Elastomeric coating has rubberlike properties and expands and contracts with the surface to which it is applied.

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Q: I read your article on elastomeric coatings. Are these the lifetime coatings that some companies advertise, usually at home improvement shows?

A: There is nothing I’ve seen from those who manufacture or apply elastomeric coatings saying that they last a lifetime. What I have seen is that these coatings do last longer than, for example, the asphalt coatings used on the flat roofs that abound in cities including Philadelphia.

A few years back, I wrote about the Energy Coordinating Agency of Philadelphia’s “cool roofs” program, which was designed to help elderly city residents reduce their summer electric bills.

Flat row house roofs were coated with a white elastomeric substance that reflects heat and keeps interiors cool. The coating was manufactured, I believe, by Rohm & Hass (now Dow Chemical), and, at the time, came with a 10-year guarantee, according to the people at the agency.

Elastomeric coating has rubberlike properties that return it to its original dimensions after it is stretched or deformed. The coating expands and contracts with the surface to which it is applied.

Over time, heat, sunlight, and cracking due to expansion and contraction will degrade a roof, Dow says. The traditional model was to tear off the aging roof and replace it after 15 or 20 years.

“Elastomeric coatings could last the lifetime of the building with regular maintenance,” Dow says. Maintenance is limited to occasional cleaning with a hose or power washer and reapplying the coating every 10 or 15 years.

“A mere five-year increase in roof service life should reduce the cost of roofing by 21 percent, cutting landfill waste from roofing,” Dow says. “Roofing waste currently represents almost 4 percent of the total volume of solid wastes in the United States.”

Again, nothing lasts forever, but proper maintenance can extend the life of just about everything — furnaces, central air systems, decks and roofs.

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Reader Karen Cameron sent this along.

“My mother’s kitchen sink started to make a gurgling noise which two different plumbers could not diagnose. They both sent snakes down the sink drain. The second plumber told her that she would have to upgrade her septic tank to solve the problem.

“I told her to go up on the roof, locate the vent to the sink and run water down it. If it did not drain down immediately, there would be a clog. It did not drain, and she called a plumber to replace the old galvanized vent pipe that had filled with rust scale over many decades.

“I just read the advice you gave to a fellow with a Toto toilet who smelled sewer gas in his powder room. It is quite probable that the odor has nothing to do with the toilet or the drain pipes, especially since the fellow said they didn’t seem to be clogged.

“Sewer gas needs to vent properly or it can enter the house as a ‘burp’ though the ‘P’ traps when water drains through the system. This is because the vents, when working properly, allow air to be pulled into the system from above the drain pipes so that a vacuum is not created that pulls water out of the traps.

“Over time, vents can become clogged and not work to regulate the pressure in the system adequately. The vents can be checked and “snaked” from the roof.

“Sewer gas is a dangerous problem that should not be ignored. If it occurs, it is because the traps are allowing gas to enter either because of a siphon effect that prevents venting; dry because of a leak in the trap; or dry for a long period of time.

“I hope you will let your readers know about this common problem.”

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Q: For a property at the seashore with a crawlspace, I’ve installed vapor barriers. For the vents, Internet information is pro and con about vents. Some say keep them sealed; others say keep them opened.

A: I’ve reported on the debate before, and it is split down the middle. I keep mine closed. The previous owners kept them closed. Fifteen or so years since the addition, no problem.

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(Contact Alan J. Heavens: aheavens@phillynews.com)