Underperforming Stucco

Don Procter

September 2005

In the province of Alberta where two-coat stucco systems are still commonly applied on homes in new residential subdivisions, the Alberta Home Builders Association and other building groups are setting up a quality assurance program to improve the way things are done. And for good reason. Tests conducted on water penetration and serviceability of two- and three-coat exterior stucco systems applied over the last 10 years to 47 homes in Calgary and Edmonton indicated that most are underperforming. Furthermore, many aren’t even code compliant.

The lab and field tests were conducted by Morrison Hershfield Limited.

"From the conclusions we decided that we needed to do something about workmanship in Alberta,” points out Joan Maisonneuve, technical liaison, Alberta Housing Industry Technical Committee. The AHITC was formed by the Alberta Home Builders Association and the Alberta New Home Warranty Program to resolve technical issues in the residential building industry.

The Alberta Wall & Ceiling Bureau is involved in the stucco liaison committee, which aims to educate both stucco applicators and home builders on the application process. It includes a list of standard specifications, inspections at various stages of the work plus a series of educational workshops on stucco installation geared to builders and applicators. There will also be a stucco certification course for applicators covering stucco system substrates, paper and wire, application and curing.

"There is a labor shortage and a lack of formalized training in this area. We want the stuccoers to become much better educated. Our objective with builders is to make them informed consumers, not stucco experts,” Maisonneuve says.

At this juncture the QAP is an important beginning to develop a permanent educational program for stuccoers and builders and also a starting place to build rapport between the two groups, she points out. "We expect to see changes for the better from the work in the short term, but to have a real impact down the road there will have to be a long-term educational program for both site supervisors and stuccoers.”

What predicated the testing was a request by stucco applicators and builders to relax the code requirements, allowing for a thinner two-coat stucco system, says Bill Brown, senior building science specialist, of Ottawa-based Morrison Hershfield.

A two-coat system meets the Alberta Building Code as long as it meets the same 19 millimeter (3/4 inch) criteria required for three-coat systems under the National Building Code. The problem is that the stucco industry has been moving to a thinner pre-mix, pre-colored topcoat. To meet that 19 millimeter (3/4 inch) thickness, it requires a base coat of about 5/8-inch thick, which is prone to sag during setup.

Stucco was king in Alberta’s fast-growing oil cities from the 1960s until the 1980s when the less expensive vinyl took the lead. Problems with workmanship probably grew over the next couple of decades as many retiring stucco craftsmen were replaced by inexperienced applicators facing increased pressure from builders to meet fast-paced construction schedules in booming Edmonton and Calgary.

Adding to the problem, is that there are no physical tests for the performance of stucco, points out Brown. "There are just prescriptive requirements for manufacturing it.”

Morrison Hershfield’s field assessments on 23 homes in Edmonton and 24 in Calgary included cracking, spalling and efflorescence. The company also made thickness measurements and strength tests. All the homes are between three and 10 years old. The assessments were complicated by the fact that many stucco applicators use the double-back method, from which it is difficult to determine if a wall is two-coat or three-coat from core samples.

About the Author
Don Procter is a free-lance writer in Ontario, Canada.