Roof Cleaning - How to Clean a Concrete or Clay Tile Roof with Bio-Shield

How To Clean Concrete and Clay Tile Roofs.

Including Cleaning of:


Modern Concrete Tile Roofs - Monier, Ross, Boral, Taylor.
Clay Tile Roofs - Winstone, Marsellie  Wunderlich, Monier.
Obsolete Concrete Tile Roofs - Atlas, Besser, Cowperthwaite, Craig,
Slate Roofs


Waterblasting concrete and clay tile roofs to remove fungal, moss and lichen growths will damage the surface and  prematurely erode the factory applied cement based colour coating on modern concrete tiles.
It's a time consuming and expensive way to clean these surfaces and if they are not sterilsed in addition to waterblasting the spores within the tiles will quickly regrow and discolour the roof again.
Older concrete roofs can begin to leak from small pinholes or porous areas in the tile that are opened up by the high pressure water jet.

The best solution to clean and maintain concrete and ashpalt is Bio-Shield.

A single application 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 regrowths will keep the surface clean with casuing damage.
A tile roof maintianed 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 cause spoutings to overflow in heavy rain.

No more waterblasting or scrubbing.


Most falls from roofs are by homeowners working on thier 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.
We have an application service here at that will quote on treating your roof.  For around $200 the work can be done with no risk to yourself.

If you still want to do it by yourself then please be careful and use a safety rope secured to something solid to prevent a fall.

Walking on Tile Roofs

To prevent damage to the tiles the best place to walk is in the centre of the tile at the bottom egde.  This is the strongest part of the tile due to the design and it is suported by both the tile and tile batten underneath.
Avoid the overlapping outside edge of the tile, this is the weakest part and breaks easily.
If you have a Winstone or Marseille clay tile it would be best to have this type of roof done professionally.  These tiles break easily and will leak if not replaced.


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

  • Place your ladder on firm ground at the lowest point possible between the ground and roof level. 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 possibilty 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 lugage tie to prevent the ladder from slipping.  Coloursteel or painted spoutings should have some protection placed between the spouting and ladder to stop  scratching the coating.
  • Remove loose debris, tree leaves, dirt etc, from the roof surface. Cutting back overhanging trees will help the roof to clean up and then keep it clean.
  • The roof surface can be either dry or damp.
  • Check Council 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 of water.
    Do not reconnect the tank until the water has no frothing or odour.

  • Check the weather forecast, or rain radar - brief showers are OK after application on a porous surface and will assist the Bio-Shield to work faster.
  • Air temperature above 10 degrees C.particularly in the South Island
  • Premix the Bio-Shield ® 1 part to 20 parts water in the sprayer or a larger bucket.
    The average roof on a 3 bedroom house will take 60 to 80 litres of Bio-Shield applied with a garden pressure sprayer.

50    mls of Bio-Shield 1 Litre of Clean Water
250  mls of Bio-Shield 5 Litres of Clean Water
500  mls of Bio-Shield 10 Litres of Clean Water
750  mls of Bio-Shield 15 Litres of Clean Water
Bio-Shield Mixing Ratios


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

  • Fill your sprayer with the premixed Bio-Shield solution and pump it up to pressure.
  • Breaking the area up into sections makes application easier. 
    Use the rows of tiles to help guide you.
  • 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.
  • Any moss growth growing in the tile laps will need to be saturated with Bio-Shield to ensure penetration to the roots and achieve a good kill. I do this by placing the nozzle of the sprayer  directly into the tile lap and injecting it into the clump.
    Some tiles in damp areas will also have moss growths on the bottom edge of the tile so ensure this saturated
  • When you have finished treating the section look back over it and respray any patches that have dried out.  This drying out can be caused from the application not saturating the surface.
    Aim for the surface staying wet for 5 to 10 minutes after application.
  • Chimneys, vent pipes and skylights can all be treated with Bio-Shield while you are on the roof.

  • If you have achieved correct coverage the runoff should have an orangey - brown colour - this is good and indicates the Bio-Shield has penetrated the cell walls of the fungal growths and nothing will save them from being killed. 


    Any leftover Bio-Shield solution will keep indefinitely and can be kept aside to use as a spot spray to touch up any areas that need it.
    Over the next few days the orangey brown colour will fade and the moss growths will begin to turn brown as it dies off.
    Two to 3 weeks after application the moss growths should be entirely brown and any lichen present will have undergone a slight colour change. The black fungal growths odes not change colour, it will just fade away.
    If there are any green patches in the moss growths the Bio-Shield was applied to lightly to saturate the growth to the roots.  Spot spray these areas with the left over Bio-Shield.


The treated surface may clean up over the next few months providing it is exposed to rainfall, however it would not be unusual for a  dirty roof to take up to 12 months to fully clean up.
The more rain the surface receives, the faster it will clean up.
It is best to reapply Bio-Shield at the first signs of regrowths. Typically this will be every 2 to 3 years.
Best practice would have the roof re-treated just as the growths become visible again.
Application will be easier, faster and use less material and then any new growths will die off and the roof will clean up quickly.

Once the surface is clean Bio-Shield® will give the best results with regular removal treatments.  This will protect the cement based colour coating from damage and premature erosion caused by a build up of moss, fungal and lichen growths.

Why choose Bio-Shield® for your DIY roof cleaning?

Bio-Shield® has been developed through 27 years of use in a demanding commercial environment so it works extremely well.
Bio-Shield is high quality product, its bio-degradable, not caustic and contains no bleach.

                                               More Cleaning - Less Money

Bio-Shield's high concentration of active ingredients and unique surfactants give you more usable product than similar cleaners at a lower cost per diluted litre.



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The information contained in this page are intended solely for the use of customers who have purchased Bio-Shield®
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