completely remove the white stains from the granules overall.

In any event I tried 2 successive treatments and rinses and of course as I indicated neither one of them were successful.

That said I am attaching a few photographs to give you an idea of what the granules look like that seemed to be almost bleached or dye white by the calcium and water from the swamp cooler.

If you have time and you can give me another option or perhaps direct me to someone who might be able to help me with this perplexing issue I would greatly appreciate it.

Reply: Attacking white mineral deposits on asphalt shingles using stronger acids

Effloresence in the microscope (C) Daniel Friedman The thing is, you can go to some much stronger stuff like muriatic acid (which is DANGEROUS don't get it on skin or in an eye) but you'll have to be johnny-on-the-spot with rinsing any building or plants that get the acid on them; and it might eat an aluminum gutter or its paint coating too.

Photo at left: granules of mineral efflorescence under our lab microscope. Details are

Muriatic acid is commonly sold in building supply stores as a masonry cleaner; it's much stronger than vinegar. HCL or hydrochloric acid might also be used.

Reader follow-up:

Great; will do. I am determined to get a solution that works. How long do you suggest I let the muriatic acid sit on the shingle.

And what do you think about what I said regarding the granules appearing to be dyed and completely whitened by the calcium staining.

I guess what I am asking is this: do you think if they have been completely bleached by the hard water that they can still be cleaned by a muriatic based pretreatment.

And by the way, when you say experiment, should I just go ahead and try the muriatic acid without a dilution? Will it burn a hole through my plastic spray bottle?

Reply: Mild or low-concentration roof cleaning acids require more time than stronger more dangerous chemicals

As long as we are convinced that the granules are colored by a deposit of white calcium-like mineral left from an on-roof swamp cooler, then in effect that should be a surface coating, and should be removable.

Pretty much all roof shingle mineral granules are produced by one company (3M if I recall correctly), and are colored-through. But being minerals themselves, the granules may indeed bond well with a calcium layer.

Power washing or scrubbing will, as you've probably read, damage a roof.

But usually an acidic bath will remove a calcium layer. For obvious reasons I like to start with a mild, safe acid like vinegar. A towel soaked with vinegar and left overnight on the white shingles might work without having to resort to more dangerous and difficult acids like muriatic.

When I have used muriatic right from the bottle it was on masonry; in contact with calcium and other debris (fresh mortar) the acid bubbles and fizzes. I wash it off of masonry in 3-5 minutes.

But if you have the time and are willing, try an overnight soaking with vinegar leaving a towel, soaked with vinegar on the roof stain. I doubt that the vinegar will change the non-white-stained granules, and it won't risk harming roofing, nor other building materials.

Reader follow-up: vinegar compress not practical

It would not be practical to have a towel soaking on the shingles overnight for two reasons: One, the stained areas are generally fairly large; and two, because it would take too much time to clean the targeted areas. (I perhaps should mention I am starting up a cleaning business here in Abq. to pay the bills, and discovered calcium stained roofs may be a good niche market). Hence, my desire get a cleaning application that will work.

At any rate, I am still hopeful I can get a solution or pretreatment application that is fast and effective.

Your suggestions are very helpful and the time you are taking to discuss this topic with me is much appreciated.

I have spoken to someone or should I say communicated with someone who indicated bi carbonated water maybe a viable solution.

Yes. Hi pressure could cause damage. Agreed.

Reply: will carbonated water or seltzer remove white mineral deposits from asphalt shingles?

I'm doubtful but it doesn't hurt to try seltzer on a white stain as it's such a mild treatment. I have used simple carbonated water to clean white salts from battery terminals. Acidic carbon dioxide solutions have been used for stain removal (see Dunsmore citation below). I'm not optimistic that it has the strength to affect the roof, but hell, give it a try.

I went to Muriatic acid (or alternatively to HCL hydrochloric acid) with reluctance as these are dangerous chemicals to mess with - you can get a bad burn.

But the chemistry of carbonated water is a milder than what you already tried (acetic acid or vinegar). Certainly pouring soda water on the roof won't hurt a thing. In a pinch I've used Coke or Pepsi, followed by a water flush to get rid of the sticky mess.

Reader Follow-Up:

Just a quick update. I attempted a muriatic acid solution, beginning with a pint to a gallon of water, let it sit on the shingles and then rinsed. Not much of a reaction, but a slight lightening.

I then used the same process, this time increased the acid to two pints to a gallon. Again progressive lightening.

On my final application, I went all out and added two quarts plus of acid to about a half gallon of water--but again was not successful.

