Fragile Earth

How Patio Cleaners Work

Fragile Earth Path Patio decking and hard surface algaecide

For a long time, many of us didn’t question the need for chemicals in our cleaning products they seemed like the only option to ensure effective cleaning and good hygiene. For indoor domestic use, eco-friendly products have become ever more popular when you think about it it does seem contradictory to be using hazardous ingredients to try to make our homes safer, but for outdoor jobs, we still have a way to go.

The use of toxic chemicals to clean outdoor surfaces has become normalised, so many of the products which we commonly use contain incredibly harsh chemicals which are dangerous if ingested, touched or even breathed in. But because they are used outdoors and not contained within the confines of a room we somehow expect any adverse effect to be mitigated or diluted by the environment, remember ‘there is NO away, it all has to go somewhere.

Many of the chemicals used in outdoor cleaning products are not only potentially dangerous to us but to our pets, wildlife, soil and plants and can end up in our waterways, becoming extremely damaging to the environment.

Patios and decking have become an extension of our indoor living space providing areas for relaxation and entertaining, like indoor spaces we want to keep them clean and attractive. Over time the build-up of organic (living) matter such as mould, algae, moss, fungi or lichen plus debris such as rotting leaves and soil from foot traffic will need to be removed, so we reach for a patio cleaner, but be aware they may not be as effective or friendly as you might think.

Most patio cleaners contain chemicals that will kill living organisms. They can be described generically as biocides or more specifically as algaecides, fungicides, or sometimes, herbicides or weed killers. Some also contain detergents to help clean, salts as a herbicide and acids some naturally occurring such as acetic acid (organic), and some inorganic such as hydrochloric acid to perform the same biocidal function.

One important thing to note, products that act as biocides (kill living organisms) do not remove them as well, there’s truth in the saying that ‘dead weeds look worse than living ones’, often a good reason not to use herbicides, the thinking goes that if you have to pull out dead weeds by hand (or scrape/brush off) you might as well pull out living ones and save the cost and negative impact of using a chemical.

This is also true of moulds, moss, lichen, fungi and algae once killed they do not magically vanish they remain, albeit dead, until they are dislodged, blown or washed away. Much of the sales pitch for patio cleaners plays on our desire for a ‘work-free’ solution promising sparkling results returning the surface to ‘just like new’  these claims are almost always exaggerated. Statements like ‘no scrub’ and ‘no pressure washing’ are very appealing to our more indolent tendencies, but the contamination they kill will still require the action of gravity, weather or you to do the mechanical removal.

Patio products also often claim instant cleaning which has a big appeal, however, the way most biocides work requires the target organism to be active to allow the ingredients to work, this means that in colder temperatures the action will be slower and the full effect may take several days or even weeks to become evident. On the plus side, the product should work given enough time, many proprietary products will also provide some longer-term protection against regrowth which means that it is normally sensible to apply more frequently than a once a year blitz so reducing the overall level of contamination in the long run.

Also, it’s worth considering the type of organism you are trying to remove, algae and fungi and most mosses require damp to thrive, lichens can tolerate much dryer conditions this also has an impact on the time it takes a product to work. There are some products that can work very fast but these tend to be highly aggressive and require protection for the applicator and surroundings during use, products such as brick acid would be an example – see note below. Generally, if you are enjoying the clement weather then so are the organisms growing on the patio. Warmer, dryer, sunnier weather will allow faster results, darker, colder, wetter weather will mean slower results.

Cleaning living organisms off surfaces with the aid of a biocide is a good idea it makes cleaning quicker, easier and more effective and will offer some residual action.  Pretty much all commercially available cleaners will work, where they don’t it will be down to applicator error (for example the wrong dilution), timing, for example, too soon before rain arrives or if it is either too hot or too cold. In almost every situation the combination of some physical action coupled with a cleaner (biocide) and time is the best way to clean the surface.


The ingredients in most commercially available cleaners are synthesised chemicals, many are diluted for sale as the more concentrated versions are toxic and require special labelling and handling. Unfortunately, many of the ingredients used in patio cleaners are not biodegradable, or they have other negative health effects. They can also harm the soil, plants, animals and aquatic life.

