The expansion behaviour of pre-compressed joint sealing tapes
Why is it not possible to define exact expansion times for joint sealing tapes and which factors influence their expansion behaviour?
Pre-compressed, impregnated joint sealing tapes made from flexible PU foam have been used for years in a variety of ways for sealing construction expansion joints. The main advantages of these sealing tapes lie in their permanent flexibility and their movement absorption properties.
The joint sealing tapes must meet DIN 18542:2009-07 defined properties such as a-value, driving rain resistance, building materials class B1/B2, sd-value etc., and they must be able to consistently demonstrate these properties during testing in high and low temperature ranges.
The delay in expansion is only needed for initial installation, as a so-called installation aid. An expansion delay is not a desirable property when it comes to the actual function of the joint sealing tapes. This is why the manufacturers set the expansion behaviour to a mean value that works in hot, medium and cold climates.
However, the expansion behaviour of the joint sealing tapes is still not constant but is influenced by a variety of different factors.
There are both physical and chemical factors.
The most important influencing factors include:
- Temperature of the joint sealing tapes
- Ambient temperature
- Rel. air humidity
- Material temperature of the surrounding building materials
- Storage conditions/climate (damp / warm / dry / cold)
- Storage time
- Age of the material
- Tape dimension
- Weather conditions (wind / sun / rain)
The above properties include tolerances and therefore do not allow any exact time period for the expansion of the joint sealing tapes to be defined.
Material that has been newly manufactured and expands in summer temperatures, will fill the joint faster than a joint sealing tape at low temperatures that has also been newly manufactured - even if there are other fixed influencing factors.
Expansion behaviour
If the ambient and material temperatures are over 25°C, the expansion behaviour is accelerated and it is recommended that the tapes are stored in a cool box. This will reduce the expansion time.
The expansion time is longer at temperatures between 15°C and 5°C.
At 5°C it can take over 24 hours to seal a joint. If the temperature is below the +5°C threshold then the expansion behaviour of the joint sealing strips is significantly slower.
In this case, the expansion behaviour can be accelerated by storing the tapes in a hot box or by warming them after they have been installed using a hot air blower (max. 80°C) and/or a warm water spray. ISO-TOP CLEANEX, a chemical expansion accelerator, is also available.
Note:
It is not advisable to store the joint sealing strips in vehicles for an extended period of time (e.g. overnight) during high summer or in winter if the temperatures are outside of the 10°C to 25°C range.