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Home Improvement--General/Plaster walls bubbling in bathroom


Bubbling plaster
Bubbling plaster  

Bubbling plaster 2
Bubbling plaster 2  
We moved into this house 4 yrs ago. We replaced the bath exhaust fan immediately with a Panasonic. It was attached in the existing manor. The tube runs across the attic floor for maube 10 feet and slants up and out the existing hole in the side of the house. I realize it should go straight up. It does work alright although it could be better. Soon after I noticed the plaster bubbling up in random places on the wall. My husband thinks there must be a leak in the attic and therefore moisture being inside and working its way out. I think it must be moisture on the air working its way in. We can find nothing to support either theory. There is no sign of moisture in the attic and the roof is 5 yrs old. There is a window and it has been left open at times as well as the bathroom door diring showers nothing seems to make a difference. The bubbling seems to be random. The places do spread but aren't really connected to each other. We have no clue what this is. We have both lived on homes without any exhaust fans and have seen moisture be an issue in expected ways like mold perhaps but never this. We need advice please :) I can supply more pics

Hello, Annette.

Water leakage is one of the worst problems to diagnose, because water chooses the path of least resistance, which may not be obvious without serious investigation.  

I'm understanding that the new Panasonic exhaust fan was connected to the existing duct, then you started having problems. Something happened during the installation that caused the problem. Your pictures show more serious problems than condensation build-up inside the duct. You have a serious leak problem. My theory is that water is wicking from the outside, using the duct to lead the water onto your bathroom ceiling.

My recommendation is to hire a contractor who will do a water test (preferably when it's not raining), to see whether the water is flowing (being directed) by the duct from the termination point. I've witnessed similar investigations; it requires communication between at least three people: Someone outside with a hose, someone in the attic (to see and hear water), and someone in the bathroom who can report when the water appears (or a new bubble appears. Once the problem is diagnosed, you'll probably have to reinstall the duct, and have the plaster repaired/repainted. You should get a written warranty for the repair work, so you don't have to keep paying if the repair doesn't last, or the problem recurs.

Your idea of having the duct terminate vertically is excellent, but I wonder why the duct wasn't installed that way originally. Air flow is restricted by the overall length, plus the number of bends in the duct. It's in your best interest to have as much air flow as possible, to eliminate moisture from your bathroom that can lead to mildew and mold.

Wishing you the best of luck, finding and fixing this perplexing problem.


Diane Plesset, CMKBD, C.A.P.S., NCIDQ
D. P. Design  

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Diane Plesset


I will answer questions about anything to do with bathroom remodeling: design considerations, safety, function, materials (cabinets, countertops, plumbing fixtures and fittings, lighting/switching, heating and ventilation, tile, stone, concrete, tub and shower enclosures, flooring, etc.), saving water, trends, ROI, and appearance.


25+ years as a bath-kitchen design specialist, hundreds of completed bathroom projects (all styles, all investment ranges). Author of "THE Survival Guide: Home Remodeling," co-host of a home improvement program on a local radio station for over three years. Currently hosting "Today's Home" on Lifestyle WebRadio every Sunday afternoon (

NKBA (National Kitchen and Bath Association), NAHB (National Association of Home Builders), PRO (Portland Remodelers' Organization), IDPC (Interior Design Protection Council).

"THE Survival Guide: Home Remodeling" (my book, published in 2003), Designers' Illustrated Magazine, Gentry Magazine, Kitchen-Bath Business Magazine, Kitchen-Bath Design News Magazine,Interior Coordinator Magazine (Japan); San Jose Mercury News, San Mateo Times, San Francisco Chronicle, Statesman Journal, Portland Tribune, Oregonian.

Multiple degrees: Bathroom Design, Residential Interior Design, Kitchen Design, and Lighting Design. Regularly attend classes and seminars to maintain current knowledge about codes, trends, sustainability, new products, etc.

Awards and Honors
Awards: Henry Adams Designer of the Year, CoTY, Master Design, Best of the Best, Chrysalis, Excellence (best home in its category), and NABE (best how-to book, 2003). "THE Survival Guide: Home Remodeling" received #1 listing in the City of Chicago publication, "Hiring The Pros".

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To see photos of completed projects, visit my website:

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