Mildew in the Greenhouse

House Doctor | Gary Dymski

August 1, 2002

Q. I just can't seem to solve this problem. We have an indoor greenhouse that came with our home when we bought it. The greenhouse is built on a brick foundation, and inside is a hot tub that I think is causing the problem. Because of moisture from the hot tub, there is a mildew buildup on the bricks. We have tried power washing, a commercial brick cleaner, chlorine bleach and several other products without any success. Got any ideas?

-Thomas Heath,

Cold Spring Harbor

A. Here are two more products to try: oxygen bleach and SIMPLE WASH. Oxygen bleach is a powdered cleaner available at home centers, hardware stores and department stores. One of the more popular brands is OxiClean. Using the scooper you find in the OxiClean bucket, mix about 5 scoops to a gallon of hot water. Pour the solution on the brick and scrub with a nylon-bristle brush. Let the solution sit for about 20 minutes before rinsing with cool water. Repeat if necessary.

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SIMPLE WASH is a cleaner and brightner made by BIO-WASH, a Canadian company that specializes in cleaning products used by contractors. It is supposed to be especially good at cleaning mildew from outdoor surfaces, including concrete and brick.

You can get SIMPLE WASH, which is applied with a pressure sprayer, for about $13 a gallon at the Janovic Plaza Paint Store in Long Island City (718-392- 3999). Janovic also has a store in Seaford (516-785-0332), but when I called, the Seaford store did not have SIMPLE WASH in stock. You can get more information on the cleaner and other BIO-WASH products at www.biowash.com or by calling the company at 800-663-9274.

No matter what you use to clean the mildew, I have a feeling it's going to be a recurring problem. First, your greenhouse has hot, humid conditions, and there's a moisture buildup at the base of the tub. Installing a bathroom- or kitchen-style electric fan to vent some of this moisture could help. When the tub is in use and the water is hot, run the fan to remove moisture from the greenhouse.