Joint Sealant

Summary

Joint Sealant - Joint Sealants are supplied as liquids or paste-like materials that cure to create a flexible seal.

Technical Information

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 installation.
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.