Efflorescence in Brick Pavers
When working on customer projects, Dr. Brick has received many questions from customers regarding the white, chalky substance found on the surface of brick pavers. So, we decided to add this article, which gives the complete definition of efflorescence. We hope this will answer any questions you may have. Feel free to contact us if you have any remaining questions.
The paver and patio pictures below are typical examples of the efflorescence appearance commonly found on brick paver hardscape products.
Efflorescence: What's this white stuff on my paving?
Efflorescence is seemingly endemic with all types of concrete paving and while its presence on a recently laid patio or driveway can disappoint the homeowner, they sometimes feel that the usual disclaimer from the manufacturers "efflorescence is a naturally occurring phenomenon¡... blah, blah, blah ... can accept no responsibility ... blah, blah, blah ... will disappear in time" is less than re-assuring and to some, it reads like a cop out, an excuse, a way of washing their hands of what is, after all, a visually distressing and disappointing problem. To be fair to manufacturers, they are stuck between a lump of concrete and a hard place. Try as they might, there's very little they can do to control the appearance of efflorescence, and what few technical fixes are available do tend to be employed by many of the better manufacturers. It's in their own interest to attempt to minimize the incidence of efflorescence, but even if they used every trick known, if they use efflorescence-reducing additives in the freshly mixed concrete, if they introduce steam to the curing chamber, or whatever other strategy is employed, there is no way they can guarantee that efflorescence will not be a problem with their products, because efflorescence is a naturally occurring problem and the chemistry involved is complex, involving a number of factors over which neither the manufacturer, the contractor, nor the homeowner has any control. So: what can be done to reduce the visual impact of efflorescence, or to speed its departure? There's a wealth of anecdotal advice out there, much of which is dubious, while some is downright dangerous, but there are some tried and tested 'tips of the trade' that are worth trying, even if they don't completely resolve the problem.
What is efflorescence?
Efflorescence is different things to different people. To the manufacturers, it's an insoluble problem; to the contractor, it's something else the client can blame on them; to the homeowner it's a white-ish discoloration that can appear to be like a powder or like the soapy scum seen on dirty bathwater, while to the chemist, it's most easily described as Calcium Carbonate with lesser quantities of other carbonate, sulphate, and chloride salts. The bulk of efflorescence seen with concrete paving is Calcium Carbonate, whereas for clay pavers, the main component is usually Sodium Chloride - table salt - along with sulphates and some carbonate. The remainder of this section focuses on Calcium Carbonate efflorescence observed on concrete products, as that is the most common form.
In simple terms, Calcium Carbonate is a by-product resulting from an interaction between the cement used to manufacture the paving and the natural environment, which includes the ground, the weather, and the atmosphere. The result is a deposit or 'salt' that appears on the surface of the paving. There's no single, definitive appearance - it is sometimes powdery, sometimes scummy: sometimes it's hazy and indistinct; sometimes it's sharp, crisp and obvious. Sometimes it covers large expanses or paving, sometimes it affects individual units, and sometimes it affects just half or two-thirds of a paving unit. It seems to affect dark hued pavings more than those of lighter tones, but the truth is that it's just more noticeable against a darker background.
However, it's always white-ish, although it might be a grey-white or a bluey-white, and it always spoils the looks and the coloring of the paving. It may seem to disappear when the paving is wet ¨C this is due to water turning the efflorescence salts temporarily transparent rather than actually removing them. Once the surface dries out, the efflorescence salts usually re-appears.
How does it disappear?
As mentioned in the chemistry lesson above, the white bloom is gradually converted to a soluble compound that is simply washed away by the weather and/or a hosepipe. However, there are other factors that act to reduce or remove the visual impact of efflorescence.
The tiny pores and voids within the concrete matrix through which the soluble Calcium Hydroxide is transported eventually become plugged with deposits of the insoluble Calcium Carbonate. This effectively blocks the escape route for the Calcium Hydroxide and 'locks in' any further reactions, forcing them to take place below the surface and, conveniently for us, out of sight.
Simply walking over or driving on the paving will abrade the deposit, wearing it away and reducing the quantity visible on the surface.
Although we know that rain can dissolve and wash away the soluble products of efflorescence, it can also wash away some of the insoluble material, in the same way that sand or other detritus can be washed from a surface. Other weather phenomena, such as wind, snow, hail, etc., can also accelerate the removal of both soluble and insoluble matter. Rain that is slightly acidic is better able to dissolve the deposited salts, and so the problem may disappear sooner in urban areas than would be the case in rural locations.
How long will it last?
This is the tricky question. No-one can say how long any incidence of efflorescence will last. It might be a few weeks; it might be a couple or three months; it &could be a year or two. There are so many factors affecting its generation and appearance, and its disappearance that an educated guess is the best we can manage. We know that certain conditions have an effect: damp, shady sites can be more adversely affected than open, sunny sites, and, for some reason, the phenomenon always seems worst when the daffodils are out, which must be linked to climatic and ground conditions in some way, but no-one is really sure how.
However, such an answer doesn't do a lot to dispel the legitimate concerns of the homeowner. They've handed over a big wedge of money for a patio or driveway and it looks, to be brutally frank, bloody awful. Judging from the feedback received at the Paving expert website, most cases of efflorescence become noticeable 3-6 weeks after laying is completed and then last for 3-6 months before gradually disappearing over a period of 3-6 months. It seems that most people never notice it coming ¨C it just 'appeared' overnight - and most don't notice its departure: one day, they realized that it's no longer there and they'd almost forgotten all about it.
