Cleaning Decrabond, Gerard Roofs and Asphalt Shingle Roofs

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)
  • All asphalt/fibreglass shingles.

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

Tile surfaces can be damaged when water blasting stone-chip coated tiles to remove algae, moss, and lichen. The pressure required to fully remove lichen may exceed the stone chip's bond strength with the substrate, causing it to fail and give rise to long-term damage.

The best method for cleaning these roofs is to use a mild exterior cleaner.

A simple application will kill and remove the growths and keep the surface clean for extended periods without damaging the tiles.

Light applications of an exterior cleaning solution at the first sign of re-growths will provide a quick clean up and keep the surface clean for an extended time.

A clean roof protected with an exterior cleaning solution will also prevent moss, algae and lichen debris building up in the spouting which can reduce rusting and blockages that cause spouting to overflow in heavy rain.


Did you know that the majority of falls that lead to the emergency room in New Zealand are caused by homeowners working on their roofs over the weekend?

If you would rather not take the risk and leave it to the professionals, we offer an application service. Head to for more information.

If you still want to DIY your roof clean, be cautious and use a safety rope fastened to something sturdy to prevent ending up on the ground.

Walking on Tile Roofs

The best location to walk on pressed metal tiles is in the centre of the tile at the bottom edge, in the "pan" of the tile. This is due to the design and is supported by both tile and tile batten below.

Avoid the tile ridge or high section of the tile; this is the area where the tile is weakest, and it will bend and dent easily, resulting in a fatigue crack developing at the apex of the dent. This will leak.


Preparation is crucial for a successful do-it-yourself project. Following these easy guidelines will guarantee a professional looking finish and long-term protection against algae and lichen growth, which can cause damage to your roof.

Place your ladder on a solid foundation at the point where the distance between roof and ground is smallest. The ladder's base should be set 1 metre from the spout for every four metres in height. To make entering and exiting the roof as safe as possible, make sure that the top of the ladder reaches at least 1 m above the edge of the roof.

The risk of breaking PVC spouting or deforming metal spouting is reduced by placing the ladder against the brackets.

The first ascent should be made with a bungee cord or luggage tie to keep the ladder from slipping, and it should be connected to the spouting as soon as possible. Colorsteel or painted spouting should have some sort of barrier between it and the ladder to prevent scratching of the paint.

Remove debris such as tree leaves. Overhanging trees may be trimmed back to assist the roof in clearing up and maintaining its cleanliness. The roof surface can be either dry or damp.

Before commencing, check local council regulations for discharge of wash water into the stormwater system.

If your house is on tank water, disconnect the tank from the roof. For 2 to 4 weeks, it must be disconnected until enough rain has fallen to remove all traces of exterior cleaner from the roof. Until then, do not reconnect the tank.

Check the weather forecast or the rain radar to see if it's going to rain after application. Higher temperatures may also assist in biocidal action.


If you have a respirator, put it on now. Also, don't forget gloves, soft-soled shoes, and long pants. If you don't have a respirator, try to stay upwind when applying the solution. On a warmer day, evaporation of the solution might produce vapour.

The best time for application is on an overcast day, any time of the year. If it is summer and the day is likely to be hot or sunny, early mornings and late afternoons are best to prevent the solution from evaporating too quickly after application.

Fill your sprayer with the correct dilution of your chosen exterior cleaning solution and pump it up to pressure.

Dividing the area to be treated into sections makes application easier.

The rows of tiles can act as a great guide for evenly application of the solution. Apply to 2-3 rows at a time.

Begin at the highest point, which is usually the ridge tiles, and work your way down the roof in slow, even strokes, to ensure saturation. Ensure that any lichen growths are fully saturated. This will ensure that the solution reaches the roots and results in a successful kill.

It is important to always treat the entire roof, darker coloured roofs will hide the widespread black algae growths. The surface should stay wet for 5-10 minutes after application. Chimneys, vents, solar panels and skylights can be treated with an exterior cleaning solution while you are on the roof.

If you've covered everything properly, the runoff should be an orange-brown shade - this is a great indication that the exterior cleaning solution is attacking the algae cell walls and that their death is unavoidable.


The surface will clean up over the next 3 to 12 months if it is exposed to rainfall, but a roof with heavy algae and lichen may take up to 12 months to fully clear.

The more rain the surface receives, the faster it will be cleaned.

The exterior cleaning solution should be reapplied as soon as possible after re-growth has begun. This is usually every 2 to 3 years.

A good practice would be to have the roof re-treated just as the growths become visible again. This will result in a quicker clean-up process, resulting in an efficient maintenance process.

After the surface is cleaned, an exterior cleaning solution should provide optimum results with regular maintenance treatments. This will protect the decorative and protective stone-chip covering from damage and decay caused by fungal and lichen growths as it builds up over time.