Cleaning Timber Decks and Fences

How To Clean Decks, Fences and Cladding with Bio-Shield®

Including cleaning of:

• Hardwood Decks

• Softwood Decks

• Composite Decks

• Timber Fences

• Cedar Cladding

Should I water blast clean or use Bio-Shield® to clean timber?

Water blasting timber to remove moss, algae and lichen growths can damage the surface. The pressure required to remove moss, algae and lichen will damage the timber fibers leaving deep gouges and a furry striped finish.

The best method for cleaning timber is to use a mild, bleach free exterior cleaner like Bio-Shield.

Treating a deck with Bio-Shield will kill and gently remove the growths over time then keep the surface clean for extended periods. 
Regular applications of Bio-Shield at the first sign of re-growths will effect a rapid clean up and keep the surface clean again for an extended period.
A deck that is kept clean with Bio-Shield® will also prevent the build up of black algae and lichen growths that make a deck slippery and dangerous to walk on when its wet.

Why choose Bio-Shield® for your D.I.Y Deck Cleaning?

Bio-Shield has been developed through 39 years of use in a demanding commercial environment so it works extremely well.
Bio-Shield is a high quality product, and contains no bleach, salts, acids or phosphates.
The high concentration of active ingredients in Bio-Shield® when compared to other outdoor cleaners means it will cost less per diluted litre and cover more area at a lower cost.

Hardwood Timber Deck with Lichen, Black and Green Algae
Hardwood Timber Deck with Lichen, Black and Green Algae
Hardwood Timber Deck - Cleaned with Bio-Shield

 Bio-Shield® Application Instructions


For a successful DIY job, preparation is the key. Following these simple steps will ensure a professional looking finish and long lasting protection against moss, algae and lichen damaging your timber deck.

Remove pets toys and feeding bowls from the area to be treated.
Keep children and pets off the treated surface until it dries.
Do not feed pets on the treated surface until  the surface has been flushed by rain.
Remove loose debris, tree leaves, dirt etc, from the deck.
Cutting back overhanging trees will help the deck to clean up and help keep it clean.
The timber surface should be dry or damp to maximise absorption of the Bio-Shield solution.

Check the weather forecast, or rain radar - ideally no rain to 3 to 4 hours is the minimum requirement for treating timber.
Air temperature above 10 degrees C° will help to accelerate biocidal action.

Premix the Bio-Shield® 1 part to 20  parts water in the pressure sprayer.
For heavily blackened decks or decks with trees nearby, use the stronger 1:15 mix = to 65ml - 1000ml water

Bio-Shield Mixing Ratios - for Pressure Sprayers

Clean WaterBio-Shield ConcentrateDiluted Bio-Shield
1 Litre50 or 65 ml1.05 or 1.065 L
10 Litres500 or 650 ml10.05 or 10.65 L
15 Litres750 or 975 ml15.75 or 15.98 L
20 Litres1.0 or 1.3 Litre21 or 22.3 L

CAUTION - Bio-Shield is OK to use on cedar and other timber house walls and windows. If the surface is not exposed to rain e.g. under the eaves or high on the wall, it will need to be washed down to assist removal of the Bio-Shield and dead growths. Care should be taken when using Bio-Shield around old powder coated aluminum window frames, where the powder coating is oxidised. Most types of outdoor cleaners will leave marks on the darker colours that have oxidised (aged). 

Application is best done on an overcast day at any time of the year, or early morning once the deck has dried or in late afternoon in summer if a warm sunny day is forecast. This slows evaporation and speeds the treatment process.
Application on a damp deck is OK as long as the deck fully dries after the Bio-Shield has been applied.

Fill your sprayer with the premixed Bio-Shield solution and pump it up to pressure.
If using the Jet-Stream Applicator, follow the set-up instructions on the bottle label or watch the instructional video.
Timber decks must be thoroughly saturated and this will take 2 to 3 consecutive coats to achieve and keep the timber wet for the 10 to 15 minutes required for the Bio-Shield to kill.
Apply in slow even strokes allowing the following stroke to overlap the previous stroke by 50% to ensure even and complete coverage. Ensure the gap in between boards is treated by angling the spray into the gap.
Always treat the entire deck and apply enough coats to ensure the deck stays wet for 10 to 15 minutes after the application. 

To ensure the treated surface stays wet for 10 to 15 minutes apply a second and third consecutive coat of Bio-Shield to re-wet the timber.

Planters, steps, railings, either glass or timber can also be safely treated with Bio-Shield.
The timber may change to an orange-brown color - this is normal and the discoloration will fade over 24 hours.
Flush down any plants affected by overspray, using clean water.

Clean Up

Bio-Shield acts to kill the moss, algae and lichens on the timber over the next 2 to 4 hours. After a few days there will be visible color changes to the dead moss and lichen growths.  Black algae does not change color. The treated surface will begin to clean up after 3 months as the dead growths begin a natural breakdown to be washed away by rain.  The clean up will continue over 12 months providing the treated surface is exposed to rainfall.

On a neglected deck with heavy black algae, some hosing and brushing may be required to loosen the dead algae that lie within the timber fibres. We recommend, after  2 to 3 months,  hosing and agitating the deck along the grain with a stiff bristle broom.  Flush the deck with clean water to remove any sludge. This can be done during rain to ease the physical effort.


It is best to reapply Bio-Shield® at the first signs of re-growth. Typically this will be every 6 to 12 months on timber depending on micro climate around the deck and rainfall. 
Best practice would be to respray the deck just as the regrowth's become visible again.
On clean deck with light regrowth such as green algae, the application will be easier, faster and use less diluted solution; any new growths will die off and the deck will clean up quickly.

Once the surface is clean, Bio-Shield® will give optimal results with regular treatments.