Efflorescence on bricks: The causes, prevention and cure

We have probably all seen it! That nasty white powdery coating that spoils the look of brick buildings. A recent development of luxury home in Hertfordshire looked amazing when they were finished, but within a short space of time, the majority of these attractive red brick dwellings were white with efflorescence. So what is the cause of this phenomenon and what can be done to prevent or cure it?

Efflorescence is a crystaline, salty deposit that occurs on the surfaces of bricks, concrete and other masonry products. It is white, sometimes a brilliant white or an off white colour. Efflorescence has been a real bug bear of the building and construction industry for many years.

The formation of these salt deposits are not an inexplicable phenomena, they are simply water soluble salts that come from different sources to ruin the looks of otherwise beautiful buildings. In order for efflorescence to occur, there must be water present to dissolve and transport the salts to the brick surface. Water from the grounds surface can often be the cause of efflorescence. For this water to carry the salts to the surface of the brick, there must be channels or fissures for the water to migrate. When using a really dense brick, there is less chance of the salt laden water finding its way to the surface. Clearly, the open or more porous bricks suffer at the hands of this condition far nore than the dense brick products. When salt loaded water reaches the surface of the brick, air evaporates the water, leaving the salt behind. When the humidity is low, the water may evaporate before reaching the surface of the structure, leaving the salt deposit beneath the surface, and unseen. When the humidity is high, any water evaporation will be much slower and this allows more opportunity for efflorescence to form. Growths which project a quarter to half an inch below the surface of the brick has been reported in some areas of the country.

Owing to the fact that humidity has a definite effect on whether or not the salts appear on the surface of the bricks, it is extremely likely that efflorescence can be viewed as a seasonal problem. The intensity of efflorescence increases after very wet winters and tends to decrease in the spring time and by the time the weather has warmed up for the summer months, it has practically disappeared altogether. Unfortunately, this cycle of events may recur for months or possibly many years, but usually the intensity of the efflorescence will decrease in all but the most cases.

The efflorescing salts get carried to the surface of the brick by moisture and capillary action. The amount and character of the material deposited varies depending on climate, humidity and the porosity of the brick.

The actual problem of efflorescence, has been around for a very long time and engineers and academics have been studying the issue for many years. The studies all seem to agree that efflorescence originates from more than one source, and may be made up of more than one or two compounds.

Other salts such as chlorides and nitrates, and salts of vanadium, chromium and molybdenum are referred to in studies without giving the specific composition. Vanadium is said to produce a green coloured efflorescence on white or buff clay bricks, while other salts produce white or greyish deposits.

So what is the cause of efflorescence?

There are many sources for water soluble salts with some of these salts being more soluble than others. The movement of groundwater into the foundations of buildings and by capillary action into brickwork is very often the cause of efflorescence. Where soil conditions give evidence of water soluble sulfates, precautions should be taken to limit the passage of this water to the brickwork. Low water absorption is by far the best way to combat efflorescence. Carefully graded aggregates, a low water to cement ratio and good compaction and proper curing practices will produce a brick of a good density and with a low water absorption rate. Here at ET Clay Products, we strive to offer our customers a vast choice of quality bricks for every type of construction project.

Even raw materials such as sand and gravel may have been in contact with salt bearing water or soil, this can in turn transfer the salt to the finished brick product. It should be noted that these salts are not removed by a quick wash and therefore, this can be a possible, if not probable source for efflorescence. Most good quality aggregate plants in the United Kingdom are pretty careful about thoroughly washing their aggregate material so that any contribution made to efflorescence from their raw product is negligible.

Another potential source of soluble salts are clay products, such as house building bricks and facing bricks. Although a modern manufacturer such as ET Clay Products, ensure that the highly soluble salts are washed from the clay, and a barium salt such as barium carbonate is added to the clay product, to react with any calcium sulfate that remains. We know that when produced in this manner, our clay products show very little sign of efflorescence.

It is also a good idea to store the finished bricks wrapped and off the ground to prevent absorption of moisture. It has also been noted that the occurrence of efflorescence bears a relationship to the type of mortar used. With a particular type of brick and a certain mortar no efflorescence may occur, whereas, the same brick with different mortar may produce a wall heavily coated with white salt deposits. The appearances of sodium and potassium salts usually suggest Portland cement mortar as the origin. The use of low alkali cement in mortar and grout will help to keep efflorescence to a minimum, at least from this source.

Keep in mind that bricks and any other building materials that are in direct contact with the earth are potential sources for water soluble salts. This fact has been noticed by many manufacturers of building materials, and steps have been taken to reduce their presence as much as possible.

How to remove efflorescence

One method is to use water under pressure or one of a number of products available from stone dealers; another is muriatic acid followed by copious flushing with clean water. Acid applied to brick masonry, without previous wetting, may cause discoloration of the brick and may also eat into the mortar itself. Another method frequently used is the light sandblasting of the brick for removal of stubborn efflorescence. Allowing the surface of the brick to dry thoroughly and then using a stiff brush, prior to flushing with water, has helped prevent repenetration of the brick surface by the salt.

Various methods have been used in attempts to remove efflorescence from brick buildings. It has been found that when efflorescence is caused by soluble alkali salts, the salts will dissolve in water applied to the structure and migrate back into it. These salts would then reappear on the surface as the structure redried. It is now accepted that the best way to remove these soluble salts was to brush the surface thoroughly with a stiff brush. Water, however, has been satisfactory for removing efflorescence from the face of brick buildings. In fact, efflorescence has frequently been washed from the surface of brick buildings, if exposed to rain, over some period of time. If the coating is largely calcium carbonate or calcium sulfate, it adheres rather strongly and is difficult to remove by brushing alone. The practice developed in this case for brick and other masonry surfaces, has been to saturate the structure as thoroughly as possible with water, and then wash with diluted muriatic acid, followed immediately with an alkaline wash, then washed with water. The acid recommended is five parts hydrochloric to one hundred parts water, or twenty parts vinegar to one hundred parts water. The alkaline wash recommended is diluted household ammonia.

A great deal of care must be taken in applying acid to Portland cement products. The acid will attack, not only the calcium carbonate and calcium sulfate efflorescence, but also other calcium compounds to produce calcium salts such as calcium chloride. It is, therefore, very important to neutralise the acid before it can attack other compounds.

So if you would like to know more about efflorecence and how to avoid it, why not give us a call at ET Clay Products.

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