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Efflorescence
Efflorescence, have you seen this white stranger?
Ever wonder seeing some sudden white fuzzy stuff in the surface of your structure like wall, brick, ceiling and uttering yourself “from where is this white stranger?” Well, if you experienced so, this post is for you. This fuzzy stuff is called ‘efflorescence’. The word ‘efflorescence’ means ‘To flower out’ in French. But here, the case is ‘flowering out’ of some salt from your structure. This is a typical and most frequent problem that contractors face especially in case of colored concrete and bricks.
Basically efflorescence is a deposition of crystalline salt inside or outside of the surface. If you see any efflorescence then there must be a water contact or water presence in the concrete. It is caused when water with any soluble salts come to the surface through capillary action and then vaporize. While vaporizing, it leaves the salt and basically what we see as efflorescence, is this leftover salt. This can happen for various reasons like moist condition, rain, dew or any external or internal water. Casting the concrete with salty water can be another reason behind this. Let’s look for another chemical mechanism. Sometimes by hydration reaction, calcium hydroxide or lime is formed from Portland cement which is transported by water to the surface. Then it reacts with carbon di oxide from air and produce calcium carbonate and at the end can cause efflorescence. That’s why any material having Portland cement can cause efflorescence. Besides, hydroxides or sulfates of potassium or sodium can create efflorescence which can come from cement, water, aggregate or even admixtures. They form faster efflorescence than calcium. Now there come’s an important question, is this a serious problem? Well, in simple words, efflorescence isn’t very serious problem, but it can create some severe problem if ignored over the time. First of all, there is an esthetic problem if efflorescence occurs. As efflorescence is a sign of excessive moisture attack on structure, so not addressing the problem can lead some unpleasant surprise like structural damage or mould formation. Sometimes salts inside the structure react with the other structural materials and can damage gradually.
Protecting your structures:
To protect from efflorescence, we have to know how it comes. By now, we know, three cases must be occurred for forming efflorescence. They are-
Water must present in the mortar bed.
Soluble salt must present. These salt can come from manufacturing process of Portland cement.
Some type of transportation media like gravity force or anything that bring the salt to the surface.
So, in order to prevent efflorescence, we must prevent these three causes. Sometimes after eliminating these causes Some best options are here: Site surface drainage, concrete not exceeding 4” slump, well graded mix, well consolidated, welly cured-- these are some factors which can reduce amount of bleed water and pores in which moisture moves, and thus reduce efflorescence significantly. Curing is also an important factor here. We know moisture moves more slowly in denser concrete. When concrete is kept cured or moist for longer period like a few days, more capillaries and pores fill partially or fully, hence, form a denser concrete and reduce efflorescence. Use of an epoxy setting material may also help reduce efflorescence. Besides, admixtures containing aqueous-based calcium stearate dispersion (CSD) are often added. Normally, sand is first kept into the mixer, Oil-based primary anti-efflorescence admixture is then added with constant mixing that allows the oil to coat the sand which prevent further moist absorption.
How will you remove this?
The typical way of efflorescence removal is brushing and sandblasting. It works but most often, along with the efflorescence, sand erodes the bricks and mortar with its abrasive force which can damage the structure as well as beauty. Another alternative solution is using chemical cleaner. Normally presoaking and post washing is required with clean water. Presoaking is done to saturate the wall or the structure before using chemical solution. Presoaking limits the pores or capillary length of the structure with water. This is important because most of the chemicals are acidic in nature and can damage the surface. As presoaking limits the capillary length, acid cannot reach depth to structure. After chemical cleaning, again washing with clean water is also required. And last of all, it is safe to approach non acidic cleaner first because some surface can be sensitive to acid. Starting can be with a stiff brush. It’s best to wear a respirator, safety glasses and gloves. Acidic cleaner is dangerous to people as a well the surface, so it is always safe to entrust the job to a specialized contractor. Because it is always better safe than sorry!