Floating a Buttering

Floating and Buttering in Tile Adhesion 

1. Definition of Terms

In tiling practice, the terms floating and buttering are commonly used to describe methods of applying tile adhesive.

• Floating refers to the process of applying adhesive onto the substrate (wall or floor). The adhesive is first spread with the smooth side of the notched trowel to create a continuous layer, and then combed with the notched side to form ridges in a uniform direction.
• Buttering means applying a thin, continuous layer of adhesive onto the back of the tile. The purpose is to improve adhesion and ensure full contact between the substrate and the tile.

The combination of these two methods – known as floating–buttering – represents the standard approach, especially when working with large-format tiles.

2. Issues and Challenges

Incorrect application of tile adhesive is one of the most common causes of tile defects and subsequent claims. Typical problems include:

• Voids between the tile and substrate – the tile is not fully supported across its surface. These voids act as stress concentration points where tiles can crack under load.
• Moisture retention – water can penetrate into unfilled areas, leading to adhesive degradation, frost damage, and eventual detachment of tiles.
• Insufficient coverage – according to European standards (e.g. EN 12004), minimum coverage is 80% for interior applications and 90–100% for exterior, wet areas, or large-format tiles.

Another recurring problem is the incorrect direction of adhesive ridges. If ridges are applied crosswise or in arcs, trapped air cannot escape when the tile is pressed in. This results in voids, which pose a structural risk and are considered a breach of proper installation practice.

3. Correct Procedure

The proper technological procedure for applying tile adhesive consists of the following steps:

1. Substrate Preparation
   The substrate must be solid, stable, flat, clean, and free of dust, grease, or weak layers. Absorbent surfaces must be primed.
2. Applying Adhesive to the Substrate (Floating)
   Adhesive is spread with the smooth side of the trowel, then combed with the notched side to create ridges in one uniform direction (vertical or horizontal). The notch size depends on the tile format – from 4 mm for small tiles up to 10–12 mm for large-format units.
3. Applying Adhesive to the Tile (Buttering)
   A thin continuous layer of adhesive is spread on the back of the tile with the smooth side of the trowel. This evens out irregularities and enhances adhesion.
4. Combining Both Layers (Floating–Buttering)
   The tile is placed onto the adhesive bed with ridges and gently pressed or moved back and forth. This causes the ridges to collapse into the thin layer on the tile, filling the entire space between the tile and substrate. The result is full adhesive coverage without air voids.
5. Coverage Check
   One tile can be removed as a test to verify adhesive coverage. For interior installations at least 80% coverage is required; for exterior or wet areas 90–100%.

4. Conclusion

Proper application of floating and buttering methods is a key prerequisite for long-lasting and defect-free tiling systems. Mistakes in adhesive application – particularly insufficient coverage and incorrect ridge direction – are a frequent cause of defects and claims.

As a professional expert witness, I conclude that strict adherence to tiling technology is essential. The use of the floating–buttering method, correct choice of notched trowel, and maintaining a uniform ridge direction are mandatory to achieve the required performance. Failure to comply with these principles can be evaluated in expert reports as a technological fault of the contractor.