THE OPEN TIME OF A TILE ADHESIVE
What is open time?
When using tile adhesive we must bear in mind an important technical fact: the open time. If the tile adhesive is fast-setting, this is essential.
But what is open time? Technically it is defined according to the standard as the “maximum time interval that may elapse after the application of the tile adhesive, during which the tiles can be laid in compliance with the adhesion specification according to EN 1346.”
In other words, let us imagine that we have a tile adhesive with an open time of 20 minutes and a theoretical adhesion of 1 N/mm2. The tile fixer laying the tiles mixes the tile adhesive with water and spreads it on the substrate. They then have a maximum of 20 minutes to lay the tiles. If it is done within the first 20 minutes, a certain adherence is guaranteed. For normal setting tile adhesives, the minimum open time required is 20 minutes. For quick-setting tile adhesives, the minimum open time required is 10 minutes.
It is very important to know the open time of the tile adhesive, as this will prevent the formation of a “surface layer”. When cement has been spread for a long time, water evaporates on the surface creating a “dry” layer which is very non-stick. If we glue the tile after the open time has elapsed, we have NO guarantee of a good grip and the tile could even fall off. The useful life time and the setting time are also different. They should not be confused with each other.
The useful life time refers to the “maximum time interval during which the adhesive can be used from the time of mixing”.
The setting time refers to the “maximum time interval during which a tile laid with adhesive can be adjusted without significant loss of adhesion.”
A typical example of normal-setting cement would be:
- Useful lifetime: 2 hours
- Open time: 20 minutes
- Setting time: 45 minutes
And a typical example of a fast-setting cement would be:
- Useful lifetime: 45 minutes
- Open time: 10 minutes
- Setting time: 15 minutes
