Why experts swear by milk for cleaning stone floors – and yes, it really works

If you prefer to use a natural cleaner, there is one rather surprising household commodity that can be used to clean stone floors. Milk. 

Architect and renovator Neil Mackay, used skimmed milk to clean the 18th-century flagstones in the Oxfordshire cottage he renovated. 'As I understand it, the casein in the milk forms a weak binder on the surface of the flagstones, giving them a slightly polished sheen, and keeping down dust,' he says. 

'It works best on smooth stones, with a fine, close surface texture. On a coarser stone the effect is a little different, and the stone will temporarily look darker.

'I just washed the floors with warm water and a stiff brush, then scrubbed them again with skimmed milk and let it dry. For a short while it smelled a little milky, but not unpleasantly so. Once it dried, the smell rapidly faded.'

• See: How to clean stone floors – restore their natural shine

How do you clean stone flooring with milk?

In its Caring for Old Floors technical notes, The Society for the Protection of Ancient Buildings (SPAB) says the use of sour (unpasteurized) milk to clean stone floors is mentioned in 19th-century household manuals. Applied sparingly with a rag, it 'can bring up a soft sheen and a degree of protection to the surface of fine-grained stone with an established patina'. However, SPAB warns against using milk to clean absorbent or damp stone as it may leave a stain. 

With all cleaning products, natural or not, it's best to check with your flooring provider and test on a small, unobtrusive area of the floor first. 

'SPAB's technical notes specifically mention unpasteurized sour milk,' says architect Neil Mackay. 'As pasteurization can denature the milk proteins. But I used pasteurized milk with no problems - it's difficult to get it unpasteurized. I'm not sure why it would need to be soured, but I suspect that it may be for the acidity, which might act as a mild cleaning agent. 

'It may also be that it breaks down some of the fats and sugars in the milk, preventing them from becoming unpleasant later. Skimmed milk is used for a similar reason. Or it may be that it was just that nobody would have wanted to waste fresh milk, and prior to refrigeration there was always plenty of soured milk around.'