Indian sandstone have white marks

Why Does my Indian Sandstone Have White Marks on it?

Post by
Scott D. Renwick
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You’ve just had your Indian sandstone patio laid and it’s full of white residue. Don’t panic, it’s perfectly natural. Let me explain.

This wasn’t so common in the past. Indian sandstone used to come in much thicker slabs. This varied considerably but generally, they were significantly thicker slabs.

We’ll get back to this point in a moment. Now we’re going to talk about a chemical process called efflorescence.

What’s efflorescence Scott? I hear you all ask in unison.

Let me explain what efflorescence is to your curious mind.

Indian Sandstone Have White Marks


In chemistry, efflorescence is the movement of a salt to the surface of a porous material (Indian Sandstone), where it forms a coating. This coating appears as white marks over your slab.

In the case of Indian sandstone, what is happening is that the porous slab is drawing up the moisture of the wet mortar mix upon which the slabs are laid. This is pushing out the salt from the stone. Leaving it to show up on your new beautiful slabs.

Now, remember the point I made earlier about the slabs being thicker in the past. This made a difference because the minerals had farther to travel to reach the surface. This made it a less likely occurrence. But now the Indian sandstone slabs are calibrated and much thinner, the chemical process is more commonly visible.

What can you do about efflorescence on your Indian sandstone? 

The first thing to do is wait. As the salt comes out of the stone and washes away, the stone will reveal its true majestic tones and colors.

Secondly, if it does not come off there are efflorescence cleaners on the market to help with the removal of the salt – like this one from our good friends at Tile Market. But we recommend waiting a couple of weeks at least before you start playing around with chemical cleaners, as they can result in different problems if not used correctly.

Prevention is Better Than…


Finally, the most important thing you can do is prevent this from happening in the first place.

How do you do that Scott? I hear you ask again in unison. You lot are an enthusiastic bunch of learners.

Before laying your Indian sandstone, the slab itself should be primed with a slurry solution that is coated onto the back of your slabs.

This hardens and forms a barrier between the slab and the mortar mix upon which it is laid. As well as this the priming slurry will draw the minerals downwards away from the surface, preventing the upward drawing of the salt minerals to the surface after it is laid.

Unfortunately, most landscape service providers will not do this. At SAS Landscapes as natural stone specialists, we always ensure we put on that priming slurry to the back of the slabs before laying them, ensuring the somewhat temporary problem of efflorescence does not persist and you are left with an excellent natural stone patio.

I know what you’re thinking now!

How can I get SAS Landscapes to lay my Indian sandstone patio?

The answer is simple!

Contact SAS Landscapes today for a quote:
083 137 7834

Photo by Yogendra Singh on Unsplash

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