Q. We live in a downtown condo built in 2004 and have marble floors in our bathrooms. All of the toilets had a brownish stain around the base. Why is this happening?

RONNA FRIED

A. Although I’m not a plumber, I have seen this before and can offer advice. It’s probably a leak, one that can damage the subfloor under the marble, loosen the tile, and stain the ceilings below the toilet.

Check to see whether the toilet is loose. Grab the bowl and try rocking it side to side. If it is loose, there is a good chance that the wax ring is no longer providing the proper seal. Tightening the T-bolts on either side of the toilet base may help, but be careful not to overdo it. They are connected to the toilet flange and compress a wax ring between the flange and the base of the toilet, forming a watertight seal. The wax ring can become deformed, and if overcompressed or damaged, it can leak.

If that does not solve the problem, replacing the wax ring is the next logical step. A failed wax ring will definitely cause a toilet to leak at the base. Replacement is an easy, low-cost repair.

Q. Water condenses on the underside of my metal Bilco hatch door and drips onto my concrete stairs in a pattern reflecting the flanges on the underside of the door. It results in deterioration and efflorescence of the stairs. This is most apparent in the summer, when the sun is on that side of my home. The entry is well-sealed from my basement, so the condensate is not coming from the house. My home has a French drain and sump pump that works well in removing water from the perimeter of my home. How should I address this issue? Can I seal the stairs and walls of the concrete access hatch without causing even more issues/concrete surface deterioration? I don’t think the issue existed until a good door was installed, closing off direct access to the basement from the well. The air used to flow directly into the basement, heating it up in the summer or making the basement very cold in the winter. We can’t return to that situation. Help.

BSMORIN

A. Yes, sealing the concrete will help protect the steps. Bilco recommends the use of an insulated vertical door at the bottom of the stairs for both energy efficiency and added security, which you’ve done. Bilco brand doors are designed to be weather-tight, but are intentionally designed with air gaps on the underside. This is supposed to equalize the temperature on both sides of the metal doors to eliminate condensation.

Bulkhead doors are not airtight. In the summer, warm moist outside air comes in and condenses in the cooler stairwell or basement. As the outdoor metal surface gets hot, the cooler stairwell/basement air generates condensation on the underside.

Foam insulation on the inside of the door probably will help to some extent. You’ve got to find the source of the moisture and eliminate it, or you’ll have other problems. Here are some ideas:

■ Ensure the bulkhead is sealed/caulked well at the house foundation joint

■ Make sure the bottom step is sealed well to the foundation footing

■ Is the door to your basement at the base of the stairs weather-stripped? If so, is the weather-stripping airtight (including at the threshold)?

■ Was spray foam installed between the door jamb and the concrete walls?

■ Has the joint between the pressure-treated mudsill and the top of the concrete wall been sealed with sill-seal caulking or foam sealant?

■ Is the band joist area airtight (with glued rigid or aerosol foam, sprayed icynene, caulk, or some combination of the above)?

■ Are the concrete stairs and exposed foundation wall sealed?

If all of these steps were taken and moisture is still coming into the bulkhead, the only way to eliminate the condensation is to stop the humid air or to provide ventilation to that area. This can be solved by opening the doors (a security issue) or installing vents on the sides of the bulkhead. As for ventilating the bulkhead doors themselves, you could install circular aluminum vents, which come in various sizes. I’m not even sure that it would make much difference, because most Bilco doors are not really airtight, and any moisture should escape fairly easily.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard.