Stone joint grout KSL black grey

Base

• Slate or other jointed materials must be installed on a concrete substrate, and the stone joint mortar is applied between the jointed materials on top of the solid concrete base.
• The substrate temperature must be between +5°C and +25°C.
• The concrete substrate must be solid, clean, dust-free, and free from grease. Cement laitance and other impurities must be removed mechanically to ensure proper adhesion. The best bond is achieved on a rough surface.
• If necessary, protect the jointed material from staining caused by mortar splashes. Using a Fescoblaster FBL mortar pump significantly facilitates the grouting process by allowing clean and accurate mortar placement into the joints.

Priming

• The concrete substrate must be moistened with water to a matt-damp condition to prevent a dry base from absorbing moisture from the joint mortar. There must be no standing water or puddles on the surface.
• It is recommended to start moistening the substrate the evening before installation to allow the water to penetrate deep enough. In renovation projects with very dry and absorbent structures, repeated moistening is recommended.
• Do not use separate liquid bonding primers.

Mixing and application

• The work area must be protected from strong wind, direct sunlight, and rain.
• During mortar application and curing, the air and substrate temperature must be between +5°C and +25°C.
• One 25 kg bag of dry powder is mixed with 3.4–3.6 litres of clean water. We recommend starting with the minimum amount of water and adjusting as needed. The specified water amount must not be exceeded, as it weakens the strength properties, increases the risk of segregation, and prolongs the drying time. For vertical surfaces, the correct consistency is achieved when the product does not run during application.
• Mixing time is 2–3 minutes with a paddle mixer or 10 minutes with a concrete mixer. After mixing, allow the mortar to stand for 10 minutes, then briefly remix.
• The working time is approximately 2 hours after mixing.
• The product can be applied using a Fescoblaster FBL mortar pump or manually with, for example, a steel trowel. The finished surface should be smoothed to the desired finish level using a jointing tool and/or steel trowel. Surface finishing is performed when the mortar has slightly dried.
• The recommended maximum layer thickness is 50 mm. Thicker layers should be built up in multiple passes, allowing each previous layer to cure for at least 24 hours before applying the next one. The surface of the previous layer should be left as rough as possible to ensure good adhesion. If needed, the previous layer can be moistened to a matt-damp condition.
• Clean tools with water immediately after completing the work.

Curing

• The surface must be kept moist for 2–5 days, depending on conditions and the project, using either water misting or plastic sheeting.
• It is essential to ensure adequate moisture during the curing process to allow proper hydration and to achieve the desired strength. This also helps to prevent potential plastic shrinkage cracking and detachment from the substrate.
• Especially in spring and in heated spaces, curing must begin immediately and be carried out carefully, as the relative humidity is often below 40% RH. Low ambient humidity, combined with sunlight and wind, causes the surface to dry very rapidly.

Other Considerations

• The cured product can only be removed mechanically.
• Use of the product in cold and damp conditions significantly increases the risk of light-coloured efflorescence appearing on the mortar surface. Normally, efflorescence will fade over time due to rain and natural wear.

Storage and handling of waste
See the separate storage and disposal instructions https://www.fescon.fi/en/material-bank