Relationship between pressure and adhesion
In the previous Fixcer Informa, we talked about how to measure the adhesion of a tile adhesive.
These adhesion tests are carried out in an official laboratory, and the results obtained are always reproducible in a laboratory. But how can the same results be achieved at the construction site?
The tensile adhesion test is carried out by gluing 10 pieces of porcelain tiles measuring 5 x 5 cm with the adhesive in question. The implementation is carried out as follows:
- a layer of tile adhesive cement is applied by combing it with a 6 x 6 mm toothed trowel.
- the notched trowel is held at an angle of 60° to the substrate.
- we apply a load of approx. 20 N for 30 seconds.
- the parts thus bonded are conditioned at 23+2°C for as long as the test requires, before being subjected to the mechanical tensile test.
Which of the factors described above will be of utmost importance in an actual on-site placement?
Undoubtedly, if we wanted to achieve the same results that are obtained in a laboratory, ALL factors would be of vital importance, BUT we are talking about a real job on site, so which factor is the most relevant?
A review of the above shows that a force of 240N (2 kg) has been applied for 30 seconds to the 5×5 cm pieces. (tiny). What force should we apply to a 30×30 cm piece? And to one of 120×60 cm !!!!!!!!? EXTREMELY HIGH.
The force equivalent to 20N (2Kg.) applied to a 5x5cm. piece is:
- for a 30×30 cm piece: 72 Kg. (!!!)
- for a 120×60 cm. piece: 576 Kg. (!!!!!)
The reality is that no one applies this kind of force, or rather pressure, on ceramic pieces. So how can we achieve an optimal result when actually placing them?
The purpose of pressing the parts for a certain time is to achieve an effective contact between the adhesive and the ceramic. This can be achieved by exerting the very high pressures described above or by using the double gluing technique: cement-based glue is applied to the substrate, but it is also applied to the back of the ceramic pieces.
It is vital to use good tile adhesive, and it is vital to use it with the correct technique.