My opinion: since the stains are definitely lightening a bit, I obviously have to move to a more potent/aggressive chemical.

Note: I agitated the acid on each application with a good stiff brush and let it sit on the shingles for 15 minutes before I rinsed during each attempt.

I am sure the stains can be removed, however, there is no way I can make any money cleaning these types of stains if I have to perform multiple chemical applications. I have to find a chemical formula that will remedy the problem on the first, or at the least, second application.

If you have any suggestions, please advise at your convenience. - J.M. 11/13/2013

More Options for Removing White Stains, Lime and Scale Deposits from Roofs - More about the Chemistry of Lime Scale Deposits & De-Liming Cleaners, Chemicals, Treatments

Lime scale fragments from a water heater (C) Daniel FriedmanYou are quite right. I can suggest a few other products to try, based on looking at where else people have tried to remove lime and scale. All of these have the same precautions as muriatic.

Photo at left: lime scale fragments collected from a water heater. [Click to enlarge any image]

Take a look at some boiler cleaning chemicals (and their ingredients) Noting that some of the info sources I give below want to sell only ridiculously huge quantities, we're interested in what's in them, (the MSDS info sheets often is enough) and trying a couple of representative samples.

These will be available in smaller quantities from a local heating supplier (normally) but for fellow like you who don't work in an area with lots of hot water heating systems you may have to order online.

 "Limescale" I'd test small quantities of liquid and foam boiler scale cleaning chemicals. Keep testing to small quantities and small areas for the litany of reasons we've discussed. As lime scale deposits are sometimes reddish, there are also rust-removing cleaners but I am doubtful that it's similar chemistry and so probably less useful.

You can see in Wikipedia's limescale photograph that we're dealing with a hardened calcium/magnesium deposit material, but it is somewhat porous and may be attacked and dissolved by very soft water or more aggressively by cleaners, usually acids. We've found that for hardened lime deposits a mild approach such as a vinegar poultice is slow and thus not effective for your situation.

Photo at left: Limescale deposits, SEM scanning electron microscopy micro-graph with a field of view of just 64 x 90 microns. Source: "Limescale" - Wikipedia, retrieved 11/13/2013

Take a look at these lime removers and de-scaling products

Other supply sources for de-scalers given that vinegar and similar mild approaches are not working. Lime scale is principally calcium carbonate, possibly also containing magnesium, and sometimes stained reddish from iron content. Wikipedia has some scattered but useful details: typically acids are used to remove or soften scale. That's why we've been discussing such products. Some sources refer to lime scale or mineral removal using chelation. A commonly used synthetic chelator is ethylenediaminetetraacetic acid.

Finally, also from Wiki, we might later look at lime water softening - but I am very doubtful that it is quick enough to work as a roof cleaning procedure. I quote below (but you can ignore)

Softening can be achieved by adding lime in the form of limewater, Ca(OH)2, which, in a carbonatation reaction with CO2, forms calcium carbonate precipitate, reacts next with multivalent cations to remove carbonate hardness, then reacts with anions to replace the non-carbonate hardness due to multivalent cations with non-carbonate hardness due to calcium. The process requires recarbonation through the addition of carbon dioxide to lower the pH which is raised during the initial softening process.

As lime is added to raw water, the pH is raised and the equilibrium of carbonate species in the water is shifted. Dissolved carbon dioxide (CO2) is changed into bicarbonate (HCO3-) and then carbonate (CO32-). This action causes calcium carbonate to precipitate due to exceeding the solubility product. Additionally, magnesium can be precipitated as magnesium hydroxide in a double displacement reaction.

The process is interesting in that both the calcium (and to an extent magnesium) in the raw water as well as the calcium added with the lime are both precipitated. This is in contrast to ion exchange softening where sodium is exchanged for calcium and magnesium ions. In lime softening, there is a substantial reduction in total dissolved solids (TDS). In ion exchange softening (sometimes referred to as zeolite softening), there is no significant change in the level of TDS.

Lime softening can also be used to remove iron, manganese, radium and arsenic from water. - Wikipedia, Lime Softening, retrieved 11/13

Reader update:

I contacted Graingers and they recommended a product called "Calcium and Lime Remover," item # 4tmk3. This product contains phosphoric acid; not sure if it's compatible with asphalt? do you suggest I give it a try? The spokesperson I talked with said sulfuric acid may be the way to go? Also sent an email to the folks in Texas and requested information on the sublimedescaler product and a demo kit. I am also going to research boiler cleaning chemicals and distributors. Again, I am convinced there is a solution out there; it just feels like finding snow in the summer in Albuquerque may be easier!


