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Cleaning Concrete and Clay Tile Roofs

Roof Wash - How To Clean Concrete and Clay Tile Roofs with Bio-Shield®
Including cleaning of:

Modern concrete tile roofs - Monier, Boral, Bristile.

Clay tile roofs - Marsellie, Bristile, Wunderlich, Monier.

Slate roofs.

Should I water blast clean or use Bio-Shield to clean a concrete tile roof?
Water blasting 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.
This is a time consuming, expensive, and ultimately futile way to clean these surfaces: if they are not sterilised in conjunction with water blasting, the spores within the tiles will quickly regrow and discolor the roof again. Older concrete roofs can also begin to leak from small pinholes or porous areas in the tiles that are opened up by the high-pressure water jet.

The best method for cleaning and maintaining concrete and clay tile roofs are exterior cleaning solutions like Bio-Shield®.

A simple 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 re-growths will effect a rapid clean up and keep the surface clean again for an extended period.
A tile 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 cause spoutings to overflow in heavy rain.

Why choose Bio-Shield® for your DIY Concrete Tile Roof Cleaning?
Bio-Shield® has been developed through 30 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 means it will cost less per diluted litre and cover more area at a lower cost.

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How to clean Concrete and Clay Tile (Terracotta) Roofs - 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.
We have an application service here at that will quote on treating your roof. 
From around $250 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 edge.  This is the strongest part of the tile due to the design and it is supported 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 by Roof Wash Ltd, 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 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 made to tie it to the spouting, ideally with a bungee cord or luggage tie to prevent the ladder from slipping.  Coloursteel or painted spoutings should have some protection placed between the spouting and ladder to stop  scratching of 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 help keep it clean.
The concrete roof surface can be either dry or damp.
Clay tiles must be dry to avoid slipping

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 of water.
Do not reconnect the tank until the water is free of frothing or odour.

Check the weather forecast, or rain radar - brief showers after application on a porous surface 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 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.

Bio-Shield Mixing Ratios
Clean Water Bio-Shield Concentrate Diluted Bio-Shield
1 Litre 50 ml 1.05 Litres
 10 Litres 500 ml 10.5 Litres
15 Litres 750 ml 15.75 Litres
20 Litres 1 Litre 21 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.

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.
On concrete tiles: Start at the highest point the ridge tiles,
On clay tiles: Start at the lowest point to avoid walking on the wet and slippery surface.
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 to 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 is also 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 to stay 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 orange-brown colour - this is a good sign and indicates that the Bio-Shield® has penetrated the cell walls of the fungal growths and that their death is unavoidable.


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 orange-brown colour will fade and the moss growths will begin to turn brown as they die off.
2 to 3 weeks after application the moss growths should be entirely brown and any lichen present will have undergone a slight color change. The black fungal growths will not change color, but will simply fade away.
If there are any green patches in the moss growths, the Bio-Shield® was applied too lightly to saturate the growth to the roots.  Spot spray these areas with the leftover 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 re-growth. Typically this will be every 2 to 3 years.
Best practice would be to have the roof re-treated just as the growths become visible again.
Application will be easier, faster and use less diluted solution; any new growths will die off and the roof will clean up quickly.

Once the surface is clean Bio-Shield® will give optimal results with regular treatments.  This will protect the cement-based color-coating from damage and premature erosion caused by a build up of moss, fungal and lichen growths.
Discounts, special offers, new arrivals
Bio-Shield has been developed and used commercially for over 38 years to successfully remove moss, algae and lichen from just about every exterior surface on domestic, commercial and industrial properties. 
The same high quality product is now available for DIY and commercial use on homes and businesses throughout Australia
We are committed to supplying our customers the best outdoor cleaning product at the best price, complimented with the best technical advice and support in Australia.

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