Newly laid patio with Indian sandstone with marks appearing

[ShaunP]

Hi

I’ve recently had a sandstone patio laid on compacted type 1 with wet bed by a landscaper. The last few days white marking is appearing on the slabs, if the slab is wet, these marks appear back really quickly, has anyone any idea what they are, what caused them and if they can be removed?

thanks

 

[Celeronmanuk]

Looks like effervescence to me and will weather out eventually. The manufacturers instructions will likely warn of this.

 

[Mike13]

efflorescence is the word, evervescence is what alka-seltzer does. Try a good scrub and with dilute brick cleaner (try on an offcut first) then immediately rinse down so it doesnt mark the stone.

 

[Celeronmanuk]

Be very careful with acidic cleaners, you can cause damage to sandstone. I'd suggest leaving it to weather out as per manufactures guidance.

e.g.

"Although most commonly associated with concrete paving products, efflorescence can also affect natural stone when it is laid on a full mortar bed. Limestone products can be particularly susceptible. This is a temporary phenomenon caused by the chemical reaction between water and cement, which will weather out naturally and does not damage the paving. There are many efflorescence removers available for purchase on the market, but we recommend it is left to weather out naturally to avoid any damage to the surface of the paving. Efflorescence is not a fault of the manufactured or natural stone."

http://www.castacrete.co.uk/guidance-and-tips

 

[ShaunP]

Thanks, one of the slabs cracked so I lifted it up. Is this what a full bed of mortar should look like?

 

[Mike13]

That cracked because it wasnt a full bed of mortar, the marks are where it is touching the mortar I think

 

[Celeronmanuk]

Agreed, bed looks really poor. Ideally slabs should be slurry primed on the back too. Whats happening about the pointing?