Page 277 - Construction Waterproofing Handbook

5.36 CHAPTER FIVE

FIGURE 5.32 Exposed aggregate precast joint problems.

This roughens their surface before sealant application. This rough surface may provide an
acceptable substrate for sealants such as butyl or silicones, but PVC materials should never
be used at high-movement joint areas.

Stonework
Building facades of limestone, marble, or granite generally provide a surface acceptable for
sealants. However, adhesion tests should be completed to determine their acceptability,
since there are so many finishes of each natural stone type available. Priming is usually
required with these types of substrates.
It is important to note that in most cases a primer or uncured sealant may stain stone
work. Therefore, precautions including masking joint faces before sealant or primer appli-
cation will prevent staining. With porous absorptive stone, closed-cell backing material
should be used to prevent backing from absorbing water that passes through the stone
facade.

Terra cotta
Terra cotta tiles or stones manufactured from natural clay are typically supplied with a
baked or glazed surface finish. However, sides of the tile are typically unfinished clay and
are very porous and absorptive. Primers are required for adequate sealant bonding.
Should the facing of terra cotta be porous, water absorption may cause adhesion prob-
lems or gassing of sealants. Closed-cell backing materials should be used to prevent the
backing from absorbing water entering through the terra cotta facade.

SEALANT APPLICATION

Of all factors affecting sealant performance, installation is the most critical and most often
causes joint failures. No matter how good a sealant is selected and how well a joint is