The problem with contractors leaving mortar stains to dry on natural stone paving slabs, is one that for some reason continues to happen. This is basically down to poor installation, any mortar residue left on the slabs should be cleaned off thoroughly during installation and should never be left to dry on the surface of any paving material.

The next step after people find they have left mortar stains on the surface of the paving, generally around the edges of the slabs, is to try to remove these stains with a Brick Acid wash, the use of acid on natural stone will cause irreparable damage to the surface of the stone and in a lot of cases will bring the iron which is present in the stone to the surface, completely destroying the appearance of the stone.

How to remove mortar stains?

There is only one way to correctly remove mortar stains from any paving material and that is to do it whilst it’s still wet, during installation. Always keep a bucket and a large sponge with you at all times during pointing and clean up any residue as you work. It’s very simple but you would be amazed how many contractors do not work cleanly whilst pointing with sand and cement mortar. It takes no longer but will completely remove any possibility of dry residue being left on the surface of the stone therefore completely eliminating this problem.

Sometimes a good clean with a pressure washer and a stiff brush will help remove some light mortar staining left to dry on the surface of the paving, especially if a weaker mix of sand and cement has been used. When undertaking this be very careful not to damage the pointing by avoiding these areas and keeping the nozzle away from direct contact with the surface of the patio. 

The other way to avoid this is to use a premixed resin or cement based product such as Flowpoint from Instarmac. This product is reasonably easy to use and if undertaken correctly you will be left with a residue free installation. More information on this product can be found on the links below:

Flowpoint

If you find yourself in a situation where mortar stains have dried on your slabs and the use of a pressure washer and stiff brush are not removing the stains, it would be worth trying a cleaning product called ‘Rob Parkers Best Con Clean’. This product is formulated to clean mortar from natural stone however we advise that you are very careful if you are using this product on Black Limestone, other limestones, & Kandla Grey (Storm grey) sandstone, for more information please follow the link below:

Always read and follow the instructions before trying any cleaning products on natural stone or porcelain paving slabs, test first in an inconspicuous area with a small amount of the product and only continue if you are completely happy with the results.