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Tiling guide: Tips to overcome moisture mark stains on marble and granite floors

21 Jul 2020 by MAPEI

Stones (marble and granite) are natural products and they can be porous and moisture sensitive. To identify porous tile or stone, drop a small amount of water on the surface and you can see that water slowly gets absorbed into the surface. The natural structure of the stone has open pores that allow moisture to enter and create moisture mark stains or discoloured patchy areas after they dry out. Porosity ranges differently by stone type.

When installing stones on floors or walls, installers may come across staining on stone surfaces a few weeks or months after complete installation. Stains are unsightly and can be difficult to remove. It can result in retiling which is time consuming and expensive. However, it is possible to prevent this phenomenon.  

Tiling guide: Tips to overcome moisture mark stains on marble and granite floors

Reasons for moisture marks

Moisture marks in the stone installation are mainly caused by:

  • The stones are not able to dry properly.
  • Highly humid and poorly ventilated environments.
  • High residual moisture in the screed mortar.

Preventive measures during installation

Prevention is always better than cure. So, what can be done to prevent the issue of moisture mark stains on stones?  

1. Use fast-setting adhesives with rapid hydration property

Fast-setting adhesives* are effective in combatting humid and poorly ventilated site conditions and stones that are sensitive to moisture. The setting time for the adhesive to cure is rapid such that the moisture residual content is greatly reduced. Fast-setting adhesives are denoted by class F. Its characteristics include early tensile adhesion strength to be at least 0.5 N/mm² after just 6 hours (in accordance to the standards of EN 12004 & ISO 13007-1).

2. Use Reactive adhesives

Reactive adhesives^ typically come in the form of epoxy-based or polyurethane-based. They do not contain water and hence present less issue with moisture absorption. Reactive adhesives are classified as “R1” if their shear adhesion strength is 2 N/mm² after dry curing and immersion in water. Class “R2” is used for products that have a shear adhesion strength of at least 2 N/mm² after thermal shock. Open time for all reactive adhesives must be at least 20 minutes with tensile adhesion strength of at least 0.5 N/mm2. 

3. Substrate Preparation

It is important to ensure that the substrate is properly cured, completely dry and that all hygrometric shrinkages have taken place. Screed mortar beds are to dry out in a well ventilated environment and with low percentage of residual moisture content before carrying out the stone installation. Take care not to cover the floor with protection too early. 

When in doubt, conduct site trials to establish stone’s sensitivity to moisture by observing stone’s reaction towards normal-setting and fast-setting adhesives. Doing things right the first time can eliminate costly mistakes and rectification work.

* Our range of Rapid setting adhesives: Keraquick S1, Granirapid, Elastorapid

^ Our range of Reactive adhesives: Kerapoxy Adhesive, Keralastic, Keralastic T

Contact Mapei Singapore for your projects.


About Mapei:

Founded in Milan since 1937, Mapei is today a world leading producer of adhesives and complementary products for the laying of all types of floor, wall and coating materials. Mapei’s specialty lies in products for ceramics and stone materials, among other product lines. Mapei’s tile adhesives are certified according to international standards and are SGBC certified in Singapore. Experience proven by numerous notable projects worldwide.

Related articles on Stone & Tile Adhesive installation:

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Founded in Milan in 1937, Mapei is today the world leader in the production of adhesives and chemical products for the building industry. We implemented our internationalisation strategy in the 1960’s and this has enabled us to be closer to the needs of regional markets and reduce transport costs to a minimum. The Group now has 89 subsidiaries with 83 production facilities in 36 different countries. We have always placed a lot of emphasis on research. In fact, we channel 5% of annual turnover into Research & Development and 70% of our research work is aimed at the development of eco-sustainable and eco-compatible products.An unrivalled offerOur products offer clients the most specific and most advanced solutions in the world of building. Users of Mapei products can see for themselves, day after day, how this choice leads to optimising work, maximum application yield and perfect results, under all conditions. We are not just a supplier; we are also a partner for all those who operate in this sector with a comprehensive range without rivals. Our name is synonymous with innovation and every year we create thousands of new formulations to meet all your needs. We supply more than 5,000 technologically advanced products worldwide that take into consideration the widest variety of requirements imaginable and, in so doing, we help improve the characteristics of buildings, from anti-seismic upgrading to the healthiness of our surroundings.Expertise in the construction sector born from on-site experienceThrough a constant exchange of ideas and experiences with clients and builders’ merchants, we use their input as a starting point to shape innovation and reformulate their suggestions in the form of new products to expand the range of lines and references. From the smallest to the largest sales points for ceramics and building materials, our quality is not limited to the product itself, but extends to the competence of the sales team, the passion of our retailersand the value of their advice. Our clients can also take advantage of our Technical Services Department and their constant, expert support, from the design phase right up to the execution phase, to guarantee an end result that will always live up to their expectations.


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