Artillery fungus difficult to remove, but you can try

Q. My daughter lives in the state of Georgia in a rental apartment attached to a horse barn.

The owner says the combination air-conditioning and heating unit does not need cleaning or regular maintenance. My daughter changes the ceiling filters regularly.

The problem is a terrible odor (dirty socks is her description), but I think it smells like sewer gas. There is a leach field.

This odor was minimal when the A/C was running. When she switched to heat, the odor was terrible. The odor comes from the bathroom only.

The A/C and heat unit sits on the ground outside the bathroom, and it gets rained on. The drainpipe under the bathroom sink had a valve, which we replaced, but the drain was upside down. The odor diminished for a while. When I close the bathroom door, there is no odor.

Do you have any ideas?

A. Air-conditioning condensers are installed outside and are subjected to the weather. That is not the problem. If the furnace is oil-fired, it should be serviced yearly to maintain top performance. If it is fired with propane or natural gas, it should be checked for safety. The furnace filter should be replaced every three months with a MERV (minimum efficiency reporting value) rating of at least 7 to filter mold, spores, dust mite debris, cat and dog dander, etc.

The fact that you have isolated the odor to the bathroom seems to indicate that sewer gases from the septic system are entering the bathroom.

The odor is more prevalent in the heating season because of the temperature differential between the indoors and outdoors. That differential encourages infiltration of outdoor air into the building to equalize the negative pressure created by the exfiltration of warm air through any cracks and crevices in the upper parts of the building.

One of the easiest points of entry is a failed toilet wax seat. Another possibility is a siphon trap under the sink — the trap which you found incorrectly installed. If the waste pipe under a sink has a siphon trap — frequently found in older houses and unusual installations — the water in the trap, which creates a seal to block sewer gases from entering the house, can be siphoned off with a gurgling sound when the sink, filled with water, is drained.

In the summer, when the air conditioning is on, the problem is minimized because the air temperature outside is higher than inside.

A licensed plumber should check these possibilities and correct the problem. Hopefully, this is all it is.

Q. I read all your columns in our newspaper and clip most of them for later use when something comes up. The one I didn't clip was the one about the tiny black spots all over this person's siding, and what they can do about it. You can't even pick them off. Now I find myself in the same mess — tiny black spots on my white vinyl fence.

My daughter parks her new silver car in the driveway, and her car is covered with these tiny black spots. Even her car windows are covered! She thought it was sap from a small tree out front, but I don't think so.

I seem to remember your earlier answer: something to do with mulch and spores. Could you run this again and tell us how to remove these black spots?

A. These tiny black spots are most likely artillery fungus, which comes from the decomposition of certain organic mulch in the spring and fall. It does not occur in the winter or summer because of the cold or hot temperatures. The spores can shoot up to 20 feet or more, hence the name “artillery,” and they are particularly visible on light surfaces.

According to an earlier mention of the Penn State Extension Service, this fungus was considered almost impossible to remove without causing damage to the surfaces. Or so I thought, until a reader mentioned that he was successful in doing so following a new Penn State Extension Service report that several people have had good luck with Mr. Clean's Magic Eraser. The trick is to wet the spots first and wait several minutes for the packets to soften. That seems to make them easier to “erase.” Another Pennsylvania reader wrote that he finds the spots easier to remove after they have frozen solid over the winter. He uses a plastic scraper and has had good luck with it. My concern is whether it will leave some mark on the vinyl siding or the car.

To prevent recurrence, you can add new organic mulch yearly in the spring, remove the organic mulch and replace it with new mulch yearly or use cypress mulch, which seems immune to the formation of artillery fungus. Rubber mulch is another option; it comes in small brown pellets.

Q. We have an 8-by-24-foot, three-season brick enclosed front porch with a heat duct from the furnace.

Two years ago, we replaced all 13 windows with good quality replacement windows. Now, during the winter, frost will form on the brick.

Our furnace is equipped with a humidifier. We were told to add a cold air return on the porch.

Should we attach foam board insulation to the interior brick walls, and what would be the best way of doing this? Would we need a vapor barrier?

A. Frost is forming because you have improved the airtightness of the porch with better windows. This has reduced the exchange of air in the room, which reduced the relative humidity (RH).

You may wish to check the RH in the entire house. If it is above 30 percent, you may want to lower it. This may solve your problem.

However, if it is easy to have a cold air return added, it's an idea worth considering to improve the air circulation in the porch, but it needs to be installed in a way to encourage air circulation throughout the entire room. It should be in an area opposite the warm air register and as low as possible.

You didn't say where the supply register is, but I assume that it may be in the ceiling of a brick structure. The return should not be in the ceiling, as it would draw the warm air along the ceiling right back to the furnace before the room can benefit from it. If it isn't easy or possible to add a return air duct, one way to provide return air is to leave the door open when you are using the porch or cut an inch off the bottom of the door to the house. But that would not work too well in the fourth season, so you have to compromise.

Installing rigid foam insulation will certainly greatly improve your comfort, but it will need to be covered by some protective material according to the building codes I am familiar with, and for aesthetic reasons as well.

If you choose to use extruded polystyrene (XPS) rigid foam insulation (blue, pink, gray or green), it can be fastened to the brick with polyurethane caulking compound or Styrobond as long as the wall surface is basically smooth — i.e., no irregularities that would keep the insulation from being in contact with the entire wall. Some construction adhesives may also be used as long as they are compatible with XPS insulation.

Apply generous, walnut-sized dabs every two feet or so and press the insulation as hard as you can onto the bricks. Gypsum board can be applied to the insulation with the same type of adhesive.

You will need “grounds” (wood strips) around all openings and along the base of the walls and the ceiling to attach trim and moldings.

If you choose polyisocyanurate (known as polyiso for short) rigid insulation with an aluminum skin, it will need to be installed with mechanical fasteners, as the skin is likely to separate from the board if adhesive is used.

An alternative is to fasten furring strips to the bricks 16-inches on center with Tapcon fasteners. Screw the insulation panels and the drywall to the wood strips.

If you prefer to use paneling, you will need to use furring strips. The paneling should be coated with a flame-resistant paint or stain.

All electrical outlets will need to be safely brought forward or extended; a licensed electrician should take care of this step.

You do not need a vapor retarder.

Q. I am writing in regard to a problem we have with our integral garage floor. Our home was probably a prefab home from the 1940s, which we remodeled in the '80s. However, nothing has ever been done to the floor in the two-car garage. It is starting to “crumble” in areas, leaving a gritty mess as we walk into the basement. Do you have any recommendations of what we can do other than replacing the entire garage floor?

A. If there is room to do so (at least 2 inches at the door to the house), a concrete contractor or competent mason can remove all loose material from the existing slab and lay a new vinyl-reinforced concrete cap over it, tapering it at the garage door so as not to affect the door's operation.

Another option is to install a new floor covering. A very popular choice is Race Deck, www.racedeck.com. Another choice is Swisstrax: www.swisstrax.com.

Be sure the covering you choose is appropriate for use where cars are garaged.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. His book, “About the House,” is available at www.upperaccess.com and in bookstores. His website is www.henridemarne.com. Readers can send questions to Henri de Marne's email address at henridemarne@gmavt.net, or to First Aid for the Ailing House, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.

© 2014, United Feature Syndicate Inc.