Typically, any patches that appear on the surface of natural stone paving once laid is nothing to be concerned about and can occur depending on a handful of variables.
When looking at your new patio, it’s often easy to forget that the stone you’ve just laid has existed for thousands of years and was around long before our lifetimes! Any patches or marks which appear on the stone after laying will simply be due to the stone adjusting to its new environment and will typically be very simple to solve with a little patience. The type of patches you see will depend on the laying method, the mineral content of the stone, any sealing or aftercare products and the environment.
Remember: Any issues with the stone itself, such as the size or thickness of the slabs, will always be evident before laying. You should never use any slabs which feature any suspected faults and should raise this with your supplier for further advice.
For some in-depth advice on laying paving slabs and tips on how to prevent any problems, see our Installation Guide.
Efflorescence is a natural process where salts are drawn up through the slabs and leave chalky looking white residue on the surface.
When the stone drys out it will suck in moisture from the wet mortar beneath. This moisture will make its way up through the stone, carrying particles of cement from the bed, as well as iron and minerals from within the stone, up to the surface. These are later deposited on the surface of the slab as a white, chalky substance.
This efflorescence is not a fault in the stone and is a natural process that can vary in intensity from slab to slab and will also depend on the mineral content of the stone.
If you see efflorescence on your slabs, allow a few weeks for the minerals and salts to work their way out of the stone, sweeping the chalky residue away regularly until it subsides. There are also specialist products available that will aid with the removal of efflorescence such as LTP Cement, Grout & Salt Residue Remover.
This is one of the reasons why it is so important to be sure that your slabs are primed properly with a priming slurry and that the whole of the underside of the slab is coated and in full contact with the bed with no voids. However, efflorescence is nothing to worry about and can easily be removed with some patience.
Picture Framing & Patches
Patches around the edges of the slabs are referred to as ‘Picture Framing’ and are due to moisture being drawn into the slabs from the jointing compound or mortar base. These patches won’t typically remain permanently.
On a warm and dry day, this picture framing will usually dry out but can appear again in wet or humid conditions as more moisture is drawn back into the slab. The natural porosity of the stone will determine the extent of the patches and will vary from slab to slab.
If the problem doesn’t subside after a few weeks, we recommend the LTP Cement, Grout & Salt Residue Remover. However, it’s important to be patient with this before rushing into treating the slabs.
Uneven application of a sealing product can also cause patches to appear, so it’s important to take your time when applying any sealant to the stone and follow the manufacturer’s instructions carefully.
LTP have some further advice on patches that occur within your paving after laying which you can read HERE.
Natural stone contains iron which can be drawn from within the slabs to the surface and appear as orange or brown marks.
Mineral oxidation is a natural occurrence and won’t affect the performance of your stone. The visible effects of this will naturally dissipate over time and there are plenty of products available which will help you to remove the marks if you’d like to speed up the process.
If you notice this on your slabs before laying, it’s important to remove the oxidation before laying your slabs.
Non-natural oxidation can appear on your paving from things such as garden furniture and vehicles depositing rust onto the surface of the slabs, as well as any spillages with high acid content. Anything containing acid or ferric sulphate will cause the natural iron particles to be drawn up through the stone and deposited on the surface, leaving an orange coloured stain.
For marks such as this, we recommend LTP’s Rust Stain Remover.
Spot Bedding, Ring Bedding, Dot & Dab Method or Five Dotting Techniques will bring out some unsightly reflective staining on the slabs where liquid and minerals are pulled through the surface unevenly.
These laying methods leave gaps beneath the slab where the stone is not in contact with the bed and can also cause some issues with the stability of the slabs. Methods like this are not recommended within the landscaping industry and removing the marks entirely is almost impossible without taking up the affected slabs. If you’re unsure of the laying method used, tap across the surface of the slabs with the wooden end of a hammer and listen for a hollow sound beneath any part of the paver.
Depending on the extent of the problem, the LTP Cement, Grout & Salt Residue Remover may help to make the marks less visible and we would recommend contacting LTP directly for advice before going ahead with using the product.
Most types of patches you will see listed above are completely normal and are simply due to how the stone draws moisture from its new bed. These won’t always appear and most are will subside or can be treated easily.
It’s important to remember that if you do see any of the above, these are not defects with the slabs. As a natural product, it can’t be pre-determined whether you are likely to see any of these as they will vary due to the mineral content of the stone, laying method and any products used on the slabs. Any issues with the stone itself such as breakages or incorrectly cut slabs will always be evident before use and you should report this to your supplier before using the product.
We hope that this helps you to identify what you are seeing in your stone and how to rectify it. As always, if you are unsure of anything, always seek further advice. Any good professional landscaper will be happy to help identify any patches or marks which appear and all the information on this page should help you to identify the most common issues. We’ve also listed some industry experts below who have plenty of experience identifying such things, should you need to reach out to them!