Exposed Silicone Joints
Sealant is the most versatile and commonly employed sealing method around bath and shower receptors. There are two golden rules in the proper use of sealant if intended to accommodate joint movement:
1. For sealant to stretch freely between the wall and ledge, it is important that it is prevented from making contact with any other surface. ‘Three side adhesion’ must be avoided because is restricts movement between the ledge and wall and creates stress that often results in tearing or de-bonding.
For this reason, surfaces and voids adjacent to the wall and ledge that may unintentionally be engaged with sealant during the sealing process should be coated and/or shuttered off with a sealant bond-breaker tape/backing material.
The concept of using sealant bond-breaker and backing materials is to create a sealant ‘bridge’ between the wall and ledge that sealingly elongates with minimum stress and accommodates joint expansion without splitting or de-bonding.
This practice is promoted by sealant manufactures and Building Standard bodies throughout the world.
2. Sealant flexibility is referred to as the ‘Movement Accommodation Factor’ (MAF) or CLASS and generally measured as a percentage of the extensibility and compressibility when the sealant is cured and in the rested state. A sealant with MAF of +/- 25% (CLASS 25 sealants) will extend/compress 25%.
Sealant with MAF of +/- 25% (CLASS 25) required to accommodate 2mm wall/ledge joint expansion after installation, must have a minimum unobstructed sealant ‘bridge’ of 8mm. Allowing for the fact that this 8mm ‘bridge’ represents the under belly or hidden face of the sealant and further 4mm sealant depth is required to bridge the wall and the with the ledge, the resultant exposed face is a substantial
Sealant exposed to the shower environment tends to act as a magnet for shower waste matter to form an unsightly unhygienic film over the sealant that accelerates the deterioration process. The rubbing of sealant during the cleaning process can often results in ‘tearing’ over time or ‘de-bonding’ from the wall or ledge surface especially if such seals already in a poor state.
In many circumstances, the aesthetic and hygiene issues associated with exposed sealant in shower environments prompts installers to minimise sealant visibility, this in turn impacts upon the capacity of the sealant to stretch and accommodate joint movement often leading to splitting or de-bonding and eventually a leak.