Cleaning Clay and Terracotta Roofs

How To Clean Clay and Terracotta Roofs with Bio-Shield®

Including cleaning of:

  • Winstone Clay Tiles
  • Wunderlich Clay Tiles
  • Marseille Clay Tiles
  • Portuguese Clay Tiles
  • Terracotta Paving Tiles and Brick Pavers

Should I water blast or use Bio-Shield to clean a clay tile roof?

Clay tiles are one of the few roofs that can be waterblast cleaned without damaging the surface - testament to the quality and durability of these tiles. Water blast cleaning can however damage the mortar work, especially on older roofs with sand/cement pointing. Waterblast cleaning should be done as part of restoration work on these roofs.  Clay tile roofs will leak when water blast cleaned.

If you do intend to waterblast a clay tile roof, the best way is to apply Bio-Shield before the waterblast to kill and soften the growths.

Lichen and algae breakdown the surface of clay tiles and attack the mortar joints. Over time the surface damage becomes apparent on these tiles and they become progressively harder to get clean without water blasting.
A clean clay tile roof will dry out faster, and reduces spalling and breakdown, extending the service life.

The best method for cleaning and maintaining clay tile 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 clay tile roof maintained in a clean condition with Bio-Shield will also prevent the build up of dead moss, 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 Clay Tile 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, salts, 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 Winstone Clay Tile Roof
Bio-Shield - Lichen, Moss and Algae on Winstone Clay Tile Roof
Winstone Clay Tile 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.
Clay tiles are also extremely slippery and dangerous to walk on unless completely dry.
If you cant carry out the application with the Jet-Stream from a ladder, get professional contractors with clay tile experience
If the application will be done on the roof, always have a safety rope and harness attached to a solid anchor point
We have an application service here at that will quote on treating your roof.
From around $350 the work can be done with no risk to yourself.

Walking on Clay Tile Roofs

Clay tiles are brittle and can be broken if not walked on correctly - only walk on the center ridge, bottom half of the tiles to avoid breaking them.
This is the strongest part due to the design and is supported by both the tile and tile batten underneath.
Avoid the overlap cover of the tile, this is the weakest part and will break the corner off the tile.
Dry the soles of your shoes before walking on the roof and ensure they stay dry throughout the work.
Do not walk on any areas sprayed with Bio-Shield until they are dry.


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. Coloursteel 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 15 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 Litre65 ml1.065 Litres
10 Litres650 ml10.65 Litres
15 Litres975 ml15.97 Litres
20 Litres1.3 Litre21.3 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 i.e. at 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 and any moss growing in the laps or bottom edge are saturated, giving penetration of the solution to the base and achieving a good kill.

Apply a second lighter coat after 10-15 minutes, once the roof is dry enough to walk on.
This coat is to just rewet the surface.

Chimneys, solar panels, spoutings, vent pipes and skylights can be safely  treated with Bio-Shield® 

Clean Up

Over the next few days the lichens and moss will begin to change color as they  die off.
For the initial clean up it may take 6 to 12 months for the roof to fully clean up 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 with a single coat 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 pipes that discharge water onto the roof, will show re-growth's first and can be spot treated as required.