One inherent problem when using masonry and concrete products around the home is efflorescence and no we are not referring to a fizzy drink!
From a scientific standpoint, there are a few different types of efflorescence and the one most likely to cause worry around the home is primary efflorescence.
Efflorescence is the loss of water of crystallisation from a hydrated salt to the atmosphere on exposure to air. Sounds complex right? Essentially, around the home or job site, efflorescence typically occurs during the initial cure of a cementitious product and mostly will present in masonry products, bricks, blocks and pavers.
When pavers are first laid, a block or brick wall is built there is often latent water present in the product. This water may be present due to the manufacturing process, product sweating from long-term packaging, water being added to the product during or after the installation or site moisture. Concrete and masonry products, being porous, will naturally absorb surrounding moisture as they are highly porous materials.
When water moves through a brick, block or paver, quite often drawn to the surface by heat, it brings with it salts that are not commonly bound as part of the cement product. As the water evaporates, it leaves the salt behind, which forms a white crystal-like deposit.
In some case’s, particularly on vertical brickwork, this deposit can be brushed away with no further treatment required. But on many horizontal surfaces like pavers, particularly dark coloured products a white stain will remain and need specialty cleaning products to rejuvenate.
One of the most common complaints we hear is regarding a freshly laid charcoal (or similarly dark coloured paver) developing white marks or discolouring over the first few weeks and more often than not it is the occurrence of efflorescence.
How Efflorescence occurs in Pavers
Efflorescence can be cause by moisture and soluble salts in either the paver itself or the surrounding environment.
As mentioned previously, efflorescence is caused by the presence of water in masonry products and as explained, masonry and concrete products are manufactured using water and also love to absorb and hold that water! So naturally, your fresh off the production line pavers will have latent moisture present.
In the case where moisture is present in the product, or water was present before, during or after the installation process (rain, wet sand, hosing to clean) occasionally efflorescence can occur. In these cases, the hot sun will begin to dry them out once they have been laid. This could happen as quickly as a few days if laid in the middle of summer or over a few months if in a shaded courtyard during the winter months. Once the water moves through the paver and hits the surface, the sun will evaporate the water leaving the salt crystal.
Efflorescence in pavers may also be caused by other external influences, such as your laying technique, other products used on the job (like sand) or even the presence of a swimming pool (salt in the water). When a masonry paver is direct stuck to a concrete slab using mortar adhesive or laid on a wet bed, the “drier” paver will suck up the moisture present below beginning the cycle mentioned above and bringing with it salts present in the wet adhesives.
Similarly, if you lay your pavers on inferior unwashed sands, Crusher Dust or Cracker Dust you may also experience salt absorption when moisture is present. Most bedding sand products are of a river origin and should be cyclone washed before arriving in a landscape yard, if not there may be soluble salts present. Likewise, Crusher Dust or Cracker Dust, being a crushed rock is full of minerals including salt which again can cause long term problems.
We recommend all masonry and clay pavers be laid on a layer of clean washed bedding sand (30mm) over a firmly compact layer of CBR45 (min) Roadbase (100mm). This will ensure none or minimal efflorescence will be caused by the external materials.
How to Minimise Efflorescence Occurrence
Most cases of efflorescence will naturally take care of themselves, as your pavers will eventually dry out and the salt deposits that may be present will become depleted. Make sure you follow the manufactures recommended laying technique (which in most cases will match the above process using sand and roadbase). Lastly, seal your pavers! Sealing your pavers essentially blocks out any chance of new water entering through the top and starting the drying process over. Although, we do recommend waiting a few weeks after laying to allow your pavers the chance to fully dry-out. You don’t want to seal the efflorescence in!
One thing to remember is, although unsightly, efflorescence is treatable! If it happens to you, allow your pavers to dry out fully, giving every chance to bring as much efflorescence to the surface as possible. Then treat the area using a specialist product such as Anti-Eff from Environex. Anti-Eft is a special formulation utilising the reactive quality between acid and mineral deposits. Make sure you follow the recommended concentration, allow to dry out once again and treat the entire area with a high quality penetrating solvent sealer. This will lock out the moisture and ensure your pavers stay in good nick for longer!