You may end up with a clean patio but consequential damage is also a possibility, pets and wildlife may be endangered, neighbouring plants can be killed or damaged, grass may yellow, aquatic life can be threatened and, importantly, soil organisms can be seriously damaged including by ingredients that can appear harmless like common salt. QUATS and BACS are also salts – see below.

One other often seen claim is that the product is ‘non-toxic when dry’, this does beg the question about use in the winter months when surfaces can remain damp or wet for weeks. Products that are genuinely non-toxic will be benign in all circumstances even when wet.

Good advice is to look out for the following warnings on the label, any of these can indicate the inclusion of aggressive and potentially harmful ingredients.

  • Harmful to the environment
  • Harmful if swallowed
  • Do NOT induce  vomiting
  • Harmful in contact with skin
  • Causes serious eye damage
  • Causes skin irritation
  • Very toxic to aquatic life with long-lasting effects
  • If swallowed call a poison centre
  • Non-toxic safe for use around children & pets when dry
  • Wear protective clothing
  • Do not dispose of down the drain


Look out for these warning symbols they indicate adverse effects of the ingredients.

  Irritant             Corrosive              Harmful to the environment     Oxidising Agent     
Irritant Corrosive Harmful to the Environment Oxidising Agent




We come clean about what’s in ours….

Fragile Earth Path/Patio/Paver & Decking cleaning products contain 100% plant-derived active ingredients. In our formulations, we use different blends of our own unique Certified PSLog6 biocide which kills 99.9998% bacteria, yeast, fungi, viruses and protozoa and biologically fermented acetic acid (non-chemical) which kills moss, algae, lichens and green growth. We add just enough of our active ingredients to be effective whilst helping reduce waste and cost. In all our biocidal/algaecidal products the formulation acts quickly, within 30 minutes, is fully biodegradable, non-toxic and certified as safe under the Biocidal Products Regulations (BPR) EU528/2012 PT1, 2, 3 & 4. Our products do not require hazard warning labels as they don’t contain any harsh or damaging chemicals, they act quickly and have proven levels of efficacy in a wide range of applications including medical, livestock, food processing, catering, hospitality, horticultural, equine, domestic, commercial and industrial.


If you want to avoid any potentially harmful effects then don’t use products that contain these ingredients.

Sodium Hypochlorite

Sodium hypochlorite is most often encountered as a pale greenish-yellow dilute solution commonly known as liquid bleach or simply bleach, a household chemical widely used (since the 18th century) as a disinfectant or a bleaching agent. The compound in solution is unstable and easily decomposes, liberating chlorine, which is the active principle of such products. Indeed, sodium hypochlorite is the oldest and still most important chlorine-based bleach.

Sodium hypochlorite, in its pure form, is a water-soluble, yellowish liquid that contains about 12% chlorine and is an extremely powerful oxidizing agent. It will corrode or destroy most metals, react with acids, peroxides, and many other chemicals to produce toxic chlorine gas. Bleach will dissolve paper, cloth, and many other organic materials. Even in the 5% household strength, bleach is still a potent oxidizer and disinfectant with very high alkalinity. Caution must be used when working with bleach. Even in diluted form, the fumes can produce severe irritation to the respiratory system. Skin contact can result in mild irritation to burns. Prolonged eye contact can cause permanent damage. Bleach contains NO cleaning agents.

Quaternary ammonium compounds (QUATS)

Quaternary ammonium compounds are a highly persistent disinfectant predominantly used to offer antibacterial action they can display a range of health effects, amongst which are mild skin and respiratory irritation up to severe caustic burns on skin and gastrointestinal lining (depending on concentration), gastrointestinal symptoms (e.g., nausea and vomiting), coma, convulsions, hypotension and death.

Products that contain QUATs can also be described as acid and bleach-free, biodegradable and non-caustic.

