Sewer Gas Odor Can Waft Through Incorrectly Installed Toilet Gasket

Odors, vermin and water can get through the joint between the toilet and the drain pipe if the toilet gasket doesn't make positive contact.
Odors, vermin and water can get through the joint between the toilet and the drain pipe if the toilet gasket doesn't make positive contact. (By Tim Carter)
By Tim Carter
Saturday, January 10, 2009

Q: DEAR TIM: My husband installed a new gasket on the toilet in our master bathroom as part of adding a new ceramic tile floor. He's pretty handy, but I soon noticed a sewer gas odor in this room. There wasn't an odor before. He can't smell it, and I'm reluctant to have him do the job over. The toilet doesn't move and the caulking is perfect, so I can't imagine where the odor is coming from. What needs to be done to correct this? -- Vikki H., Henderson, Ky.

A: DEAR VIKKI: The toilet bowl gasket was not installed correctly. The smoking gun is the fact that no odors were present before your well-intentioned husband started the bathroom remodeling job. I'm afraid that he will need to start over, but we need to discover what he did wrong so this second attempt gets it right.

The source of the odor is probably the holes where the toilet bolts pass through the ceramic toilet bowl base, which are usually not sealed. The sewer gas that's wafting past the toilet wax gasket can easily seep past the bolts and the decorative caps. The caulking between the base of the toilet bowl and the floor won't stop the odor if these bolt slots are unsealed.

The seal between the toilet flange -- the transition fitting that allows you to connect the toilet to the drain piping -- and the toilet bowl is critical. Not only odors, but also vermin and water can get through this joint if the toilet gasket is not making positive contact.

When replacing a toilet gasket, you need to pay close attention to many details. Homeowners and some rookie plumbers fail to look at the recessed area under a toilet bowl. This part of the toilet is often about three-quarters of an inch deep. This distance is measured between the bottom of the toilet bowl (i.e., where it contacts the finished floor) and the underside of the unglazed porcelain outlet where the wastewater exits the toilet.

The next thing you should pay attention to is the thickness of the toilet wax gasket. Most of them are no more than seven-eighths of an inch thick. I've measured many, and some are just three-quarters of an inch thick.

For a toilet gasket to seal properly, the space between the underside of the unglazed fixture, where the water exits the toilet, and the top of the toilet flange should be no more than a half an inch. This means the top surface of the toilet flange should be at least a quarter of an inch above the finished floor surface. The top of the flange should be level, and the flange must be secured to the floor so it doesn't move.

It's possible that your husband wasn't aware of this important point. The top of the toilet flange may have been flush with the floor or even sticking up too high. I've seen toilet flanges installed by inexperienced plumbers and homeowners that were an inch or more above the finished floor. When a toilet flange is too high, a poor seal can result because all of the wax gets squeezed out between the toilet and the flange as the toilet is secured to the flange.

In your case, I think an autopsy will reveal that the toilet flange got buried by your new flooring. This is a very common mistake. A homeowner may install ceramic tile in place of a sheet vinyl floor. By the time ceramic backer board is put down and the new tile laid, the top of the toilet flange can be well below the finished surface of the floor. When this happens, it's entirely possible the toilet gasket never even touches either the flange or the underside of the toilet bowl.

Be sure your husband removes the toilet and discards the gasket he just installed. Clean the surface of the toilet flange as well as the underside of the toilet bowl. If the flange is not sticking up a quarter of an inch above the surface of the ceramic tile, you can add an extender or use multiple toilet gaskets to achieve the seal. If you use an extender to create a new flange height, be absolutely certain the gap between the existing flange and the extender is sealed with a code-approved sealant. Failure to do this could create both water and sewer gas leaks again.

Tim Carter can be contacted via his Web site, www.askthebuilder.com/printer_Submit_Question.shtml.

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