Outdoor Cleaning Products

Choice has been big on providing comparison testing on everyday household products.

Would it be possible to also look at outdoor cleaning products/chemicals.

Three things stand out.

  1. How well does the product perform?
  2. Is it value for money?
  3. Is it safe, to you, your house and the environment?
  4. How complete and effective or reliable are the instructions for safe use?
    (That’s four now!)

Typically you are trying to do more than just lift off dirt and dust. Algae, mould, moss and lichen are also the enemy.

Some products appear to have similar ingredients, but the price differences are significant, just on brand identification? Roof cleaner concentrate $99 for 5l on line vs $39 for a competitor at Bunnings. See below for links.

The other consideration is that these products are typically used on larger home cleaning jobs, hence they are not $2.00 projects.


It’s also possible to be left with an impression that some of the active ingredients carry risks that are not well communicated. Eg A user instruction to not spray if rain is likely might be good advice.

Would it be better to have also said avoid run off onto lawns, gardens and waterways for xyz days? This assumes the active ingredient can be harmful to aquatic life and invertebrates, which some can be. You don’t usually need to consider these types of risks for cleaning products used inside the home.


The active ingredients for Wet&Go and 30 Seconds are different…they are outlined in the MSDS for both products:


30 Seconds:

The active ingredients for both products contain compounds which are highly detrimental to aquatic biota and applying these chemicals to outdoor surfaces exposed to the weather increases its risk of being washed into local waterways.

The concern is that the average punter possibly won’t understand the ramifications on not using the product wisely and misuse can potentially cause significant offsite environmental impacts (especially when applied and the compounds when active are allowed to wash from the treated area to stormwater and ultimately waterways).

Many of the things that these compounds treat are potentially not an issue if left untreated. This includes things like lichen on ones roof, moss or moulds on external concrete surfaces etc. These are more cosmetic rather than being a long term damage to the structure covered by these ‘things’.

The other impact could be using these products on roofs which also have rainwater tank systems. The consumption of these chemical compounds due to the chemicals being washed into a rainwater tank may not be wise.

I can see the need for such products where say a walking surface has a high cover of mould/algae and become slippery when wet. However, there are possibly cheaper and just as effective treatments for the mould/algae removal such as a high pressure cleaner, using boiling water/heat gun or even old fashion scrubbing and rinsing.


I did the pressure wash on my driveway twice per year for a decade and it continued to get mildewed again because it is shaded and often damp. The Wet & Forget brushed on the concrete worked a treat and had no visible detrimental affect on the surrounding plant life.

For most things there is a trade off. There are usually alternatives to most anything, but alternatives are not always practical for one or another reason. Re a driveway, one (esp a senior) can only do so much ‘scrubbing and rinsing’ or boiling sufficient water for a fairly long drive, and then waiting to see if the mildew comes back, if that makes a point. As for heat, I did not investigate serious models.



Used to get moss on a concrete pathway which got little sunlight, at the house I was living in. Neat white vinegar, left on for at least a few hours, would kill the spores off and a scrub and rinse off was all that was needed (until the next winter).
Unlike bleach, vinegar penetrates porous surfaces like concrete, and it is not a dangerous substance.
The Home Brand cleaning vinegar is not expensive and easily found at most supermarkets.


Thanks for the request @mark_m, will be sure to pass this onto our product testers :+1:


I’m all for the easy way, and use a number of similar products for prepping the timber before repainting. It takes more than just a mould inhibitor in the paint around here.

If you don’t kill the root of the mould spores it just keeps coming back. I do like the thought of using the direct flaming technique noted by @PhilT previously. It just might not be that great for the house!

It may help looking further down the 30 Seconds product list. As well as the general outdoor cleaner which uses sodium hyper chlorite, there is a specialty Concentrated Roof Cleaner/treatment product.


MSDS found at:

It contains a quaternary ammonium compound, as does the Wet and Forget Roof Treatment!

For more general cleaning products EG 30 Seconds outdoor cleaner, there is a different chemistry as you have noted.

Many of the outdoor cleaners rely on the action of chlorine to do the neutralising of the mould, moss etc. The delivery mechanism is all that varies.

