By: Herb Nordmeyer
We hear a lot of talk about one-coat stucco. It is less expensive than three-coat stucco. But is it as good as three-coat stucco? The answer is a definite “Maybe.” Then the serious question is asked, How can I achieve a quality one-coat stucco job?
One-coat stucco’s are not listed in the International Building Code or in other building codes, but are authorized by evaluation reports. If a one-coat stucco does not have an evaluation report issued by an official evaluation service, then it cannot be used where code-approved three-coat stucco is specified. Obtaining an evaluation report is not cheap. Often up to $100,000 is spent on testing before the report is issued. The evaluation report is a statement by code engineers that they have studied testing data and that the product being rated meets the intent of the code if it is used in a specific manner. If a one-coat stucco is going to be used on the house that you are having built, you should ask the contractor for a copy of the evaluation report. After you have read the report, ask the contractor to explain different parts of the evaluation report. When I read an evaluation report, the word obfuscate comes unbidden into my mind. There is no intent to obfuscate, but the engineers have tried to cover all eventualities with precise language.
If a one-coat stucco is applied according to the terms of the evaluation report, a user can assume that it will function as well as a three-coat stucco will function. Sometimes, in order to save money, or because the applicator has not carefully studied the terms of the evaluation report, an applicator may not follow all of the terms of the evaluation report. In such cases, problems can develop. By having the contractor explain the report to you, you are ensuring that s/he has read the report. By showing an interest, the contractor knows that you are monitoring the job, so s/he will ensure that the crew is more diligent than they otherwise might be.
Many failures occur around window penetrations when adequate care is not used to join two dissimilar materials. Insist that the window opening be wrapped according to the window manufacturer’s instructions and that after the stucco is applied the interface between the window and the stucco be sealed with backer rod and a good quality sealant, not a $0.79 tube caulk.
The evaluation reports do not specify the top coating for one-coat stuccos. All stuccos need to be protected. Some applicators have mistakenly assumed that a diluted coating of latex paint provides adequate protection. This is not the case. Most one-coat stuccos need to cure for at least seven days, and some for as long as 28 days, before an acrylic finish coat will permanently bond to them. Don’t rush the contractor. By delaying, he is giving you a permanent finish. Most one-coat manufacturers have a warranty program that is tied to using one or more of the finish coats that they produce. If the one-coat stucco that your contractor has selected does not have a manufacturer-furnished finish coat, then as a minimum, it should be finish coated with two coats of elastomeric paint for a total dry thickness of 12-mil. An acrylic texture coat is an acceptable substitute.
Get involved, so your contractor knows that you are interested in a quality job and that you and he both understand what the evaluation report requires. Then you can expect to obtain a quality job.
Herb Nordmeyer, author of The Stucco Book-The Basics