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For architects and designers · Guide no. 3

Damp stains on marble and granite: why they appear after installation and how to prevent them

This is the most frequent complaint on natural stone floors and stairs. It almost always stems from a choice made at the installation stage.

Articles · 5 min read

The floor has just been handed over and, after a few weeks, darker patches appear, marks that no cleaner will remove. The client calls, the installer blames the material, the supplier blames the installation. In most cases it is installation moisture: a problem that can be prevented with a single step.

What is the most frequent complaint?

Damp stains that alter the colour of marble, granite and engineered stone. They are almost always due to an installation method unsuitable for the material and, once they appear, often cannot be removed.

The mistake to avoid: laying natural stone on a cement bed

Screed and cement mortar take about a month to dry out completely. During this time the moisture, together with salts from the cement and sand, evaporates upwards and is absorbed by the stone. The result is darker or lighter patches that follow the shape of the mortar beneath the slab.

Note: these stains are easily confused with oil stains, and vice versa. Before acting, identify the cause: oil requires a stain remover such as MGP 2, damp requires a specific treatment.
D-DAMP test on granite immersed in water
Test on a highly absorbent granite immersed in water for more than 24 hours: the treated part does not absorb moisture.

How can damp stains be prevented?

By treating the material with a damp-proof protector before installation, on the back and edges of the slab. A simple water repellent is not enough: you need a product that stops moisture rising even when it is present in large amounts.

And if the floor is already laid? The same treatment, applied to the surface only, stops moisture from rising: you can intervene successfully even after installation, limiting the damage and its spread.

The solution

Before or after installationD-DAMP / D-DAMP K – Damp-proof protectorAgainst rising damp on marble, granite and engineered stone. Prevents stains and haloes caused by cement and adhesives. Solvent-based (D-DAMP) or water-based (D-DAMP K).

What to write in the specification

· installation of marble, granite and engineered stone with suitable adhesives, not on a cement bed, respecting screed drying times;
· D-DAMP damp-proof treatment on the back and edges of the slabs before installation;
· on existing floors with visible damp: D-DAMP surface treatment.

Do you have a floor with damp stains?

Send us a photo: we will help you work out whether it is damp, oil or something else, and what the correct treatment is.

Ask for technical advice

All articles

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Designers' areaReady-to-copy specification clauses, technical data sheets, a job-site guide and a test kit with samples for your own tests.