Civil Engineering Reference
In-Depth Information
results in structural failure of masonry veneer.
No matter what the cause, a failing masonry mall is difficult to
address and it can almost never be repaired well enough for continued
satisfactory performance. The ultimate method of dealing with a failing
masonry wall is to remove the masonry material, including the existing
flashing, etc., and correctly install new. However, this is an expensive un-
dertaking and there are alternatives.
Clear water-repellent coatings are sometimes recommended to re-
duce water absorption and reduce the amount of water that penetrates
the exterior brick masonry. However, clear water repellents can seldom
stop water penetration through cracks over 0.02 in. in size. Clear water re-
pellents cannot stop water penetration through incompletely filled mor-
tar joints or from sources such as ineffective sills, caps or copings. Their
effectiveness under conditions of wind-driven rain is questionable.
Asa
result,theuseofclearwaterrepellentcoatingstoeliminatewaterpenetrationin
awallwithexistingdefectsisoftenfutile.
Steel panels, using pre-finished single thickness formed sections,
have successfully been applied over existing masonry walls that were
performing poorly, Panels are installed on hat channels and serve as rain
barriers to eliminate the direct impingement of blowing rain onto the ma-
sonry. This approach can be a low cost, though limited life, solution to
leaky masonry wall problems.
A short-term (5- to 10-year) solution to deteriorating or poorly de-
signed or construction masonry walls is to apply an elastomeric acrylic or
silicone masonry coating. These opaque coatings, with an applied thick-
ness of 8-12 mils (about 50-100 sq. feet/gallon), are applied by rolling or
spraying to form a flexible, textured or smooth finish. Elastomeric wall
coatings are formulated to stretch and bridge cracks (assuming proper
crack preparation and sealing) that may form due to movement. When
the wall contracts as temperatures drop and the cracks expand, the elasto-
meric wall coating stretches and resists cracking itself. When the tempera-
ture rises and the cracks become smaller, the coating returns to its original
shape without wrinkling or leaving ridges. This crack bridging capability
results in a long lasting, uniform finish.
To achieve the balance of properties required to make a top quality
elastomeric wall coating, manufacturers use acrylic binders that are de-
signed specifically for this use. Using these acrylic binders provides the
coating with a high degree of flexibility and elasticity, while exhibiting
appropriate tensile strength, and superior alkali resistance and dirt resis-
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