In short, it is generally not recommended to apply thinset over cured mastic. The reason for this is that thinset mortar requires a clean and stable surface for proper adhesion. Since mastic can form a smooth and impenetrable surface, it can hinder the bonding and penetration of thinset mortar onto the substrate.
The Risks and Challenges of Applying Thinset Over Cured Mastic:
Although it is technically possible to apply thinset over cured mastic, it poses several risks and challenges:
- Poor bond strength: The presence of a cured mastic layer can interfere with the bond strength of the thinset mortar. This can result in tiles that are not securely held in place, leading to potential issues such as cracked or loose tiles.
- Lack of adhesion: Mastic is generally not as porous as cement-based thinset mortar. This lack of porosity can impede the adhesion of the thinset to the surface, causing it to fail in the long run.
- Inconsistent curing: Thinset mortar requires proper curing to reach its optimal strength. If the underlying mastic layer prevents proper curing, it can lead to weaker overall adhesion and performance of the tile installation.
Removal of Cured Mastic:
Instead of attempting to apply thinset over cured mastic, it is recommended to remove the mastic layer altogether. This can be done using a variety of methods, such as scraping, chemical removers, or mechanical tools. It is important to ensure that the surface is clean and free of any contaminants or remnants of the mastic before applying thinset.While it may be tempting to save time and effort by applying thinset over cured mastic, it is generally not recommended. The challenges and risks associated with poor adhesion and bond strength make it a less desirable option. Instead, it is advisable to remove the cured mastic layer and prepare the surface properly before proceeding with the tile installation. By doing so, you can ensure a strong and durable outcome for your tiling project.