Silicone types in common use in our industry include:
- Neutral cure – Acetoxi cure
- High Modulus – Low modulus
Is there much difference, and does it really matter?
The answers to these two questions are Yes, and Yes.
The cost difference between Acetoxi cure and Neutral cure can be quite a few pence a tube, and as many in the industry seem to think that ‘it is all the same’, some are often repeatedly using the wrong type of silicone for the job.
Silicone sealants are classified for use in either a) glazing joints, or b) for building joints other than glazing. There are further classifications to do with how well the movement capability is accommodated. The movement accommodation of the higher % ones (20%+) are then classed into low modulus and high modulus.
The meaning of high and low can be explained simply: a low modulus will need just a low force to stretch it and will have better elasticity and movement accommodation, a high modulus is more rigid. In deciding which modulus is best for a given application, desired movement accommodation is the main thing to take into consideration. In our industry it is generally accepted that linear expansion and contraction of the plastics we use, joint movement itself can be reckoned to be high, therefore a low modulus silicone should be used to accommodate such expected movement. Some of the better silicones boast being able to accommodate movement of up to 50% of the nominal joint width.