QUESTION: Please advise us on the following problem. Our ceramic tiles above the bathtub have been leaking and we are going to have to remove them and replace the wallboard. There is mould behind the tiles because there are black areas in the basement ceiling and main floor floorboards where the pipes come through.
What disinfectant should we use to kill the mould after we open up the wallboard? Is bleach safe to use and in what proportion to water? What precautions should we take when removing the wallboard?
Thank you for your attention to this matter.
Elizabeth & Stephen Bahr
ANSWER: Moisture damage in bathroom walls is one of the main things I check for when inspecting the interiors of homes because of the high cost of repairs associated with this very common defect. This issue can be quite insidious as evidence of a major problem may be hidden from view to the average homeowner.
I am consistently telling my clients during pre-purchase home inspections to repair or replace the silicone caulking around tubs and showers and maintain grout in tile walls. While these may seem like minor repairs and hardly worth the effort to identify, they can be instrumental in preventing the issue you are facing.
Ceramic tiles are an excellent product for preventing moisture damage to the area above your tub, but they are only as effective as the condition of these two items. Mortar between the tiles will last for many years but once it becomes eroded or deteriorated, it can allow moisture to infiltrate the backing behind the tiles.
Even more important, silicone caulking at the joint between the tub and tile and in corners has a very limited life expectancy and should be removed and replaced every one or two years. If either of these two areas are neglected it may not be long before moisture damage behind the tile leads to major repairs to the entire shower area.
One reason this is such a common issue is the backing material used behind the tiles. Often, this is not moisture-resistant enough to last a long time in the wet environment of your bathroom. Many homes have simple plaster or gypsum drywall behind these areas that will easily absorb moisture from the shower. Even moisture-resistant drywall will have a limited life expectancy in this application.
More modern homes, or older bathrooms upgraded by knowledgeable contractors, should have more moisture-resistant backing for tiles. Cement-based sheathing or protective plastic membranes are often employed behind tiles to keep the substrate solid even if some moisture does penetrate the tile surface. After you remove the damaged material in your shower, ensure you are employing one of these better products to prevent a reoccurrence of your current situation.
Now that I've offered my advice on how to proceed with the new surface after replacement of your old shower area, I should answer your question. The repairs or treatment of the moisture damaged, mouldy or rotten material behind the tiles depends largely on the extent of the damage.
If you remove the tiles and wall covering behind them and find only stains on the studs, there may be little you need to do before redoing the bathroom. If you find large stains or blackened or soft sections to the wood framing then you will have to do more significant remediation.
The way to simply test the framing is to take a sharp tool such as a scratch awl or screwdriver and firmly push it on the surface of the wood. If the tool does not easily penetrate the surface, the wood should have minimal damage and maintain its structural integrity. If the sharp surface of the probe easily punctures the wood and sinks in more than a few millimetres, the wood will need to be replaced. There is no treatment that can prevent further deterioration to wood once significant rot has taken hold and only removal will do.
Your concern with mould in this area will likely be concentrated in two areas, the wall covering and the wood framing behind. Since you will have to remove and discard the wall coverings completely to do a proper assessment and repair, there is little issue there. Once this is removed from your home there will be little chance of any mould in this material being a problem after cleanup and repairs are complete.
If the wood is in good condition behind this area and you are still concerned about mould, I would not recommend using any bleach for treatment. Chlorine bleach is a toxic substance and if you mix potentially hazardous types of moulds with it you could create more dangerous toxins that have unknown effects. There are commercially produced liquid fungicides designed for this purpose that could be applied to the surface of the studs, which are available at home centres or other suppliers.
What you should understand is there are naturally occurring moulds everywhere in our environment, indoors and outdoors. Wood rot is a type of mould, but is not one known to cause health concerns to people. Finding a small amount of surface rot in wood framing behind a damaged bathroom wall or in the old floor boards below the tub is not cause for panic.
If the material is badly damaged, cut it out and replace it after tearing out the tiled walls. If the wood has a minor amount of surface staining or damage, it should not become a major issue and certainly not a health issue as long as the walls are properly repaired with the right materials and well maintained in the future.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors - Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca
trainedeye@iname.com