Benzalkonium chloride (BAC’s)

Also known as BZK, BKC, BAC, alkyldimethylbenzylammonium chloride and ADBAC, is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. BACs are the most common ingredient in patio cleaners as an algaecide for clearing of algae, moss, lichens from paths, roof tiles, swimming pools, masonry, etc. BACs are active against bacteria and some viruses, fungi, and protozoa. Bacterial spores are considered to be resistant. Activity is not greatly affected by pH but increases substantially at higher temperatures and prolonged exposure times.

Benzalkonium chloride is a human skin and severe eye irritant. It is a suspected respiratory toxicant, immune-toxicant, gastrointestinal toxicant and neuro-toxicant. BAC’s can be absorbed into the body through the skin and by ingestion. Decomposes on heating this produces toxic and corrosive fumes including ammonia, chlorine and nitrogen oxides.

BAC formulations for consumer use are dilute solutions. Concentrated solutions are toxic to humans, causing corrosion/irritation to the skin and mucosa, and death if taken internally in sufficient volumes. 0.1% is the maximum concentration of benzalkonium chloride that does not produce primary irritation on intact skin or act as a sensitizer.

BAC is very toxic to aquatic life. It is toxic to cats and dogs and can remain active for a long time, this is why products containing BACS say non-toxic when dry as in a soluble state they remain active. BAC’s are irritants and can cause adverse effects in cats that have licked or walked over treated surfaces and then groomed or cleaned their paws and ingested the chemical. Similar effects can occur in dogs.

Fragile Earth pet friendly patio cleaner

Products that contain BACs can also be described as acid and bleach-free, non-caustic and biodegradable however their resistance to microbial biodegradation can cause accumulation in aquatic environments, where toxicity to aquatic organisms can occur

Tetrasodium Ethylene Diamine Tetraacetate (EDTA)

EDTA is the salt resulting from the neutralization of ethylenediaminetetraacetic acid It is an amino polycarboxylic acid a colourless, water-soluble solid. It is widely used to dissolve limescale. Its usefulness arises because of its ability to sequester metal ions such as Ca2+ and Fe3+ it is also used to stop the growth of mould and other microorganisms.

EDTA can cause abdominal cramps, nausea, vomiting, diarrhoea, headache, low blood pressure, skin problems, and fever. Too much can cause kidney damage, dangerously low calcium levels, and death.

Interest in environmental safety has brought up concerns about biodegradability in EDTA it is in such widespread use that questions have been raised whether it is a persistent organic pollutant. While EDTA serves many positive functions in different industrial, pharmaceutical and other applications, the longevity of EDTA can pose serious issues in the environment. The degradation of EDTA is slow. It mainly occurs abiotically in the presence of sunlight.

Hydrochloric acid (includes muriatic acid HCI) 

Sometimes called brick acid be careful that the acid doesn’t come into contact with clothing, skin and eyes.  The fumes can be very toxic too, potentially causing damage to the nose, throat and lungs.  Children, pets, plants and grass should be kept away as it will damage or kill just about anything organic.

Concentrated hydrochloric acid (fuming hydrochloric acid) forms acidic mists. Both the mist and the solution have a corrosive effect on human tissue, with the potential to damage respiratory organs, eyes, skin, and intestines irreversibly.

Acid cleaners can damage metal, limestone, concrete, lime containing (cement) masonry composites, jointing mortar and other porous materials, use with extreme care.

Diethylenetriamine (abbreviated DETA and also known as 2,2’-Iminodi(ethylamine)

Added as a wood perseverative to decking cleaners. Dipropylene triamine is very toxic by inhalation and toxic in contact with skin. Harmful if swallowed and it can cause burns. May cause sensitization by skin contact.

Sodium metasilicate (include inorganic sodium salts)

Sodium salts are not inherently unsafe but will damage plants and are toxic to many soil organisms.


The most commonly used ingredients in Patio Cleaners are QUATs including BACs and Sodium salts.



This information was assembled from a wide variety of sources and no warranty, expressed or implied, relating to the accuracy of the information is made. The user assumes all liability for any damage or injury resulting from the use or misuse of this information