I'd try the HCL or phosphoric acids first. The various products I reviewed with that acid claimed those were safer to work with. Sulphuric acid is really dangerous in concentration. I learned as a kid to repeat

Johnny was a good boy, but Johnny is no more, for what he thought was H2O  was H2SO4.

References for Cause & Cure of White Calcium or Mineral Stains on Roofs

White Stains on Wood Shingle Roofs

Moss on a wood shingle roof (C) Daniel Friedman

The "white stains" shown on this wood shingle roof are in fact not a stain but an absence of lichens or moss.

Metal salts washing down the roof surface from metal chimney flashing are often enough to kill of biological organisms that otherwise stain various roof surfaces: algae, lichens, and moss for example.

The photo at left is an example of roof moss prevention discussed at MOSS on ROOFS. There we commented:

We have observed that the chemical or mineral salt wash-off from some building materials like aluminum flashing and copper flashing and even some paints which appear to kill of moss, lichens, algae, and fungus, as their extracts are washed over the roof surface. It's particularly easy to spot this effect by noticing where there are moss-free areas on an otherwise mossy roof surface.

One of our most obvious photos of rain wash off of copper flashing keeping moss off of a roof happens to be on a wood shingle roof, But we see this effect below copper flashing (and often aluminum flashing) on asphalt shingle roofs as well.

There may be cases of wood shingles absorbing water that then evaporates to leave a white stain, but since ulike stone, slate or tile roofing wood shingles don't naturally contain high levels of calcium or magnesium that might be accumlulated on the shingle surface as a white lime deposit, I think that hypothesis is speculative.


White Stains on Stone Roofs

Stone roof, Molde Norway (C) Daniel Friedman Lichens on stone mistaken for white stain (C) Daniel Friedman

The stone roof at above left (Molde, Norway) has some normal light-colored areas that I do not think are a concern. The white or light gray "stains" on the stone wall at above right can also appear on stone or slate or other roof materials. Lichens is not a stain in the proper sense of the word, but on asphalt, wood, or some other surfaces it can damage the roof and reduce its future life.

Worse, aggressive cleaning of lichens from a roof surface is likely to ruin asphalt roofing and other softer roof coverings.

Also see:

White Stains on Slate Roofs May Indicate Roof Age

White stains on slate roof - age sign (C) Daniel Friedman

White stains formed on roofing slates such as in the roof pictured here are almost always a white mineral salt deposit or effloresence left by the evaporation of water that was absorbed into and that dissolved salts within the roofing slage.

White stains forming on slate roofs (photo above) are interpreted by many slate roofers as an indication of remaining roof life.

As the stained area increases from the perimeter or periphery of the roofing slate towards its center, slate roofers reason that more of the slate area is absorbing water or becoming softer or more porous.

In our experience there is some basis for this view, but because the chemistry and hardness of roofing slates varies significantly from quarry to quarry we are not sure that one can make a quantitative rule about white slate roof stains and remaining life.

Also see:

PAINT on STUCCO, FAILURES also describes white blotches showing up on building surfaces because of improper painting or sealing of masonry or stucco materials. Our Efflorescence article above also diagnoses white stains on chimneys.

White Stains on Tile Roofs Indicate Water Absorption

White stain diagnosis on a clay roof tile in Mexico (C) Daniel FriedmanAs with the slate roofs discussed above, white stains on tile roofs are typically an efflorescence deposit and may indicate that the tile is absorbing water, thus nearing end of life.

However where we have seen white effloresence staining on clay tile roofs (such as the Mexican clay tile roof photographed below) I have not seen a notable correlation with remaining clay tile roof life.

The amount of water absorption into clay roofing tiles depends on the extent of clay vitrification, in turn an effect of how the clay tiles were fired or produced.

Soft low-vitrification clay tiles such as those shown at above left (Mexico) are more likely to absorb water and would not perform well in freezing climates.

Generally low-vitrified soft clay tile roofs fail due to the fragility of the roofing tiles themselves, not from water absorption and mineral salt formation.

Details about white stains on clay tile roofs are at CLAY TILE ROOF DAMAGE & WEAR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see STAIN DIAGNOSIS on ROOFS for a complete catalog of roof stain sources & causes


Continue reading at EFFLORESCENCE SALTS & WHITE DEPOSITS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see STAIN DIAGNOSIS on ROOFS for a complete catalog of roof stain sources & causes

Suggested citation for this web page

WHITE STAINS on ROOFS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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