Proper Shower Construction

September 6, 2005

   After many years as a forensic tile consultant, involved with inspection and documentation of failures in all types of residential showers, I’ve seen clear evidence that virtually all shower assemblies are leaking into structures, with resulting structural damage and mold issues. This is a product of untrained contractors, absence of proper construction details, and a basic misunderstanding – or lack of understanding – of the shower environment and design specifications/details.
   Architects, specification writers, contractors, inspectors and consultants are often concerned with only two areas in a building’s envelope relative to water entry: roofs and windows. Very little, if any, attention goes to showers or baths. The real truth is that a shower, used once a day for 12 minutes, will experience between 2.2-414 times more water in one year than the roof of a house … no matter if the dwelling’s in a rain forest or desert.
   For years, we’ve built shower walls and receptors out of mortar because it’s basically unaffected by moisture/water. This works well, except when moisture gets into the mortar; the moisture becomes impossible to control, and can migrate into substrate materials instead of the drain.
   To prevent this, the shower assembly must be built as a “water-management system” that controls and directs all water/moisture to the drain. Any moisture migrating into the system must be directed to the drain.
   Leaking shower assemblies cause mold and structural damage. The big question everyone asks is: Why is mold such a big issue now when we didn’t have a problem before?
   The answer is fairly simple; building materials have changed, and aren’t as tolerant to moisture as previous materials (OSB, particle-board, MDF, organic adhesives, drywall, etc) and buildings are tighter for more energy efficiency. We’ve also changed the type of general construction materials from stone/concrete, to drywall/wood framing or drywall and medium-density fiberboard (MDF) with steel studs.
   The reduction of moisture tolerance of the building followed, from about 500 gallons down to about five gallons (according to Joe Lstiburek of Building Science Corp.). Building materials handle a certain amount of moisture; however, when that amount is exceeded, the excess is available to support mold growth.
   For these reasons, it is vitally important that we become aware of all areas of construction relative to a shower assembly and the necessity to eliminate any possibility of moisture leaks.
   Additional problems also show up when using natural-stone products, as opposed to ceramic tile, in that the stone/marble is typically more-porous and leads to staining and efflorescence due to excessive water build-up in the mortar beds or spotting mud.
   Today, newer materials are currently being marketed for their ability to reduce mold. Many of these are basically the same products with the addition of anti-microbial additives. While these additives may reduce microbial growth for a period of time, the structural damage (swelling substrates, etc,) due to moisture intrusion is expected to be the same and therefore the need to control and manage water in the assembly has not changed.

ON EVERY JOB …
   Here are some common-sense items to review and inspect:
   Always remember: Showers are a water-management system.
   • All horizontal surfaces must slope to drain.
   • Horizontal waterproof membranes must slope to drain a minimum of 1/4” per foot on areas such as seats/benches, shampoo shelves, windowsills and pony walls. The curb/dam should be sloped a minimum of 1/4” per 3 1/2” toward the drain.
   • Tub corners must slope to drain or the tub needs to be reset or rejected.
   • Framing needs to be square and true to plane.
   • Walls must be furred out to meet tub or shower receptor flanges.
   • Any tub used as a shower receptor must have the required 1”-high integral flange.
   • Tubs and fiberglass pans need to be properly supported to eliminate movement or flexing during use.
   • Tile-lined mortar-bed shower receptors require open weep holes in the shower-drain assembly. These must be protected with pea gravel prior to installation of the dry-pack mortar bed.
   • Dry-pack mortar used for a tile-lined shower receptor must use an anti-hydro additive, or equal type product, in the water to insure an open bed.
   • Water must be able to flow through the receptor float in order to get to an open weep hole! The receptor mortar bed must be tested prior to installation of the finish surface material to ensure proper operation and management of the moisture migrating into the mortar bed. The weep holes must work, or be repaired, prior to setting tile on the receptor surface.

REMEMBER THE BASE
   Manufacturers continue to develop new and improved products for shower construction. However, the improved products won’t be of any benefit if the base construction is wrong, and moisture is allowed to migrate everywhere except toward the drain.
   Shower construction evolved over the years, with contractors modifying various types of wall-construction methods in order to speed up production – while companies developed newer materials to help speed production and also trying to stop the leaks. Unfortunately, contractors often perform little or no research when modifying construction methods or materials
   There is a danger with the newer materials giving the contractors the sense of a safety margin and therefore relaxing the quality control and attention to details, because the materials will do the job even if they get a little wet. In other words, the attitude has been, and still is: “I’ve been doing this for 20/30 years and I’ve never had a problem.”
   Today however, we’re all faced with the fact that insurance companies have excluded all claims for mold issues from their coverage, regardless if it’s your car, house or business. That leaves the contractors directly responsible for mold-related damages and the industry (as a whole) hasn’t done an adequate job in understanding the water-management system of shower assemblies or provided proper training. It’s time for contractors to ask themselves if they can afford the risk of modifying construction methods and materials, or improperly building a shower assembly.
   It’s extremely important to build the shower assembly with equal or better care than the roof of a house. Roofs are not built with negative slopes for obvious reasons – so why build them into a shower assembly?
   Don Halverson works as a forensic tile consultant, based in Thousand Oaks, Calif. He’s a Ceramic Tile Consultant (CTC) – Ceramic Tile Institute of America, a Ceramic Tile Advisor (CTA) – Ceramic Tile Institute of Northern California, board-certified Microbial Remediation Supervisor (CMRS) – American Indoor Air Quality Council, Certified Residential Mold Inspector (CRMI) – Indoor Environmental Standards Organization (IESO), and a member of the Marble Institute of America (MIA).