Secrets of the failed stucco, revealed

Joseph Ponessa had some thoughts about stucco that I wanted to share with you.

Ponessa is professor emeritus of housing, indoor environment, and health at Rutgers Cooperative Extension.

He got in touch after I wrote an article about a lawsuit by the Commonwealth of Pennsylvania against an area developer over stucco issues with new homes.

I had mentioned EIFS - Exterior Insulation and Finish System - which had been widely used in the 1990s and early 2000s but was the source of major lawsuits over poor installation - failure to follow manufacturer's instructions - resulting in mold and mildew problems.

Ponessa said research conducted mainly by Building Science Corp. in Massachusetts in the late 1990s identified the causes of EIFS failures.

Though traditional cement-based, three-coat stucco systems have been used successfully in both wet and dry climates for many years, the more modern, synthetic two-coat products are not as durable, he said.

The inevitable cracking or poor detailing around penetrations has allowed water intrusion, which is disastrous in wet climates, Ponessa said.

The other issue involves synthetic stucco's interaction with underlying water barriers.

Research at Building Science Corp. revealed that, unlike cement-based stucco, the synthetic formulation interacts with water barriers - building paper, felt, or housewrap - to destroy their water-repellent properties. Water coming through the stucco penetrates and enters the wall cavity.

The solution that researchers identified is simple: Use a second, "sacrificial" layer beneath the stucco.

That can even be cheap building paper, Ponessa said. The double layer solves the main problem.

"There are a few more details and caveats, but this is the essence of the problem," he said.

It's an old story.

EIFS had been used successfully in commercial applications since the 1950s, but it was cheaper than the old three-coat system and, well, you know what happened.

Remember what I always say about reading directions.

aheavens@phillynews.com or write him at Box 8263, Philadelphia 19101. Volume prohibits individual replies.