Fair Go puts deck cleaners to the test

Spring is here and cleaning your deck is more than just a vanity project.

ACC has revealed to Fair Go that in 2021, it was managing 10,823 active claims for slips on decks at a cost of $21.7 million.

This year is on track to be just as costly and harmful.

ACC stats also show that most who slip suffer soft tissues injuries but last year 144 were left with a concussion or other brain injury.

No question then, we should get those winter decks safely cleaned - but what Fair Go found was a bewildering range of options at the hardware stores for cleaning mould and grime from a timber deck.

And many products claimed to do the job - despite using very different active ingredients. Such as?

"Sodium hypochlorite, which is standard household bleach, as in Janola. Oxalic acid is in one of the products. The strong acid is not good for cells so that has an effect on the mould. There's also sodium percarbonate which is also an oxygen-based bleach," says Associate Professor Joanne Harvey from Victoria University's School of Chemical & Physical Sciences.

"Bleaches are not good for living cells and so they are good at inhibiting the growth and to some extent killing the mould that might be on your deck. Also, what they're particularly good at is decolourising."

Meaning they're making the mould less visible, but does it clean it away? Harvey says there's a little controversy in the science literature about that.

"All of those active ingredients will have a role in killing the fungus cells so it's just a matter of whether you can kill them all, likelihood is not in a highly porous material like wood, which is why you have to keep repeating the application, " says Harvey.

She adds that annual cleaning may be enough in some places, where others will need it every six months to kill off recurring mould fungus.

Those cleaning products also require compounds that lift and spread the mould and grime by making it stick to and disperse through water - they're what's called a surfactant.

"It gets attracted to charged dirt particles and the greasy end gets attracted to greasy slimy bits on your deck."

Armed with that knowledge and a couple of online recommendations for homebrew recipes, Fair Go went shopping, and purchased three popular products.

Our two homebrews were simple.

Carefully following the maker's instructions, we applied all five to sections of a mouldy, grimy section of wood.

Shown the results, our expert Joanne Harvey and all of the manufacturers agreed - good results all round - including for the homebrewed recipes.

The cost of those is hard to estimate; we don't know how much coverage we'd get from a bottle of bleach at $2.12 per litre or from the oxy-bleach powder at $14.90/kg.

As for the big brands based on what they claim they can cover, Cabot's $22.48 for 1 litre works out at $2.25 a square metre, though buying bigger quantities would be cheaper.

Hit the Deck says depending on how dirty the deck, its $68 1.7kg tub would clean 60-90 square metres and cost between 76 cents and $1.13 per square metre.

30 Seconds claims its $36.98 2 litre pre-mix would clean 83 square metres of deck, which works out to just 44 cents per square metre.

However, Fair Go did want to know why 30 Seconds offers four different products that all have the same active ingredient - do shoppers need to purchase its Outdoor Cleaner, Mould Off, Deck and Driveway Cleaner and the House Cleaner when just one would do?

30 Seconds says the four use the same ingredient but mixed to different concentrations for the different jobs.

Shoppers could instead buy a concentrate and mix it for the job if they don't want to pay extra for convenience, but that convenience seems to be the brand's strong selling point.

"There’s no need to handle chemicals – all you need to do is connect the garden hose to the bottle," says the 30 Seconds team in a statement.

Cabots uses oxalic acid and its manufacturer warns: "Bleach whitens the timber and strong concentrations of sodium hypochlorite can damage the timber substrate."

Wet & Forget says it's milder than either of those rivals: "We wanted a product that didn’t burn us, that didn’t bleach our clothes and which didn’t kill the prize petunias or the cat," as company founder and managing director Rod Jenden puts it.

"Hit The Deck has a pH10, which is extremely mild, compared to (chlorine) bleach-based deck cleaners which have a pH12.3 and are fierce oxidising agents, and of course, very aggressive to skin, fabrics, wood, and metal.

Other products use Oxalic acid which have a pH1 which is extremely acidic."

Jenden also urges the use of its proprietary brush which Fair Go also tested - at $25 it might be well worth the money.

As powerful as the chemistry is, you need to add some physics too - a good scrubbing motion.

"You just want a product that will do your job for you but to be honest you will get the best lasting results if you use elbow grease as well as chemical agents," says Associate Professor Harvey.

Whatever you use, Harvey says you should add PPE: gloves, footwear, eye protection and plenty of ventilation, so mix anything outdoors if possible.

Here's one last but very important point. Mixing anything with bleach needs care. Read the label. Never add anything to bleach that contains ammonia; that can make a dangerous gas instead of a cleaner deck.