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WHAT IS EFFLORESCENCE?
Efflorescence is a visual effect which can appear on the surface of a concrete product in the form of a white deposit. The nature of this deposit can vary from a fluffy powdery substance, a harder, less distinct hazy bloom or a scum-like deposit.
With concrete paving these deposits are inorganic salts, predominantly Calcium Carbonate, although other sulphate and chloride salts may be present in lesser quantities. The effect can be random, affecting very few blocks or multiple areas of the surface.
There are multiple variables which will determine whether efflorescence will ever be seen or not and we as manufacturers take all possible measures to minimise the probability of efflorescence occurring. However, efflorescence is extremely difficult to predict and to completely avoid as these soluble salts are present in the natural aggregates and cement used in the manufacture of the concrete. It is therefore impossible for any concrete product manufacturer whose products contain cement and lime to completely guarantee efflorescence-free products.
Having invested in a nice new driveway or patio, the appearance of efflorescence is without doubt a worrying, annoying and disappointing effect for the homeowner and we as manufacturers strive to take every measure possible to avoid its occurrence. The good news is that efflorescence is completely harmless, not detrimental to the blocks, can be removed and will gradually disappear over time.
For further information please take a look at our Literature section for our Efflorescence Block Paving Factsheet.
All concrete blocks and pavers contain natural substances containing an amount of soluble salts to a lesser or greater degree, depending on the block type and the origin of the raw materials used in their manufacture. This varies from plant to plant due to sourcing local supplies.
Moisture from the manufacturing process or from rain will interact with these soluble salts and will migrate to the surface due to the fact that all concrete products, even our strong and dense pavers are porous to some extent. The Carbon Dioxide in the atmosphere will react with these soluble salts (e.g. Calcium Hydroxide will turn into the insoluble Calcium Carbonate) and as the moisture evaporates the characteristic white, crystalline efflorescence will be left behind.
The mechanism for efflorescence begins as soon as the blocks are manufactured and will continue to the point that the soluble salts are used up within the block and the efflorescence will gradually fade. As the insoluble Carbonate salts are exposed to further Carbon Dioxide in the atmosphere, they will slowly convert into soluble Hydrogen Carbonate substances and will wash away and dissipate naturally.
Efflorescence can come and go over a period of a few weeks but can take many months in some cases. Local conditions and climate play a part; damp shaded areas tend to be more prone to efflorescence than drier sunnier areas and efflorescence can be more pronounced during springtime following a wet winter.
There are a number of approaches one can take to deal with efflorescence should it occur. Dealing with it promptly once it is seen will quicken up the process by which the soluble salts present within the block and surrounding materials are exhausted and efflorescence will disappear permanently.
1. Leave it to naturally fade
As described, simply allowing the efflorescence to naturally fade away and vanish is the one guaranteed approach. This is however a long-term approach and leaves the homeowner with a less than perfect driveway or patio for a longer period than desired.
2. Regular dry brushing
This is our preferred, recommended remedial method and can help speed up the natural and permanent tailing off of the occurrence of efflorescence.
Using a medium stiff-bristled brush (not a wire brush - this would damage the surface!), dry scrub the affected areas and sweep away as much from the whole surface as possible to prevent it from simply re-dissolving when it gets wet again.
Do not wet scrub as this will simply redistribute the dissolved salts across the surface only to reappear again when dry. Once the dry visible deposits have been scrubbed away and the area thoroughly swept with a yard brush, the paving can be hosed down to wash away any dusty deposits and soluble Hydrogen Carbonate substances.
This process will need to be repeated regularly initially and may indeed result in efflorescence seeming to get worse. This is however a good sign that the salts are being brought to the surface and is helping to speed up the natural exhaustion of efflorescence-causing compounds in the blocks.
3. Chemical treatments
There are many products available claiming to deal with efflorescence which are usually based on detergents or acids. Whilst these products may well be effective in removing the efflorescence initially, the salts will continue to naturally migrate to the surface and form new deposits. The chemicals in these treatments may even damage the surface of the block or affect the colour pigmentation and for this reason we do not recommend the use of strong chemical treatments and advocate the dry brushing method.
4. Power washing
Although power washers will remove a lot of the visible efflorescence and are excellent at removing lichen and weeds for seasonal cleaning, much of the efflorescence will be re-dissolved rather than being completely removed and therefore provides a temporary fix as the salts will dry out and the deposit reappear. Furthermore, very regular use of a vigorous and powerful jet can actually damage the surface of the paver and exacerbate the problem as moisture will ingress further into the surface of the block. We recommend the careful use of a power washer only two or three times per year for normal cleaning down and maintenance or if deposits are particularly heavy.
Whilst we as manufacturers take every possible measure to minimise the possibility of efflorescence occurring there remains the stark fact that the natural and unavoidable constituents of the product can cause efflorescence to a lesser or greater extent and there is no way to predict this.
Unfortunately, there is little that can be done to totally prevent efflorescence occurring and the only approach is to deal with it once it appears as per the dry brushing method described above. This will quicken the process to the point it permanently goes away. As manufacturers we cannot be held liable for efflorescence appearing since it is a natural and harmless effect, completely non-detrimental to the product and will disappear naturally.
Sealants are a useful and proven method to preserve the appearance of paving long-term and provide added resistance to staining and spills. However, we do not recommend the use of applying sealants to specifically deal with efflorescence. A surface sealant cannot prevent efflorescence and will simply trap it leading to the unfortunate situation where the efflorescence is visible but cannot be removed due to the sealant and therefore cannot naturally fade and dissipate!
If a sealant is desired, it should never be applied to a newly-laid surface! Sealing should not be considered until long after any efflorescence has been completely exhausted and the paving, sub-bases and joints have had time to completely settle.
In common with our other concrete products made with a high cement content our products may exhibit the temporary surface phenomenon of efflorescence. This may appear as a milky white stain on the face of the product or the appearance of the paver may be such that the colour has faded. This is in no way detrimental to the performance of the product and responsibility cannot be accepted for its occurrence.
Thomas Armstrong (Concrete Blocks) Ltd
Part of the Thomas Armstrong Group
T: 01900 68211
F: 01900 602672