Suitable for internal and external application on metal or timber window and door frames, Cornerstone Burnt Sand Mastic offers a versatile sealing and repair solution. Note that Cornerstone Burnt Sand Mastic should not be used for repairing damaged rises or defective renders. Ensure all necessary repair work is completed thoroughly before applying the mastic.
The product is supplied in two components: 16kg of burnt sand and 2.5L of oil driers, forming an oil blend. This creates a standard volumetric mix ratio of four parts powder to one part oil, ensuring optimal performance.
Preparation
Surface preparation will vary depending on the substrate and intended use. Generally, ensure surfaces are thoroughly clean, free of dust and debris, and that best practices are followed. Coverage varies with joint depth and size; therefore, conduct a test on a small area to estimate the coverage for your project.
Before pointing, tightly pack wide gaps between the frames and masonry with cured, hardened fibred or well-haired lime mortar, keeping the joints slightly recessed by 4-5mm. Use a small painter’s fitch brush to apply a light primer coat of oil dryers to the frame and adjacent masonry, ensuring the line of the planned mastic joints is maintained.
Mixing
- Mix only the amount you can use within a few hours. Ensure thorough mixing with the minimum amount of oil.
- For optimal colour results, mix the entire tub at once. Refer to the datasheet for detailed mixing instructions.
Application
Cornerstone Burnt Sand Mastic can be applied using various tools, depending on the joint width and depth, to ensure optimal results. Standard tools include a mixing pot, a small hawk or mastic box, a proprietary mastic trowel, a painter’s fitch brush, or a small tool suited for precise application. To maintain tool cleanliness and prevent contamination, always wipe tools with an oiled cloth during application and clean them thoroughly afterwards with an appropriate cleaning solution.
When applying Cornerstone Mastic, press it firmly into the angle of the frame or jamb, filling from the bottom up to create a clean 45-degree joint.
- Begin at a corner, and using a clean, oiled mastic trowel, press against the timber frame and masonry jamb.
- Carefully draw the trowel to form a neat, even fillet, removing any excess mastic as you go.
- Finish by wiping the timber edges for a polished look.
For mastic application on sills, ensure the bead does not bridge any drips and remains recessed behind the drip check. The mastic fillet should be neatly shaped, measuring approximately 20 to 25mm across the diagonal face for a professional finish.
Aftercare
Aftercare for burnt sand mastic requires sufficient time for curing and full hardening. The curing period varies with environmental temperature, typically 1 to 3 weeks.
To ensure optimal results, it’s recommended to protect the freshly applied mastic from direct sunlight and wind by covering it with hessian or plastic sheeting to create a barrier against environmental factors.
Materials containing oils, such as paper towels or cloths, should be soaked in water before disposal to minimise fire risk in warm conditions. Consult the product datasheet for detailed health and safety information related to oil-based materials.
For comprehensive product details, application instructions, and datasheets, refer to the Technical Data and Documentation section. Always review these documents before applying.
Please note:
The Mastic does not require painting. If a change of colour is desired, the mastic should only be painted once it has cured, using a linseed oil-based paint.
The product is supplied in 2 parts:
- 10 litres of Burnt Sand
- 2.5L Boiled linseed oil
Downloads
For more detailed information and application guidance, please refer to the datasheets available below:
- Cornerstone Burnt Sand Mastic - Technical Datasheet (PDF)
- Cornerstone Burnt Sand Mastic - Safety Datasheet (PDF)
- Cornerstone Burnt Sand Mastic - Application Guide (PDF)
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