We never know where these stains come from or much less how to get rid of them, but they are called saline or salt efflorescence.
Saline or salt efflorescence is, fundamentally, sodium or potassium salt that accumulates in the form of crystals on the surface of concrete wall coverings, natural stone or brick. Therefore, when we touch the stains they can remind us of the salt residue that can be left on our hands when we are cooking, or that the sea leaves behind on rocks.
To diagnose if our wall has been targeted by this unappealing efflorescence, we need to pay attention to the appearance of the off-white and irregularly shaped stains on the surface of the façade. More than just being an aesthetic issue for the walls or surfaces, it can also end up causing deterioration of the material that it has appeared on. These are normally materials that are located outside of our homes, and can therefore cause problems that are far more serious than aesthetic issues.
Salt? But my house is not by the sea! Where do these stains come from? How can they have formed on my walls?
All of these questions are answered through the knowledge that the salt present in the material used to construct walls, once it gets wet by any means of exposure to water, will be dissolved to the surface through a process of capillarity. When this water evaporates, the salt crystallises and accumulates, forming the whitish dust that bothers us so much.
Some of the factors that lead to the appearance of salt residue or efflorescence are:
- The use of very porous materials in construction.
- The use of aggregate with a high level of salt.
- Plaster mortar that hasn’t cured well enough, prior to applying the final coating.
- Mortar applied in high humidity, or on rainy or cold days.
- Moisture, mainly capillaries.
- Or the use of calcareous water during the cement mixing process.
How could I have prevented the appearance of efflorescence?
The preventative measures to employ prior to construction are:
- Preparation of the material to be used for construction of the wall or substrate.
- Not using hard water when mixing mortar.
- Using low-alkaline mortar to avoid the formation of salt. In this cases we recommend using mortar for reparation, such as Plasmont Exteriores or Plasmont al Uso Reparación Fachadas
The preventative measure to employ during the construction process is:
- Stick closely to the correct curing and setting times of the mortar and filler.
Another essential preventative method is to eliminate moisture.
If you don’t eliminate it completely, it could appear again and then all the reparation work will have been for nothing. Depending on the type and the cause of the humidity, we have a method to eliminate it
- With a good waterproof paint, if the problem is moisture due to filtration. For this we would recommend products such as Montokril Elastic or Tejamont from Pinturas Montó.
- With a good insulation system, if the problem is moisture due to condensation. Pinturas Montó would recommend Magnum Termoaislante Anticondensación for indoors or the Sistema Montotherm (SATE) for outdoors.
- If the salt residue comes from underground moisture (capillary moisture), the solution will require some type of constructive protection.
How can I repair the damage that the efflorescence has caused to my walls?
To repair the salt stains you would generally need to clean and apply new protection to the substrate.
Cleaning: Simply clean the entire stain with natural water and a brush. Occasionally it may be necessary to use an acid cleaner to neutralise and eliminate the salt residue. In extreme cases it may be necessary to use mechanical tools to eliminate it.
It is very important to let the substrate dry fully after this cleaning process.
To finish the process you will need to renovate the wall’s protection with reparation mortar (if you need to repair flaws in the substrate) and with paint.
As with mortar, remember it needs to be free from alkalinity. For the final coating, depending on the type of finish and protection you want to use, you can find multiple options, for example in the Ovaldine range, which are as effective inside as they are outside.
To use the common case of face brick walls as an example, you would have to protect them with a protective waterproof varnish for porous surfaces, such as Uno Barniz Ladrillo, or with a water repellent like Impersil
To finish, you may have noticed that only a small part of the house’s walls have this problem, but nevertheless you will have to repair more than just the damaged wall. It’s advisable to pre-empt future potential problems and protect all the areas that could be susceptible to this issue, and therefore prevent further outbreaks of efflorescence on your walls.