Why can’t marble rust spots be directly cleaned with oxalic acid?

The common causes of rust spots on stone can generally be divided into two types: the first type is caused by the iron element contained in the stone itself. Generally speaking, each type of stone itself contains a certain amount of iron. When rainwater comes into contact with the iron in the stone, rust spots will slowly form, which are difficult to remove and require a longer time to process; The second type of rust spot is caused by external factors, such as residual steel sand or iron during construction, decorative metal components, and so on.

1、 What are the consequences of oxalic acid directly cleaning rust spots on stone?

1. Acid cannot wash away all the pollution from stone. Because the pollution that can be decomposed by acid belongs to alkaline pollution, and for acidic pollution such as pigments, acid washing is not scientific. Using alkali? It is also ineffective against alkaline pollution.

2. Destroy the stone structure. The main component of marble is carbonate, and even stable silicate granite contains easily decomposable components such as calcium carbonate. Carbonate components will decompose when exposed to acid. The main components are decomposed, and the surface structure of the stone will naturally be destroyed. Over time, it will be a matter of time before the stone loses its luster and becomes powdery.

3. Stone loses its luster. The most common consequence of using acid-washed stone, especially marble, is loss of gloss. This is related to the decomposition of calcium components on the surface of the stone.

4. The stone turns yellow. This yellowing, once it occurs, can be said to be widespread, especially in artificial stones. Because artificial stone is mainly made by pressing mineral powder, resin, etc., the resin will accelerate aging and turn yellow under the action of acid. The crystal layer of stone crystal polishing also contains a certain amount of resin.

5. Inducing various pathological changes. The infiltration of acidic solution into the interior of the stone can induce various pathological changes. The most common is rust yellow. Iron is easily oxidized into rust under acidic conditions. Stones with soft texture or high carbonate content, under the action of acid, will form pits, which are etched by acid.

2、 What should be noted when using rust remover?

A good rust remover not only contains acidic components but also an appropriate amount of additives to maintain the stability of iron ions in the oxidation-reduction reaction. Even without protective treatment, rust spots treated with this rust remover can remain for a long time without recurrence. On the contrary, some rust inhibitors are simply a mixture of acids that cannot maintain the stability of iron ions in redox reactions, resulting in high recurrence rates. Oxalic acid simply oxidizes and reduces rust spots, and the oxidized iron ions remain unstable. As long as it comes into contact with water and oxygen in the air, an oxidation reaction occurs, and then the flow of oxalic acid aqueous solution further expands the area of rust spots. Marble and granite have different compositions and properties.

The main component of granite is silica, which is acidic; So when using rust remover, it is important to distinguish between marble rust remover and granite rust remover. Granite rust remover should never be used for rust treatment of marble, and rust treatment can be divided into the following two situations: Of course, surface grinding and polishing methods can also be used.

Deep rust spots: require a certain dosage and reaction time to be maintained. Sometimes it may need to be reused to achieve the desired effect.

After using rust remover for construction, remember to clean the stone with clean water, and after drying, be sure to use a high-quality stone curing agent for protective treatment. The main purpose is to thoroughly remove the residue after the oxidation reaction and prevent the recurrence of the oxidation reaction.

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