Overlay: When Is It Appropriate?
Leaving existing joint sealant in place and installing an overlay of new sealant can be an option if the conditions allow. While this could be considered a cost saving technique, the majority of existing conditions would not be acceptable for this technique. While it would save the installer time, in addition to material, by not removing the existing sealant, it mostly results in improper joint design and extremely premature failing of system. Below is a excellent example of what not to do when attempting to overlay joint sealants.
To successfully perform a joint sealant overlay the existing conditions must be present:
- The existing joint must have enough exposed surface on both sides to allow for proper adhesion.
- There must be sufficient clearance to install the new sealant at a proper depth.
- A bond breaker, generally a polyethylene tape, must be installed over the existing sealant to prevent three-sided adhesion.
The detail below illustrates the proper joint design in regard to depth and width that must be applied in a joint sealant overlay project.
Note: the “green” back rod would be existing sealant with bond breaker tape.