Reasons for moisture marks
Moisture marks in the stone installation are mainly caused by:
- Stones 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 marks on stones?
1. Use fast-setting adhesives with rapid hydration property
Fast-setting adhesives* are effective in humid and poorly ventilated site conditions, especially for 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 - at least 0.5 N/mm² after only 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 types. They do not contain water and hence present less issue with moisture absorption. Reactive adhesives are classified as follows:
- “R1” if their shear adhesion strength is 2 N/mm² after dry curing and immersion in water.
- Class “R2” if their shear adhesion strength is 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, to assist in drying.