^{Salt contamination: what is it? what causes it? what to do?}‍‍

Moisture activates salts in various building materials; these include brick, concrete, stone and plaster. The source of the salt contamination can also be environmental; for example, air borne salt in coastal areas.

It is the salt that causes the damage, not the moisture. An important thing to note is removing the source of the dampness will not in itself fix the salt damage in the long term, as the salts will continue to form.  

Therefore, dampness and salt contamination need to be thought of as two separate things to address.

Many contractors will fix the dampness source but do nothing to address the salt reoccurring. I often see cases where the “dampness fix” does nothing to prevent the salt damage re occurring. In some cases, “the fix" actually makes the salt damage worse. For example, scraping done prior to waterproofing by many dodgy workers, results in a "band-aid repair".

When we refer to salts in buildings there are a few different types. All have one thing in common; they all have Cations which are positive charged ions+ and Anions which are negatively charged ions. Moisture increases the reactions between these irons and produces salt deposits, which then track to the surface.

The two most common forms of salt contamination we come across are Efflorescence and Sub Efflorescence.

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Efflorescence

Efflorescence is where salt crystals forms on a wall or tiles without damaging the surface. Common examples are white stains on new tiles and face brickwork.

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Sub Efflorescence

Sub efflorescence is where the salt crystals form just below the surface of the wall. They cause damage to the surface including delamination (think flaking where the surface pulls off). This is very common, especially brick whether rendered, face brick or sandstone.

The most common causes of salt blisters I see are rising damp –moisture from below rising up through the masonry, where there are no damp courses, or the damp course has broken. This is bad because water goes up and through the wall to make it wet, activating salts that bugger up the plaster and lateral damp. Lateral damp is usually caused by moisture behind the wall penetrating through to the inside surface, typically in areas below ground level.

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What causes Efflorescence?‍

In the case of efflorescence on tiles, the most common cause is a poor-quality sand cement bed under the tiles. Usually this is the result of two issues: lack of fall in the structure under the tile bed and a weak porous tile bed. Both are the result of poor building practice. If there is no fall in the substrate, water tends to pond under and keep the tile bed saturated. This causes salts to form and track to the surface, leaving salt deposits.

The second issue is a tile bed that has no water resistance. The tile bed should always have a water proofing additive in the mix and a membrane such as a water-based epoxy applied over the bed once it is cured.

The most common additive used in the tile bed is a product call Efflock. This prevents water from soaking into the tile bed, therefore no salts are activated. This product is expensive; hence many contractors omit its use.

What causes Sub Efflorescence?

Apart from airborne salts in coastal areas, the most common causes of sub efflorescence are rising damp and lateral damp.

This dampness activates salts. The salts can be from the soil under in the case of rising damp on ground floor walls or within the materials.

On older buildings the sand used in the mortar mixes often contained a lot of salt.

What to do about Efflorescence salt contamination?

The ‘fix’ varies depending on the location, materials and the cause of the contamination. Usually when we come across efflorescence it is combined with leaks, water ponding in tile beds, cracking and other issues. As a start, existing tiles, cement bed and waterproofing need to be demolished to the point of bare concrete or its subbase for a redo to fix the leaks.

This is an example of a poorly constructed balcony. There is a porous weak tile bed, negative falls and a host of other issues. In time these balconies will need to be redone.

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What to do about Sub Efflorescence salt contamination? "Rising damp"

On cement rendered or lime rendered walls, the affected render needs to be removed to expose bare brickwork. In most situations we remove the render approximately 300-400 mm above the highest salt blister and or high moisture reading.

In most cases we do not need to desalinate the brickwork. Where the damage is extensive, we apply a poultice to draw out the salt. We use a product called Cocoon which is made by a Sydney company, Westok.

Once the render is removed; a new damp course is installed at a suitable level, usually a brick course above floor level. In certain locations we will also install vertical damp courses.

The method we use is Westok chemical injection: 10mm holes are drilled in the brickwork or stone. The chemical is a silane solution. This is injected under low pressure and soaks into the brick or stone. This photo shows an injected damp course with vertical returns each end on a current project

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Once the injected material has cured for 2-5 days, the walls are rendered using Westok Salt Retarder diluted in water: GP cement and sharp or washed sand. If the renderer adds anything else to the mix, such as plaster master or renderers clay, it will not work, and the salt contamination will likely reoccur. I see this often, renderers replacing salt affected render with standard render... it just doesn’t work. 

The salt retardant render can be left plain or a coated with standard set plaster. After about 3 weeks the walls can be painted using standard paint systems.

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Sandstone salt damage

This is a very brief overview, and every project is different. I highly recommend only using specialists in this field. It is common to see fixes that compromise the stonework and increase the damage.

In some cases, we drill test holes to gather samples that are tested to determine the salt content. It is critical that any mortars used are suitable and especially weaker than the sandstone.

The two main sources of sandstone salt damage I see are airborne and rising damp. Airborne salt is usually in coastal areas. Rising damp is usually seen in sandstone foundations that draw salt up from the ground. In both cases we desalinate the stone. A poultice is used to draw salt from the stonework. We use Cocoon from a Sydney company Westok. Usually, two applications are required. The Cocoon is trawled on in a thick layer and left for about two weeks. It is then peeled off and discarded. The process is then repeated. Here is an example of salt damage on a harbour side property with airborne salt damage. We used Cocoon, repointed the stonework in a weak mix and installed a lead capping to protect the top surface of the stone.

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In my experience, it is critical that only a suitable mortar is used on stonework. Do not use hard cement mortars. Specialist advice should also be obtained before applying any sealer to stonework.

This following image is of a project we worked on with poorly done repairs. A very strong mortar was used to repoint. This meant any salts could not escape via the mortar joints. The second issue was the addition of a sealer. The salt could not escape via the mortar joints, built up and delaminated the surface of the stonework.

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Disclaimer: The information provided is for general informational purposes only, and we assume no responsibility for any issues that may arise from use of this information. It is not intended to be a substitute for professional advice. We recommend that only suitably qualified parties conduct thorough investigations for diagnosis or remedy, as each project is unique. Always seek the advice of relevant professionals as each project is unique.