These figures are averages: don't complain to me if your's lasts for 2 years, and don't come crowing if it's been and gone and done it in a fortnight. That's the nature of the beast: it lasts as long as it does and it goes when it's done.
The following is an excerpt from a comprehensive article on the subject of efflorescence. The complete text can be found at www.pavingexpert.com
Can it be shifted more quickly?
Obviously, manufacturers and suppliers of the various wonder treatments have a vested interest in declaring their jollop to be the best, the fastest, the most effective, but how can that be proved with something so apparently random? There's no doubt that some of the proprietary products do remove the visible salts from the surface of the paving, but it is a temporary fix ¨C the problem is very, very likely to return.
Any 'chemical' treatment needs to be considered very carefully and tested on a discreet area before daubing it all over the rest of the paving. Many of these products are based on a mix of detergents and acids that 'eat' or 'dissolve' the insoluble carbonate and allow them to be washed away. However, some acids may also react adversely with pigments used to color concretes and can result in alarming color changes. Further, they can actually exacerbate the problem by un-plugging the blocked capillaries and micro-pores which then allows the Calcium Hydroxide to find its way to the surface once again. Although stone products tend not to be affected by efflorescence, they may be used in conjunction with or adjacent to areas of concrete or clay paving, and acid-based products may cause dramatic discoloration or damage to the stone.
A non-chemical strategy involves regular brushing and rinsing with clean water. This helps remove both soluble and insoluble products of efflorescence and may actually accelerate the eventual permanent disappearance of the deposits. There have been suggestions that a few drops of wash-up liquid added to each bucket of water can also help.
As more and more of us acquire power washers, these are increasingly being used in the battle against efflorescence, but it's uncertain whether they help or hinder. There's no doubt that they can and do remove some of the deposits, but they can also damage the surface of the paving, especially when used regularly on wet cast flags, and there's a suspicion that the powerful jet of water may un-plug the pores within the paving. Their use is probably worth considering once or twice per season where deposits are heavy, as they can make a dramatic improvement, albeit temporary, but regular use is probably detrimental.
Mechanical methods include sand-, grit- or shot-blasting to remove the efflorescence deposits, along with a thin layer from the surface of the paving. This strategy is generally unsuitable for residential paving as it degrades the surface, which is, from the viewpoint of the homeowner, the most important part, but the strategy is used on some commercial projects and on troubled areas of in-situ concrete.
What about sealants?
There's a train of thought that runs something like this: The efflorescence is unsightly, but it is less noticeable, or disappears completely, when wet ... so, if a sealant was used to give the paving a permanent wet look that should eliminate the problem. The flaw in this argument is that ¡°wet-look¡± is not the same as ¡°wet¡±.
There's a whole range of different sealants, but for the purposes of this discussion, they can be divided into two camps: those that form a 'film' on the surface of the paving, and those that penetrate and form a more considerable barrier extending several millimeters into the paving. Those sealants in the 'film' camp are generally ineffective against efflorescence as the process continues and the carbonate material is deposited beneath the thin layer of sealant. The penetrative types tend to be more successful because they block the pores of the paving near the surface, thereby limiting ingress of water and carbon dioxide, and egress of calcium carbonate, which often remains trapped within the paving unit.
However, the accepted wisdom is that it is much better to delay application of any sealant until efflorescence has dissipated. It's deemed better to allow the process to exhaust itself and therefore be fairly certain that most or all of the unsightly deposits are gone before spending money on a sealant. After all, a few weeks or months of what is relatively minor visual inconvenience is preferable to years and years of being faced with 'preserved' deposits, of efflorescence trapped and protected beneath a sealant.
With block paving and other flexible segmental paving that uses sand joints, it's never a good idea to seal a pavement too early in its life as there needs to be a period of joint stabilization, time for the jointing sand to settle and self-seal before 'fixing' it with a sealant of some sort.
When will it ever end?
As long as there is 'free' Calcium Oxide in the system, whether that is within the paving units themselves or the bedding, efflorescence may continue. However, it may be taking place on such a relatively small scale that it's hardly noticeable, and it may seem the problem has 'cleared up'. Eventually, the supply of free Calcium Oxide will fizzle out and the efflorescence will be at an end, but hopefully, the visible effects will have all but disappeared long before then.
How can efflorescence be avoided?
The homeowner is powerless. There's nothing they can do that will have much of an impact on whether or not efflorescence becomes a problem. They are limited to dealing with the problem if and when it occurs. However, the manufacturers and the installation contractors can take steps to minimize the potential for problems, but there is no way they can eliminate it completely.
As it says in all the manufacturers' brochures, efflorescence is a natural phenomenon and is best left to resolve itself. It's not pretty but it doesn't actually do any long-term harm to the paving and in the vast majority of cases it will be over and done with in a few months. If it's really annoying you, a stiff brush, clean water, and elbow grease is the best option. Proprietary cleaners and 'efflorescence removers' are, at best, temporary fixes but can improve the appearance in the short-term. Sealants are best left until the problem has cleared up. Complaining to suppliers, manufacturers or contractors is unlikely to achieve anything. The better companies and tradesmen do what they can to minimize the problem but it really is impossible to eliminate. If you think you've found a way to resolve the problem, either to clear it up once and for all, or to prevent it happening in the first place, you should contact me immediately and I'll tell you how we can share the fortune we'll make!