Joint sealants need to be chosen and used in line with the recommendations in BS 6213.
Given that different sealants’ characteristics might differ, it is important to heed the advise of sealant makers. A sealant should be able to survive the typical service conditions impacting the installation, such as resistance to water, ultraviolet radiation, etc., and be able to accommodate the expected amount of movement without losing adhesion to the edges of the joints.
Class 25 sealants have to be used when movement joints are meant to cover structural joints and there is a chance of frequent movement. Classes 20 or 12.5 should be taken into consideration for joints that move less often and with lesser movements.
NOTE 1 A broader joint, a more flexible sealant, or a combination of the two can support a certain amount of movement; nevertheless, if the class number is less than 20, the sealant might not be appropriate over structural movement joints. The higher sealant class required to allow for a particular amount of mobility depends on how small the joint is.
Backer Rod (Sealants and backer rod)
A material that the sealant cannot stick to or that may be wrapped with bond breaker tape to prevent adhesion should be used as the compressible backup material.
The back-up material utilised in the joint’s bottom portion needs to work well with the sealant being applied, be resilient after compression, and sustain the sealant. It shouldn’t absorb an excessive quantity of moisture or release bituminous or greasy substances.
In particular, it should be compressible enough to prevent the sealant from being driven out as the joint closes. Closed cell cellular rubber, polymers such cellular polyethylene, certain fibre construction boards, cork boards and mineral or synthetic ceramic cables or blankets are typical materials that should be employed.
NOTE 1 There are many sizes of backup materials in sheet, strip, and cord form. Sealants and backer rod
NOTE 2 For further details on setting up backup supplies. Sealants and backer rod