Somebody more knowledgeable might like to explain where all the chlorine in these products ends up, for better or for worse?


I assume you mean the hypochlorate as found in many bleach solutions then the majority of it ends up as salts, such as sodium chloride, sodium carbonate & Chlorine (Cl2) as it reacts with CO2 in the air, potassium chloride, chloramines and related compounds (the smelly stuff in pool water from reactions with nitrogen compounds), chlorine gas (resulting from reaction with acids where the hydrogen atom bounds with the OH chain creating water and releasing the Cl as Cl2).

As the gas is very reactive it usually ends up then bonding with sodium, potassium or similar metals to form salts as an end product. It also forms other compounds such as chloroform, carbon tetrachloride, and organochlorides but usually at “safe for exposure” levels.


Yes please add these outdoor cleaning products to the CHOICE comparison test. I’m quite keen to see results especially on all those 30 second products considering how dominant they are in Bunnings.


I found this (old!) thread after researching moss-removal over the weekend. We have a large area of flagstones that gets lots of sun, but is seriously moss-impacted (lots of silt washed down from the garden, then moss, then mess). I’ve peeled off a large amount of moss, but eventually it’s going to need blasting or killing. And there is lots of moss patches infiltrating shady parts of the flat buffalo grass bed higher up. Actually, the moss is getting more brazen.

And here’s the challenge: there are a number of products on the market; they all profess to be easy and instant; they are universally expensive AND in quantities larger than I need; but the killer (and not of the moss): zero consensus on how well the products work.

For instance: comments on “ProductReview” where opinion is strongly divided. Some users had great experience, some had zero luck, but there’s no thread to indicate why such a disparate range of experience.

This is exactly the sort of information (and scientific input) I look for from Choice.

Summary: It’s very hit and moss. Not something I’m lichen. A mold I’d like to break. Could Choice provide some advice, and possibly stage a longer-term test process - as you did with paint?


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I can’t help you with specific recommendations as I don’t have the problem and have never needed to kill moss.

As for the holy grail of cheap, effective, harmless, long lasting and effort free, I doubt you are going to get all that in one bottle. The problem is that whatever the active ingredient is it will not stay there to kill moss forever. If you have areas that are cool and damp moss will keep growing back once whatever inhibits it is gone. Even if it works well for a while you may be better off buying larger quantities as you are likely to have to re-apply it. I would look at other solutions first.

You say the area gets plenty of sun. Generally moss doesn’t like full sun, are you sure what is growing there is moss? Could you post a picture? It is common for people to lump moss, algae, mould and lichen in together but they are not the same.

Other than more sun the other thing that reduces moss is less water. It may be practical to improve the drainage to the area and that could be a permanent fix. The other thing that may help is once you get it clean to keep it that way by regularly sweeping off dust and mud while it is loose before any growth can get established. You don’t want to do any of that? Well you may be out of luck.

You say that silt washed down is part of the problem. That is where I would attack it first. Moss is a green plant that needs minerals and moisture which are held by the silt. Consider a drain that runs across the upper edge of the flagstones that runs into a sump that you can dig out. Alternatively look at stabilising the garden area, both the soil and the drainage, so that runoff doesn’t cross it on the way to the flagstones.


Hi Syncretic

So thank you for bravely wading in. :+1:

I’m a technology project person by day, so I fully agree that a cheap/good/quick solution most likely isn’t. Conventional wisdom says “pick any two”, but it’s not impossible to have all three. And since there are consumer products on the market claiming those attributes, it’s a good topic for Choice to review.

Re your other points: agreed that there seem to be many contraindications and anomalies. I don’t know why a sunny area attracts moss (I have theories), or why the grass has moss (I have more obvious theories), or why there’s so much silt (I blame brush turkeys for denuding the stuff that retained the silt). Yes to sweeping.

This project is the big clean up after a period of minor neglect, and right now I don’t have the ability or resources to fully attack the cause. I’m definitely not a competent gardener by nature, so some sort of treatment is needed while investigating a longer term solution - assuming there is one, and there might not be without doing something unnatural.

