The sealant template, which is regularly designed as a masking tape , limits the penetration depth of the sealing material (and thus, in the case of plastic materials, its layer thickness) and prevents the seal from disappearing into the depths of the joint. The tape itself does not have a sealing function.
The sealant template is of particular importance in the case of plastically applied ( injectable ) sealants that cure elastically (such as silicone rubber ), as it prevents the sealant from sticking to the joint base.
The permanent adhesion of the sealant to the two flanks of the joint is best when the two lateral adhesive surfaces are as large as possible, but only low tensile stresses arise within the sealant in the joint space between them when there is thermally or statically induced movement of the components against each other.
This is exactly what is achieved by using a round cord as a tape. The round cord reduces the cross-section of the sealant in the middle of the joint, so that the tensile forces acting on the flanks are significantly reduced when the joint width increases.
The dimensioning of the seals and the resulting required sealant template is stipulated in standards for the individual trades or is specified by the manufacturer according to the individual approval of the sealant.