QUESTION: There is a green stain on the wash basin and also on the tub in my summer home. The water is clear, but it leaves this stain. Would you know what causes this? Are the pipes too old?
ANSWER: The problem is not with the pipes, but with the water. Probably the water is soft and has a high carbon dioxide content, which makes it slightly acidic. This water leaches small amounts of copper from the pipes. The stains are left from water that drips from a faucet. Each droplet evaporates, but it leaves a copper residue, and when the residue reacts with the air, it turns green.
Remove the stains with a weak acid on a sponge. Try using lemon juice or vinegar. The stains can also be removed by gentle cleaning with a mild scouring cleanser.
The green staining problem can be eliminated with a water treatment system.
Device Indicates When to Change Air Filter
Q: The instructions on our air conditioner-heat pump called for a filter change once a month. We have done this every month, and now with the advent of the heating season and the use of our wood fire, the filter seems dirtier than previously. Is there a method or instrument that can help us determine when it's time to change the filter?
A: Yes, there is such a device. Honeywell Inc. has an instrument called a filter flag indicator, model No. S830A. The device costs about $48, and it will do just what you want and maybe a little more.
The unit is contained in a small molded plastic case and can be mounted either directly on the blower compartment or remotely mounted. When the air filter (disposable washable or electronic) becomes clogged, it affects the suction pressure within the blower compartment. When the suction is greater than the set point of the device, it releases a red flag marked "Change Filter."
Accessories are available through your Honeywell dealer that enable you to wire the device so a light flashes on your thermostat. The light is part of a sub-base that mounts on the wall thermostat.
There Are Ways to Rid Floor of Oil, Grease
Q: What's the best way to clean oil and grease from a concrete floor?
A: If oil has been freshly spilled onto a concrete surface, blot up as much as you can, then cover the spot with one of the following: powdered calcium carbonate, hydrated lime, talc or fuller's earth. Portland cement can also be used. Let powder stand for 24 hours, then scrape it off.
If oil has penetrated into the concrete, scrape off whatever remains on the surface with a putty knife and then cover the stain with a stiff poultice made from one of the powdered substances above combined with a solution of one part trisodium phosphate and six parts water. Let the poultice stand 24 hours, then scrape it off. Scrub the surface with clean water.
Grease is easier to remove than oil. If scraping and scrubbing don't work, use a poultice made from benzene, naphtha or trichloroethane and an inert powder. Allow it to stand 24 hours, then scrape the surface clean.
To submit a question, write to Popular Mechanics, Reader Service Bureau, 224 W. 57th St., New York, NY 10019. The most interesting questions will be answered in a future column.