Plugged weeps
The second common drainage problem this author sees involves plugged weep holes. Industry standards state the weeps are to be covered with pea gravel or with a plastic protector to ensure the holes stay open. Often, this weep protection is left out, and the mortar is placed over top the holes, plugging them. Thus, if the waterproof membrane is properly sloped to drain, the water cannot escape into the drain. Again, this leads to musky odors, wet appearance, or stone spalling and staining, as previously noted.
In some instances, both the weep holes are plugged and the membrane is not properly sloped to drain. A good example of multiple compounding deficiencies is an exterior deck this author investigated that had a natural stone on its surface. The stone had badly spalled in some areas after a few years of use. An intrusive inspection of the tile assembly revealed it had a primary waterproof membrane under a drainage mat that was below a mortar bed to which the stone was attached.
Not only were the weep holes plugged, but when water was poured over the membrane where a stone had been removed, it flowed away from the drain, despite being only 305 mm (12 in.) away. A hose was run for 15 minutes and the water never reached the drain—the waterproof membrane was clearly not properly sloped. Essentially, there was a reservoir of water stored under the stone installation, replenished by rain and weekly deck maintenance. This constant and excessive exposure to moisture migration resulted in the stone becoming badly spalled and stained.
Spalling is typically caused by moisture migrating from the stone’s underlying substrate up through to its surface where the moisture evaporates. As the moisture travels from under the stone through the cementitious materials, and through the stone itself, the moisture picks up various minerals (i.e. salts) that dissolve in the moisture. When the moisture reaches the stone’s surface, it evaporates—the minerals precipitate into solids again. This expansion or crystallization of the mineral, referred to as efflorescence, causes the surface of stones to deteriorate to some degree. With constant cycles of evaporation of moisture at the surface, this can badly deteriorate and/or stain the stone.
Incomplete waterproofing or vapor retarders
In some projects, waterproofing or vapor retarders are not complete or continuous; they tend to lack flashing at transition areas. Considering the potential collateral damages a defective balcony can incur, it is important to construct it like a big shower pan. Assuming the deck has been properly pre-sloped, the waterproof membrane must continue, or be flashed, up the wall at least 76 mm (3 in.) above any thresholds to prevent water from causing any potential collateral damages.
All seams and transitions must be properly sealed or flashed. These are the areas most vulnerable to problems, so they need extra attention to ensure they are correctly installed. All penetrations must be properly waterproofed, flashed, and sealed with a sealant. The waterproof membrane should never be penetrated, unless it is unavoidable, and then the penetration has to be properly flashed and sealed with the appropriate sealants to ensure it never leaks.
When the decks have drains, they should be strategically placed to not only allow for adequate drainage, but also to make sure the selected tile can manage the various slope transitions. For example, larger tiles are limited in accommodating slopes and transitions than smaller units.
This author often finds decks are sloped to the outer edge without any type of gutter or drain. The water drains over the side of the balcony and eventually results in staining along the stucco, or staining and spalling the stone siding.
The latest trend is to use trench or lineal drains that can be installed at the perimeters of decks or showers. The trench drains can be installed so the tile or stone is attached to the center, enabling it to blend within the flooring and allowing drainage around the tile edges. There are gutters designed for tile that can be installed at the perimeter edges of decks so the water runoff can be controlled and directed into drains. It is never a good idea to let water runoff the edge of decks. Water should always be directed into drains or scuppers connected to irrigation drainage.
Another big issue in terms of the lack of continuous moisture or vapor barriers and flashing is with on-grade slabs. ASTM E1643, Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs, states the vapor retarder is to continue from under the slab and up the sides of the slab and footings. This is the only way to keep moisture from the landscape soil to migrate laterally into the slab on the exterior decks as well as migrating into the interior areas of the slab.
Some pool decks do not have a vapor retarder; others do, but typically do not continue up the sides of the slab. In either case, the landscaping may be butted up to the slab edge, and even the stone edge. This allows the water full of minerals from the soil to migrate ultimately into the stone surface, resulting in spalling, staining, and other potential problems.
In terms of regular showers and steam rooms/showers, continuous waterproof membranes and flashing are critical. Shower tubs and shower pan receptors should be waterproofed and flashed with the wall vapor retarders to provide a continuous path for water to reach the drains.
