Cleaning Decrabond, Gerard Roofs and Asphalt Shingle Roofs

How To Clean Decrabond, Gerard, Asphalt Shingle Roofs with Bio-Shield®

Including cleaning of:

  • Decrabond, Decramastic, Gerard, Coronashake,
  • Oberon Shingle, Tuffcoat, Rockport Shingle, Senator Shingle, Milano Shingle
  • Metrotiles including Roman, Bond, Shake, Classic, Tudor and Royal
  • Asphalt / Fibreglass Shingles

Should I pressure clean or use Bio-Shield to clean a chip coated tile roof?

Pressure cleaning stone chip coated roofs to remove algae and lichen will damage the surface, removing the decorative and protective stone chip.
This is a time consuming, expensive, and ultimately futile way to clean these surfaces: if they are not sterilised in conjunction with pressure cleaning, the spores on the tiles surface will quickly regrow and discolor the roof again.  Most roofs will leak with high pressure water jetting.

The best method for cleaning and maintaining chip coated roofs are exterior cleaning solutions like Bio-Shield®.

A simple application of Bio-Shield will kill and remove the growths and keep the surface clean for extended periods. 
Regular lighter 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 chip coated roof maintained in a clean condition with Bio-Shield will also prevent the build up of dead moss and lichen growths and sludge in the spoutings, reducing rusting and blockages that can cause spoutings to overflow in heavy rain.

Why choose Bio-Shield® for your D.I.Y Decrabond roof 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, acids or phosphates.
The high concentration of active ingredients in Bio-Shield® when compared to other outdoor cleaners such as Wet and Forget and 30 Seconds means it will cost less per diluted litre and cover more area at  lower cost.

Bio-Shield - Lichen, Moss and Algae on Asphalt Shingle
Bio-Shield - Gerard roof before Bio-Shield Cleaning
Asphalt Shingle Roof cleaned  with Bio-Shield

Bio-Shield® Application Instructions


Most falls from roofs are by homeowners working on their own roofs on the weekend.
If you have any doubts about your ability to to carry out this work safely then do not attempt it.

Walking on Pressed Metal Tile Roofs

To prevent damage to pressed metal tiles the best place to walk is in the centre of the tile at the bottom edge, in the 'pan' of the tile 
This is the strongest part due to the design and is supported by both the tile and tile batten underneath.
Avoid the ridge of the tile, this is the weakest part and will bend and buckle easily resulting in a fatigue crack forming at the apex of the dent. This will leak.
Asphalt Shingles are very easy to walk on.  The stone chip coating provides good grip and the shingle is fully supported underneath by strong plywood sheets.


For a successful DIY job, preparation is the key. Following these simple steps will ensure a professional looking finish and long lasting protection against regrowth damaging your roof.

Place your ladder on firm ground at the point where the distance between roof and ground is smallest. For every four metres in height the ladder base should be placed 1 metre out from the spouting. The top of the ladder should extend at least 1 metre above the edge of the roof to make entering and exiting the roof as safe as possible.

Placing the ladder against the spouting brackets will reduce the possibility of breaking PVC spouting or deforming metal spoutings.

The first trip up the ladder should be to tie it to the spouting, ideally with a bungee cord or luggage tie to prevent the ladder from slipping. Colorbond or painted spoutings should have some protection placed between the spouting and ladder to stop scratching of the coating.

Remove any loose debris, tree leaves etc, from the roof surface. Cutting back overhanging trees will help the roof to clean up and help keep it clean.

Check local governing body regulations for discharge of wash water into the storm water system.
If you are on tank water disconnect the tank from the roof. It will need to stay disconnected for 2 to 4 weeks, and until the roof is flushed by enough rain to remove all traces of the Bio-Shield from the run off water. Do not reconnect the tank until the water is free of frothing or odour.

Check the weather forecast, or rain radar - no rain for 3 to 4 hours but brief, light showers after application will assist the action of Bio-Shield®

Air temperature above 10 degrees C° will help to accelerate biocidal action.

Premix the Bio-Shield® 1 part to 20 parts water in a pressure sprayer.

If using the Jet-Stream Applicator, follow the instruction on the back label.

Bio-Shield® Mixing Ratios - for Pressure Sprayers

Clean WaterBio-Shield ConcentrateDiluted Bio-Shield
1 Litre50 ml1.05 Litres
10 Litres500 ml10.5 Litres
15 Litres750 ml15.75 Litres
20 Litres1 Litre21 Litres


If you have a respirator, now is the time to put it on, along with a pair of gloves and soft soled shoes and/or a pair of long pants. If you don't have a respirator, try to stay upwind during application. Evaporation of the solution on a warmer day will generate vapour that should be avoided where possible.

Application is best done on an overcast day at any time of the year, or early morning and late afternoon in summer if a warm sunny day is forecast. This slows evaporation and speeds the treatment process.

Saturation is the Key to Success - ensure saturation of any lichen or moss

Fill your sprayer with the premixed Bio-Shield® solution and pump it up to pressure. Dividing the area to be treated into sections makes application easier. Use the rows of tiles to help guide you say a spray path of 2 to 3 rows of tiles. Starting at the highest point the ridge tiles, begin application to the surface in slow, even strokes. Allow the following stroke to overlap the previous stroke by 50% to ensure even and complete coverage. Once the row of 3 tiles is complete move down the roof and spray the next 3 rows. Ensure the lichen growths are saturated, giving penetration of the solution to the roots and achieving a good kill. Always treat the entire roof, darker colored roofs will hide the widespread black algae growths. As the roof cleans up the treated areas will be lighter in color than the untreated areas giving a patchy appearance.

Aim for the surface to stay wet for 10 to 15 minutes after application.
Chimneys, solar panels, vent pipes and skylights can be safely treated with Bio-Shield® The runoff may have an orange-brown color. This discoloration will fade over 24 to 48 hours.

Clean Up

Over the next few days the lichens will begin to change color as they die off.
For the initial clean up it may take 3 to 12 months for the roof to fully clean  as rain progressively washes the dead growths away.
The cleanup progress can accelerate in the 9 to 12 month period as the dead growths are softer and easily washed away.


Once your roof is clean, Bio-Shield will give optimal protection with regular treatments.
Best practice is to reapply Bio-Shield at the first signs of re-growth. Typically this will be every 2 to 3 years.
Two for three yearly applications will be easier, faster and use less diluted solution; any new growths will die off and the roof will clean up quickly
Any areas of the roof where birds habitually sit and areas under trees, TV aerials or vents and pipes that discharge water onto the roof, will show re-growth's first and can be spot treated as required.