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Overlay of Existing Sealants

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:

  1. The existing joint must have enough exposed surface on both sides to allow for proper adhesion.
  2. There must be sufficient clearance to install the new sealant at a proper depth.
  3. 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.

Initial Rate of Absorption in Masonry

THE SIGNIFICANCE OF THE INITIAL RATE OF ABSORPTION

IN BRICK MASONRY WALLS

Masonry mortar must bond well to the masonry units in the wall. Brick absorption, including initial rate of absorption (IRA), is an important property affecting the bond. IRA also is a property for which a standard test method exists.

IRA and Bond
As hydration takes place and the mortar cures, chemical bonds form between mortar and brick. The brick must suck enough water and cement from the mortar to form these chemical bonds within its pores, while leaving enough water to allow cement hydration in the joint itself. IRA (expressed in grams of water per minute per 30 square inches of surface area) is a measure of this suction.

 

Water Retentivity
Water retentivity is a physical property of mortar, a measure of its ability to retain its mixing water under suction.

 

Methods to Enhance Compatibility
Masons can adjust their methods in various ways to minimize compatibility problems. With highly absorptive brick, the main concern is to prevent the mortar from drying out, so follow procedures recommended for hot-weather work. One way to reduce the absorptiveness of high IRA brick is to wet it before it is laid. IRA is only one of many factors that affect masonry performance. But matching mortar properties to the brick's absorption rate can contribute to strong, complete bond.

Caulking | Restoration | Arlington Heights | Illinois | Sealant | Replacement | Coating | Caulking | Tuckpoitning | Masonry | Chicago | Illinois | Wisconsin | Indiana | Balcony | Repair | OSHA | Contractor | Indianapolis | Safety |
Caulking | Restoration | Arlington Heights | Illinois | Sealant | Replacement | Coating | Caulking | Tuckpoitning | Masonry | Chicago | Illinois | Wisconsin | Indiana | Balcony | Repair | OSHA | Contractor | Indianapolis | Safety |
Caulking | Restoration | Arlington Heights | Illinois | Sealant | Replacement | Coating | Caulking | Tuckpoitning | Masonry | Chicago | Illinois | Wisconsin | Indiana | Balcony | Repair | OSHA | Contractor | Indianapolis | Safety |

Unique Sealant Failures

It's not every day that we see both an adhesive and cohesive sealant failure at the same location:


Improper joint design, poor material mixing, incorrect sealant selection, sub-par preparation; all leading causes of premature joint failure. The example shown below is a very uncommon example of joint failure. The main failure on this joint was an adhesive failure, meaning the sealant lost adhesive to the substrate. But in one lone area, there was a cohesion failure, which is highly unlikely to occur. Generally, an adhesion failure will continue throughout an entire joint due to improper preparation and installation. In this case it looks like one specific spot was prepared correctly but the caulk was installed too thin. Regardless of the cause of failure, this building certainly needs 100% of its sealants replacement. 


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J.S. Goray Inc.

951 N. Old Rand Rd., Suite 112

Wauconda, IL 60084

(800) 516-3074