Page 279 - Construction Waterproofing Handbook

5.38 CHAPTER FIVE
This may require mechanical methods such as grinding or sandblasting. It is important to
note that after mechanical cleaning, joints must be recleaned to remove dust and residue
left behind by mechanical cleaning.
Successful joint preparation steps include:
1. Two-rag method of cleaning:
Use lint-free rags.
First rag has solvent poured on it, not dipped in solvent.
Second rag removes solvent and contaminants.
Change rags often.
2. Form-release agents, oils, paints, and old waterproofing materials must be removed by
mechanical means, followed by recleaning joints, including pressure-washing if necessary.
3. Joint sides must be dry and free of moisture or frost.
4. Loose joint sides must be chipped away and cut smooth. Jagged edges may cause air
pockets to develop during sealant installation.

Priming
Primers are used to ensure adhesion between sealants and substrates. If there is any doubt
if a primer is required or not, adhesive tests should be completed with and without primers
to determine the most successful application methods.
Using too much primer, allowing primer to cure too long before installation, or apply-
ing sealants over wet primer will cause sealant failures. Manufacturer’s application
instructions pertaining to mixing, coverage rates, drying time, and application time vary
with different types of sealant and primers. Instructions must be consulted on an individ-
ual basis for proper installation, including:
● Use of proper primer
● No overapplication of primer
● Priming within application time recommendations
● Discarding of primers that are contaminated
● Manufacturer’s recommendations
Figure 5.34 shows the correct method of installing primer in a joint.

Backing materials
Backer rod and backing tape prevent three-sided adhesion in joint design. Tapes are used
where a firm substrate, against which to seal, exists at backs of joints, when joints have
insufficient depth for backer-rod installation. Rod is installed in joints where there is no
backing substrate. The backer rod or backing tape provides a surface against which to tool
material and maintain proper depth ratios.
Failure to install backer rod properly causes cohesive failure due to improper sealant
width-to-depth ratio (Fig. 5.35). Backer-rod depth must be kept constant, which requires
use of a packing tool (Fig. 5.36). This simple tool, a roller that can be adjusted to various
depths, is unfortunately rarely used.