Exterior paving – common issues when using natural stone in outdoor areas
Using natural stone as a building material in outdoor areas transformed the idea of durability from a couple of thousand years ago. From ancient Egyptian pyramids to Roman pavings, from Michelangelo statues to Taj Mahal, the use of natural stone has expanded on an increasing scale and these day we cannot imagine an ecological and sustainable building without natural stone.
Ootdoor use for natural stone include, then and now, exterior paving and flooring. Exterior paving include terrace paving, pool coping around swimming pools and stairs. These are made from rectangular or square shaped stone tiles. Exterior pavings are usually made of cobblestone or flagstone. PIATRAONLINE product range for terrace paving starts from square tiles such as Kavala Marble, 2 cm thickness up to rectangular such as Padang Dark Granite, 2.5 cm thickness.
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What causes efflorescence?
For both terrace and swimming pool, but also any exterior paving (with small joints or without joints) there is risk of efflorescence. This is produced by water penetrating the underlay, while collecting and transporting minerals and salts encountered during its migration across the mortar bed or the adhesive beneath the cladding, or even across the soil serving as support for the cladding. When contaminated water reaches the surface, it will evaporate leaving behind minerals and salts. Residues left after evaporation are those white traces from the surface called efflorescence.
Developed efflorescence indicate substrate moisture, thus making water cleaning of surfaces uselless. Initial phase includes dissolving white powder in water, making it look like wiped off from the surface, yet coming back as soon as water is evaporated. You can solve this efflorescence by drying the moisture source from the interior. For avoiding moisture, cladding is recommended on a completely dry surface (cured). Also for avoiding the humidity effects in risky areas (bathroom, kitchen or basement) surface sealing is recommended, followed by cladding. In humidity areas are recommended solutions for blocking water access to the surface. Sealing surfaces cladded with natural stone will not stop efflorescence but it can slow it down. Efflorescenses will occur when failing to comply with the required drying time after sealing, thus moistening surfaces before drying.
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For non-sealed surfaces, efflorescence develop on regular basis. A confusion generating situation happens with rainwater evaporation, which produces sometimes a whitish residue on natural stone surfaces. When surfaces are sealed, residues are easily removed because are not the result of moisture deep within surface. Water will penetrate easily the untreated surfaces, making its way beneath the surface and generating phenomenon of efflorescence in time the. Therefore, it is mandatory to seal exterior surfaces.
How to remove efflorescence (white stains)?
If surface does not contain limestone (marble, travertine, limestone) or sandstone with high iron content, then wash surface with an acid-based detergent such as LTP Grout Stain Remover. On acid sensitive surfaces, simply use water or an over diluted solution of LTP Grout Stain Remover, tested previously on a small size, less visible surface. Efflorescence will diminish and can be removed over time, as long as surface is properly sealed.
How to choose a stone waterproofing?
It is vital to use a sealing solution that allows surface to breath and as a result, evaporation of water that generated moisture under the cladding in the first place. Here are a couple of solutions from LTP – UK:
LTP Stone Oil (color enhancement for dark color stones) as an oil-based sealer, it is recommended for honed, flamed, tumbled, bush hammered, splitface or brushed finished stones.
LTP Mattstone H2O is a water-based sealer, with excellent results in surface sealing, regardless of finish.
LTP Mattstone is the solvent-based option of the previous sealer, used for unpolished finish stones.
LTP MPG is a powerful sealer, with fine results for polished finish surface.
Two final tips:
Avoid mopping the sealer over exterior surfaces due to risk of over-dosage. The best option is spraying the solution. As a result, you will avoid thick coats that make drying process difficult.
Obviously, the above information is provided only as a general guide, without any warranty. Particular situations might require alternative approach. When in doubt, always test solution on a small size, less visible area, before applying over the entire surface.
For expert advice get in touch with us by email at firstname.lastname@example.org or by phone at +40.318.222.333!
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