They are generally single
component, where the sealant cures by reaction to environmental conditions, or
dual component where the curing process is determined by the reaction of both
components when mixed together.
Sealants are characterised by their:
- Movement accommodation factor (MAF) - The total movement range a sealant can accept in
service, expressed as a percentage of the original joint width. MAF values for
joint sealants usually fall in the range of 5-25%.
- Shore ‘A’ hardness value - The sealant’s resistance to permanent deformation.
The above characteristics
are inversely proportional to each other. Therefore, choosing a sealant is
often a compromise between the two qualities.
When choosing a joint
sealant, some key aspects to consider are:
The anticipated joint
movement, ensuring MAF value is not exceeded.
- The width of the joint
opening at the time of installation.
- The pressures the sealant
will have to withstand from MHE etc.
- The temperature at
- How well the sealant will
adhere to the surface substrate.
- How quickly the sealant is
required to cure.
It is recommended to seal
joints as late as possible after construction to reduce the amount of movement
which will occur once the sealant is in place. It is normal to install a
softer, more flexible sealant in the early life of the slab, as this is when
the joints can be expected to open the most due to drying shrinkage and early
thermal contraction. Then, when it is thought that the slab will not shrink much
more, a harder sealant is installed to offer the joint arris more protection.
When applying a joint sealant, the area should be cleared of any moisture,
contaminents, oils, greases and loose materials.
The sealant needs to be
allowed to cure completely before it is trafficked. The rate of curing is
dependent on the ambient temperature, sealant type, humidity and dimensions of the
joint being sealed.
In the installation of a joint sealant, polybead foam is installed in
the bottom portion of the crack to suspend the sealant whilst it is curing.