COLUMN BUILDING SCIENCES
flooring failures. We get it in roofing failures and deck
failures with cold fluid applied waterproofing installed
over concrete decks and concrete roofs. We get it in coating failures. Now we are getting it with thin real stone
and the thin manufactured stone veneer.
This is becoming a huge issue. The solution is easy: a
drained vented cavity behind the thin set mortar and
stucco. Sound familiar? Need to drain the rain baby, and
dry the layers. Go back to Figure 1. The approach in Figure 1
addresses both the rot problem and the thin stone adhesion problem. We get a two-for-one.
Further note. We are getting good at understanding
highly alkaline environments. Polymer modification
today is not the same as polymer modification yesterday.
Are some modified thin sets better than others? Yes, but
not enough to eliminate the gap to stay out of trouble.
The lessons of the floor tile failures lead to a change in
tile flooring practices. We are going through similar
changes with thin veneers.
Think about the big picture. We need gaps behind
claddings; we need gaps behind rigid insulation; we
Precision Discharge Air Control
with the Rawal APR-E® Valve
Control any single or 2-stage DX system to a precise discharge
air setpoint with our electrically driven & electronically
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unloader for aftermarket installations. The APR-E™ provides
modulation for any DX air-conditioning system and is easily
integrated into an existing BAS/BMS or with a stand-alone
controller for New or Retrofit Systems.
FIGURE 2 Osmosis. There is salt in stone. You could argue that stone is really solid
salt. Second Law of Thermodynamics wants to get into the stone to dilute the concentration of salt that becomes a solute.
Stucco Layer
Osmotic Force
"Thin Set" Mortar
Coating on Backside of Manufactured
Stone Veneer
Osmotic Force
Manufactured Stone Veneer
FIGURE 3 Capillary Break Under Rigid Insulation. The gap under the rigid insulation
prevents the rigid insulation from becoming saturated and promotes drying.
Ballast (Rock, Pavers, Earth)
Filter Fabric
Extruded Polystyrene Insulation
Sloped Concrete Topping; Slope
Minimum 2% to Drains
E
OBTAIN THY
FLEXIBILIT D
LE
IL
CH
OF A
STEM
WATER SYA
ON
ET!
DX BUDG
Concrete Structural Deck
Drainage Gap, i.e., Drainage Mat or
Grooved Insulation
Fully Adhered Roof Membrane
* Dew Point Control for
critical environments
* Applicable to any
VAV/MUA/DOAS systems
* Reset DAT to minimize
reheat for energy savings
RAWAL DEVICES, INC. | PHONE: 800.727.6447
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ASHRAE JOURNAL
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need gaps under protected membrane roof insulation
and green roofs (Figure 3); we need gaps under slabs
("capillary breaks"); we need gaps almost everywhere.II
It did not used to be this way. We changed materials,
energy flow and moisture flow. To compensate we need
to give back some energy. There is no such thing as a free
thermodynamic lunch.
IILauren
Hutton hygric redistribution.
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