cleaning cast stone

Cleaning Cast Stone | A complete Guide

Cleaning Cast Stone ensures it stays looking as fabulous as the day it was installed. At the same time, effective Cast Stone maintenance provides long-lasting protection.

It’s a question we’re often asked. How do I keep my cast stone looking as good as when it was first installed? Staining from whatever source can easily compromise the appearance of cast stone. And while weathering and aging is a feature than many people look for, others value the original colour and pristine appearance of cast stone.

So, in answer to this common question, here’s our complete guide to cleaning cast stone and effective cast stone maintenance. You’ll find that following these simple processes is easy and straightforward, and will refresh the appearance of your cast stone.

Principles of Cleaning Cast Stone

But before we take a good look at the different methods of cleaning cast stone, it’s important to remember a few key principles. They’re an investment in quality, so really worth knowing.

The first of these principles is to know that cast stone behaves similarly to natural stone. This means that any cleaning can expose the underlying cast stone which may have weathered differently, causing subtle changes in colour. There’s no need to worry though; cleaning gently will remove this issue.

It’s also important to remember that although cast stone may get dirty, this is usually unlikely to cause any particular problems. The only exception is if dirt is causing decay to the surface, or staining the underlying stone, especially at street level. Should this have happened, it may be appropriate to arrange some remedial action.

Finally, we always recommend testing cleaning cast stone on a small area. This entails testing your cleaning method out on a small, inconspicuous area before continuing to clean any visible areas.

All of this being understood, we can now take a closer look at the different methods of cleaning cast stone and effective cast stone maintenance.

Dry Brushing Cast Stone

First, let’s take a look at dry brushing cast stone. For the dry brushing cast stone cleaning process, you’ll need either a stiff bristle or fibreglass brush. Brush the cast stone to remove any light deposits such as mortar. It’s never a good idea to use scrapers, or metallic or wire brushes. That’s because they will mark the face of the cast stone, and this damage will be permanent.

Water Washing Cast Stone

Next up, let’s look at water washing cast stone. Because most dirt is water soluble, cast stone cleaning with water is a popular option. Water washing is also a very simple process. That’s because all you need is a bucket and brush, and a low-pressure hosepipe.

High-pressure hoses or jet washes should not be used for cleaning cast stone as it can result in damage to the fine surface of the cast stone units or the mortar joints. For more stubborn stains, use a mild detergent like sugar soap. You can add this to the water, before making sure it is thoroughly rinsed off. A note of caution: avoid saturating the cast stone because it can become stained as the dirty water dries off. Another issue of high saturation is the efflorescence that can occur as soluble salt in both the cast stone and mortar joints is reactivated by water. So, care is required. Just remember the mantra: no saturation.

Using Chemical Cleaners 

Chemical cleaning has always been one of the most popular methods for cleaning cast stone. You can use hydrochloric acid – or indeed any of a number of easily available proprietary cleaners – to remove salt deposits, mortar stains and lime blooms. To get the right mix, simply dilute the hydrochloric acid in water to no more than 10% of the volume. We always recommend you use proprietary cleaners in accordance with the manufacturer’s instructions.

Care should always be taken when using chemical cleaners. That’s because chemical cleaners can in some cases change both the colour and the texture of the cast stone. As a result, we recommend that whole stones and all adjacent areas are treated to maintain a uniform appearance. Also, for effective cleaning and to prevent burning of the surface, the cast stone and surrounding surfaces – especially below where you’re cleaning – should be wetted with water before you apply any acid-based cleaning fluids. That’s because cast stone will always absorb a small amount of liquid so it’s essential to wet the stone first.

Prepping and finishing Cast Stone

Whichever method of cleaning cast stone you choose, prepping before you start and finishing with a few key processes at the end of cleaning will help provide the best results.

Before starting: Remove moss, lichen and built-up dirt with a dry sponge or a soft bristle brush.  Always take great care not to cause damage to the surface of the cast stone surface by rubbing too harshly. Be sure to protect the area you’re working in with plastic sheeting or similar. Remember to wet first with lots of water but avoid over-saturating.

Next, it’s time for cleaning using your preferred method from those described above. Often, this will be enough to improve the appearance of your cast stone, especially with newer designs, or those that have not been exposed to months of harsh weather. The cast stone must be cleaned individually; attempting to clean multiple units may cause acids or other cleaning materials to be left for longer than needed, which may result in damage to the surface of the cast stone.

After cleaning: Leave to dry and check results if the stain has not completely disappeared and the surface of the stone still feels smooth and not gritty then a further application is ok.  Once satisfied with the results clean the whole unit. Remember to rinse after using plenty of water. Clean and remove from area any excess liquid by use absorbent granules.

Keeping your stone looking like new, for longer

If you would like your cast stone to look like new for much longer, you could seal the stone after installation with a proprietary stone sealer, which would also seal the mortar joints as well. The product we recommend is called Lithofin Stain Stop, and you can see find out more here.

So, there we have it. Everything you could ever want to know about cleaning cast stone.

If you’d like any specific advice about any aspect of cast stone maintenance, please do feel free to call us on 01773 540704 or email our expert team on

In the meantime, happy cast stone cleaning, and we hope you’ll be delighted with the results.

Request a sample

If you would like to see our range of cast stone colours, you can request your free sample by clicking here.



Related Posts

GPF Lewis Case Study

Luxury bespoke ‘Cheyne Place London’ residential project (Before and after images courtesy of Google Maps) Customer: GPF Lewis – a long-standing customer since 2018. Location:

Read More