Here’s a collage of the mossy masses:

I’m pretty sure that it’s moss, but I’m not the expert. Bottom left is unwanted green stuff showing through what should be lawn. Other shots are a different form of green stuff firmly attached to various forms of paving or boulders. Some of that area is VERY exposed and sunny when there’s sun, and it’s already dry right now after a weekend of rain. There is lichen on some other boulders, but not very much.

Bottom line is that I need to play the cards that have been dealt, and the moss is just asking for a flush.


Yes it is moss.

Moss will grow in full sunlight if the conditions are favourable…usually moist, protected areas.

Moss is easy to remove from hard surfaces. Use either a stiff brush or spade to remove the bulk of it and then use strong hose/high pressure cleaner to remove anything that remains.

Regular sweeping and keeping surface clean should prevent it coming back.

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Moss also prefers acid soil conditions. The spores are prolific. The soil that is washing down may be carrying spores, however where the moss has been growing there will also be a build up of spores in the ground.

Stabilising the soil that is washing down and adding to the problem has been suggested. There are a number of products available from landscaping and hardware stores that use an open plastic mesh, or natural materials. These will also restrict or deter the turkeys activities.

Adding lime to soil raises the pH. Depending on how the area is set out it may also help. Removing the build up and moss, cleaning the paving with a pressure cleaner and improving the drainage (as suggested by others) are how we managed moss and algae growth around paved areas at a previous property.

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Thanks @phb and @mark_m for the suggestions, and for your comments on moss generally. Most useful.

I thought about pressure blasting the courtyard, but my fear is that this will force moss fragments into garden beds, and thus propagate the moss further in the one place I definitely don’t want it. Would that be correct?

By the way, while I appreciate the focus on green ways of managing green, this isn’t answering my fundamental question about the efficacy of products marketed to address the problem.


Do so once you have scraped up all the extra dirt and growing moss.

There are various chemical treatments. Changing the conditions and removing the sources of the moss spores is treating the cause. Applying chemicals to the courtyard is only treating the symptoms. That’s from personal experience using a variety of branded outdoor cleaners.

There are various treatments including professionally registered schedule 6 chemical products (poisons). Chemical treatments may not be a permanent solution. They may not be appropriate for your particular needs.

If the enquiry is concerning moss control in general and the types of products available it may be useful to request a test in the following Category.

We do have moss growing in several small sections of our lawn. It appears when it has been very wet and winter shade becomes more the norm. It dies back in spring with dry weather and spring sunshine. I scrape up any large patches where they are a problem and bin or add to the compost. Yard maintenance, comes with having a yard to enjoy.


Jumping back in. I let this lie for a bit while I contemplated the yard and my navel. After doing a lot more manual cleanup, I decided I definitely needed to try multiple solutions.

This year we have more moss and crappy weeds than I’ve ever seen in this patch of grass, and I decided it’s time to go to war. Last week I purchased a bag of “Manutec moss killer and lawn food”, claimed to feed buffalo and be unfriendly to moss. It was distributed over the area a few days ago, and yesterday/today it’s being watered-in thanks to a solid amount of rain. According to the pack I should see appropriate changes to the wanted and unwanted components of the lawn area over the next week.

Fully agree. After contemplation, I concluded that I’m sadly limited in my ability to change conditions or remove sources, but also wringing my hands didn’t seem to be a good response either. So also over the weekend I sprayed most of the mossy and lichen surfaces with “30 second spray and walk away”, which is benzalkonium chloride, mixed at the stronger recommended strength. The moss (which had dried out somewhat after many dry sunny days and should have been thirsty) then had 24 hours of further drying time followed by a Sydney deluge acting as a thorough wash. Timing seems to have been perfect.

I had low expectations of visible change but, ahead of the rain, areas of moss that had been fluorescent green were looking very ordinary and possibly even yellowish. The moss also seemed to be releasing from the stones more easily than it had. Today I’m seeing patches of yellow and black, and that’s after a heap of rain. Who knows? Maybe the claims aren’t bogus!

Yep, that’s going to be my next step. This is definitely a topic for which some science and investigation would be welcome.

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