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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.
Reasons for moisture marks
Moisture marks in the stone installation are mainly caused by:
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.
Contact Mapei Singapore for your projects.
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.
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