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Common Problems when Fixing Stone Outside

Published 20 May 2015


Stone patios and white blooms- Efflorescence


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You’ve seen the magazine pictures: Designer patio’s decked out with stylish garden furniture, blue skies and a perfect sandstone/limestone  floor tiles… Yes all this is perfectly feasible but for a flawless floor you rely on that blue sky..infact from our experience at least 3 days of blue sky.     The most important factor when deciding  to seal any stone outside is the British Weather.. unless 3 dry days and nights (no rain…no dew) can be guaranteed then there is a strong chance your floor will not look like the one in the picture.

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stone outside blog 3 A much more common scenario is a phone call to the supplier of the stone asking why the tiles and or grouting  have gone white overnight.

This is not a insurmountable problem as the bloom can easily be removed and in all the cases we have seen the tiles settle down over a period of time.

However, to save unnecessary worry it might be useful to learn why this issue can arise and how to resolve it.

All stones located outdoors can be susceptible to a condition known as efflorescence. It is caused by water moving through the substrate of a material collecting and carrying minerals and salts found in the mortar bed, grout, soil or the stone itself.

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When the impure water reaches the surface  and evaporates, the minerals and salts will be left behind., these form those white marks or efflorescence, seen on the surface. Whilst this phenonemom is more common on unsealed surfaces it can also occur on sealed surfaces especially if the stone becomes wet before the sealer has fully cured, which can take up to three dry days.

Ironically once the stone is sealed this efflorescence can seem enhanced as the sealed surface traps the rain water on the surface which also evaporates leaving a white residue especially in hard water areas..  However no pain no gain.

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It is important to go through this scenario and run the risk of a white bloom on the surface as it is only by fully sealing stone that will prevent water percolating through the stone and triggering the efflorescence cycle once again.

How to remove efflorescence:

If the surface is not a Limestone or a Sandstone containing high iron content then wash the surface with an acid based cleaner such as LTP Grout Stain Remover On acid sensitive surfaces then simply use water or a very mild solution of Grout stain remover (trial in a small area first). The efflorescence will fade and can be removed over time and provided the surface is properly sealed it will cease over a period of a few months.

What is the best sealer to use:

It is vital to use a breathable sealer that allows the transition of moisture from underneath, examples include

LTP Stone Oil (offers colour enhancement for Dark Stones)

In our experience the best sealer to use for external use in that it seems to trigger fewer cases of efflorescence is our waterbased LTP Mattstone H20 and External Stone Sealer

One final bit of advice:

Do not over apply the sealer as the second cause of efflorescence , after the British weather , is too much sealer on the surface. As a rule of thumb it is best to apply roughly half as much sealer as would be appropriate for interior use.

Still unsure? Try our new product guide to help select the correct products.

Please note that this information is offered as general guidance only and without guarantee. Your specific circumstances may need an alternative approach. In case of doubt, any process should be tried out in an inconspicuous area before general application.