Why clean marble without using aggressive acids?
The majesty of the marble hides a surprising chemical vulnerability. Considered eternal, this natural material is actually the expression of a delicate balance of minerals that can be seriously compromised by the smallest of gestures. acids, even those contained in substances that seem harmless to us, corrode marble. In some cases, instantly.
Behind the surface of this precious stone, in fact, there is a saline architecture that does not escape the laws of chemistry.
Why do acids ruin marble? The chemical explanation
Marble is a solid and very durable stone, resistant to impacts and capable of bearing heavy loads, but it is also a porous and very delicate material, which is sensitive to water and acids. Leaving marble wet for a long time can dull it and lead to the formation of stains that are very difficult to remove. Using an acid on a marble floor or countertop, however, has decidedly more disastrous effects.
- acids – all acids, even those that may seem most harmless to us – are marble's main enemy. And behind this enmity, obviously, is chemistry. Marble is a rock composed almost entirely of calcium carbonate (CaCO3), an inorganic salt which is itself made up of the union of two electrically attracted parts, the calcium cation (Ca2+) and the carbonate anion (CO32-).
As long as they remain united in their crystalline lattice, these ions form a very hard and compact stone. However, when an acid comes into contact with the marble, a disruptive chemical reaction: pouring acid on calcium carbonate means releasing some hydrogen ions (H+), which have a much stronger chemical attraction for the carbonate than the one that keeps it bound to the calcium. The acid, therefore, attacks the carbonate ion, binding to it (and thus "tearing" it away from the calcium).
When two hydrogen ions bond to carbonate, they generate carbonic acid (H2CO3), an extremely unstable compound that tends to instantly transform into water and carbon dioxide (clearly visible in the classic bubbles that form when you pour strong acid on marble). The calcium, in all this, left without its negative counterpart, becomes a free ion, then detaches itself from the stone and binds to the negative part of the acid, giving rise to a salt that is extremely soluble in water, and therefore very easy to carry away while cleaning. And this is how the marble surface corrodes, losing its compactness and therefore its ability to reflect light.
Acid-Free Marble Maintenance: The Hidden Dangers
The damage caused by acids on marble can go far beyond the instantaneous corrosionMarble is a highly porous material, so once the acid has attacked the surface layers, stains can penetrate deeply and become virtually impossible to remove. Cleaning marble without acids is a fundamental rule, and as mentioned, this also applies to some acids we tend to consider harmless.
Some natural substances, perfect for cleaning glass and other materials, can be lethal for marble.vinegar for example (even that of dish soap) contains acetic acid and therefore corrodes marble in a few seconds, while the juice of Lemon; It contains an acid that's even more aggressive than calcium carbonate. Such substances can dull (see: wear away) the surface in a matter of moments.
Another product that should never be used on marble isanti-limescaleIts function, in fact, is precisely to dissolve calcium carbonate, which makes up limestone but also our precious natural stone. Other enemies of marble include:
- Wine and fruit: contain tartaric acid and malic acid. White wines and fruit juices in particular can corrode marble, although more slowly than lemon;
- Sodas: they are rich in orthophosphoric and citric acid;
- Milk and yogurt: bacterial fermentation produces lactic acid, a slow but effective corrosive agent;
- Bathroom products and descalers: based on hydrochloric or sulfuric acid, they cause deep and immediate damage;
- Cosmetics and creamsMany facial serums, anti-aging creams, and exfoliants use glycolic and salicylic acids to remove dead skin cells; however, these same acids can affect marble sinks.
Marble Maintenance: The Neutral pH Rule
The most sensible strategy to avoid damaging the marble is aim for neutral pH, that is, use substances and products with a pH of 7 (or as close to this degree of acidity as possible).
To summarize this concept:
- Acids (pH less than 7): they have a high concentration of H+ ions, responsible for the breakdown of calcium carbonate;
- neutral pH (equal to 7): substances with this degree of acidity, such as pure water, do not contain enough free H+ ions to trigger the reaction that corrodes the marble;
- Bases, or alkaline (pH above 7): the quantity of H+ ions is so insignificant that they are neutralized even before touching the stone. For this reason basic substances such as Marseille soap (pH 9-10) and ammonia (pH 11) can be used on marble.
The bases, however, require caution: if it is true that they can be used ammonia and bleach While it's true that marble isn't 100% calcium carbonate, it's also true that marble isn't made of calcium carbonate. Floors and coverings may contain metals and organic impurities that can react with the bases, causing corrosion over time. brown or yellowish spots. Furthermore, if a strong base penetrates the pores and is not rinsed off, it can form different salt crystals that, expanding, create micro-cracks in the marble.
The other properties of a substance must then be considered: the bicarbonate, for example, has a fairly neutral pH, but is highly abrasive, so it can dull marble (even if diluted in water).
Why choose gentle detergents to clean marble?
A neutral pH, in itself, is not sufficient to guarantee the health of the marble. A neutral detergent may contain perfumes, colorants or thickeners In large quantities: these substances are not corrosive, but they can leave residues that over time attract dirt and damage the stone. Too "strong" products, such as some degreasers, can attack protective treatments like waxes and waterproofing agents, leaving surfaces dangerously exposed.
Cleaning marble also requires a certain delicacy. The most suitable method for daily cleaning involves the use of warm water, neutral detergent (or Marseille soap) and soft microfibre cloth. If the need is to sanitize surfaces, however, you can use someethyl alcohol Diluted in water, it has a nearly neutral pH and evaporates quickly without leaving streaks. Finally, for polishing marble, a soft wool or microfiber cloth is sufficient.
Despite some effective "home remedies," it is still advisable to choose a neutral detergent specifically formulated for delicate surfaces. Specific products, in fact, contain seizing agents, which prevent minerals from depositing on the marble, and selected surfactants (also of plant origin) which allow for deep cleaning without damaging the material. Furthermore, the detergents are designed to have a stable pH constantly between 7 and 8.
