Cleaning Colorsteel Colorbond and Colorcote Roofs

Should I water blast clean or use an exterior cleaning solution to clean a colour coated roof?

Water blasting colour coated roofs to remove moss, algae and lichen growths has the potential to damage the surface. The pressure required to fully remove lichen will remove the protection offered by the oxidised surface layer, reducing the thickness of the coating and exposing the un-oxidized paint film to sunlight and weathered. Uneven removal of this layer on older roofs may leave a striped pattern on the roof after cleaning. 

The best method for washing and cleaning these roofs is to use a mild exterior solution. We recommend the use of Bio-Shield for this.

A simple application will kill and remove the growths and keep the surface clean for extended periods.

Regular lighter applications of a mild exterior solution at the first sign of re-growths are recommended. This can minimise the amount of time it takes to clean up and keep the surface clean for an extended period.

A roof kept clean with a good mild exterior cleaning solution will also minimise the build up of debris from moss algae and lichen growths, This can reduce rusting and potential blockages that cause spouting to overflow in heavy rain.


The most common cause of falls in New Zealand is from homeowners working on their roofs during the weekend. If you have any doubts about your ability to carry out this work safely then do not attempt it.

We have an application service here at that will quote on treating your roof. From around $250inc GST you can keep yourself safe and leave it to the professionals.

If you still wish to go ahead and do the work yourself, please use caution while performing this activity and secure a safety line to something sturdy before beginning work on the roof.

Walking on Tile Roofs

To protect pressed metal tiles from being dented, the safest place to your feet is the centre of the tile at the bottom edge in the 'pan' of the tile. This part of the tiles is supported by both the lower tile and tile batten beneath it, making it the tile's most robust section.

Avoid the ridge of the tile, which is the weakest portion and will easily bend and buckle, creating a fatigue fracture at the top of the dent. This will leak.


Preparation is the key to a successful do-it-yourself project. Following these simple instructions will guarantee that your roof has a professional appearance and long-lasting protection against lichen and moss regrowth.

At the place where the distance between roof and ground is shortest, set up your ladder. The ladder's base should be 1 metre from the spouting for every four metres in height. To make getting on and off the roof as safe as possible, make sure that the top of the ladder reaches at least 1 metre above the edge of the roof.

Placing the ladder next to the spouting brackets will decrease the risk of breaking PVC spouts or deforming metal spouts.

To prevent the ladder from sliding, make your first journey up it to attach it to the spout, preferably using a bungee cord or luggage tie. To avoid scratching of the coating, colorsteel or painted spouts should have some barrier between them and the ladder.

Remove any loose debris, tree leaves, soil, and so on from the roof surface. Cut back overhanging trees to help the roof clean up and keep it clean.

The roof surface can be either dry or damp.

Check your local governing body's rules on discharging wash water into the stormwater system.

If you're on tank water, disconnect the tank from the roof. It'll need to be disconnected for two to four weeks while the roof is cleaned by enough rain to remove all traces of the exterior cleaning solution from the run of water. Do not reconnect the tank until the water is free of frothing or odour.


From here, it is recommended you put on a respirator, along with gloves and soft-soled shoes or pants. If you don't have a respirator, try to stay upwind while applying the solution. On a hot day, the solution will evaporate, resulting in vapour that should be avoided wherever possible.

The best time for application is on an overcast day at any time of the year,.If it is forecast to be hot or sunny, early morning or late afternoon is another ideal time. This slows evaporation and speeds up the treatment process.

Fill your sprayer in accordance with the instructions on your chosen exterior cleaning solution and pump it up to pressure.

Divide the area that needs to be treated up into sections to make application easier.

Use the rows of tiles to help guide you to a spray path of 2 to 3 rows of tiles.

Begin at the roof's highest point and work your way down, applying a saturation coat to the surface in even strokes. Once you've finished spraying this section move down the roof and apply the next three rows.

Ensure the lichen growths are saturated through to the tile to ensure penetration of the solution to the roots and achieve a good kill.

It's always best to treat the entire roof even if it looks clean. Dark-colored roofs will hide the black algae growths. A partial application will cause a patchy, uneven clean up.

To keep the treated area wet for 10 to 15 minutes, apply a second light coat of your chosen exterior cleaning solution to any black algae growths.

This 2nd coat is best applied as soon as the first coat has dried enough to allow safe walking on the roof.

Chimneys, vent pipes,solar panels and skylights can also be treated with an exterior cleaning solution while you are on the roof.

There may be a visible orange-brown runoff - this is a good indication that the exterior cleaning solution is breaking the algae cell wall - cell death is unavoidable.


The treated surface will clear up over the next few months given there is enough rainfall. It should be noted that particularly dirty surfaces may take as long as 12 months to clear up.

The more rain the surface receives, the faster it will clean up.

It is best to reapply a good exterior cleaning solution at the first signs of regrowth. This will typically be every 2 to 3 years.

We recommend having the roof re-treated just as the growths become visible again. This will result in an easier, faster application, require less cleaning solution, and any new growth will die off and clean up quickly.

Once the surface is clean, your chosen cleaning solution will give optimal results with regular maintenance treatments. This will protect the factory colour-coating from damage and premature erosion caused by a build-up of moss, algae and lichen growths.