Oamaru stone care & maintenance | Re-whiten & waterproof Oamaru stone

Oamaru stone cleaning and sealing is a maintenance that is necessary for both new home builds & existing structures in need of maintenance to re-whiten the Oamaru stone where the growth of moss, mould & lichen has caused the stone to take on a dark green or black appearance.

"Its important you maintain and care for Oamaru stone to keep its natural white and creamy colour, when in shady and damp areas the stone is at great risk of discoloration from moss & mould growth"

Quality of finish and how close to the original condition will vary on the current state of stone and length of time the moss has been growing. 

It is important to seal Oamaru stone structures due to the stone's water absorbent characteristics, this means it will soak up any moisture and become a very hospitable environment for moss, mould & lichen to grow if not correctly sealed. This water absorbent characteristic can also cause freeze/thaw damage over winter if the stone has not been waterproofed properly as water inside the stone expands and causes chipping.

By sealing new Oamaru stone structures and buildings immediately and keeping the stone waterproofed you can prevent damage and maintain its beautiful appearance throughout its life. For structures that are already growing moss & mould the cleaning process can renew its look prior to sealing.

When treated by Stratacote products the Oamaru stone coating can last for over 10 years!

Before & After Oamaru stone re-whitening treatment
Before & after the re-whitening treatment

Oamaru stone house after a Stratacote clean & seal
Protect your stone from day 1 with our sealer!



Available in 5L or 20L containers. Hypastat is a DG product.

Agent Blue

Available in variety of concentrates to suit your application.


Water-soluble impregnating agent for masonry.


Water based silicone water repellant coating for all masonry. 


This is a step by step guide to your Oamaru stone cleaning & sealing project. If you'd like further help please feel free to Contact Us with the details of your project for any advice and guidance.

✓ Spray on Hypastat using a hand garden sprayer with 40 degree course wetting nozzle, and leave on for a minimum of 30 mins. Always keep your sprayer nozzle at least 400mm away from stone.

– Mix at a ratio of 1:2 with water. i.e. 20L
Hypastat is mixed with 40L water, so will make 60L. Coverage 240m².
– Once mixed this will cover approx. 4m² per litre.

✓ Rinse off using a low pressure water blaster no more than 2500 psi, and preferably a wide fan nozzle, ie: 40 degrees. Always keep your sprayer nozzle well back, for example, at least 400mm away from stone, moving left to right, top to bottom. Ensure you have a clean, dry surface before continuing.

✓ Optionally you can spray Agent Blue Moss & Mould Kill onto the stone. No need to rinse the stone as the product works away over that time under the sealer to prevent any regrowth before the sealer is dried.

✓ After ensuring surface is dry, apply the Nanocote or Aquaseal-WB using a hand garden sprayer. To decide which sealer to use on your stone please refer to the pros and cons listed on the next page for Aquaseal-WB and Nanocote.

Aquaseal-WB Sealer application

Not sure which sealer to use? Compare Aquaseal and Nanocote here.

Aquaseal-WB prevents dampness and mould on internal walls, helps in the prevention of freeze/thaw damage on porous surfaces by stopping ingress of moisture.

Aquaseal-WB can be applied to a dry or slightly damp surface.

– Mix at a ratio of 1:14 with water. 1L of
Aquaseal-WB is mixed with 14L of water, so makes 15 litres of usable solution.
– Once mixed this will cover approx. 3m² per litre.

Nanocote Sealer application

Not sure which sealer to use? Compare Nanocote and Aquaseal here.

Nanocote is designed as a water-soluble impregnating agent for masonry that chemically bonds with masonry substrates and becomes invisible once dry. Its penetration and subsequent chemical reaction with the surface allows it to provide long term protection by significantly reducing the ingress of liquid water and any dissolved salts and contaminations that the water may carry.

Nanocote sealer is water repellent so it can’t be recoated effectively once it is dry. Therefore to get enough penetration we usually recommend spraying over the same area twice while the first coat is still wet, starting from the bottom of the stone and then coming down from the top of the stone is a good way to ensure this. This ensures the same area is given 2 coats while the first coat is still wet, which allows plenty of opportunity to coat all areas and penetrate the stone.

– Mix at a ratio of 1:9 with water. 1L
Nanocote is mixed with 9L water, so will make 10L. Total coverage 50m².
– The surface must be completely dry before applicating the
Nanocote on the Oamaru stone.
– It’s best to work in small sections and spray the same area 2 times, spraying the second coat immediately after the first coat, while it’s still wet. For example, pick a section 4 bricks wide, spray left to right, top to bottom, then recoat immediately before moving to the next section.
– Once mixed this will cover approx. 5m² per litre (or 200ml per m²).



See if your Oamaru stone needs to be treated by conducting the splash test mentioned in the blog link below:

7 Tips for care and maintenance of Oamaru Stone

Talk to the Stratacote team and share the details of your job with us below, for advice on use of our Oamaru stone care products to keep your Oamaru stone home looking its best!


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