You Can Blame Moisture for Corroding Thresholds

QUESTION: Looking for a home to buy, we’ve noted a lot of sliding-glass door thresholds that are eaten away, sometimes with gaping holes, sometimes minor, but always unsightly. I guess this is fairly common, but I looked at two side-by-side houses, built at the same time, where one had massive damage to the thresholds and the other only slight. Why? The other part of my question is, what if anything can be done about this, short of having new doors installed?

ANSWER: Aluminum is very corrosive when exposed to alkaline substances. Concrete (and stucco and similar materials) are alkaline, and in the presence of moisture will corrode. The key to the differences you saw between similar houses, and the reason aluminum windows are less affected, is the difference in moisture.

Thresholds are near the ground, which means that a difference in watering habits or grading or even innocent but repeated hosing off the patio has a profound effect on the corrosion that occurs.

A few years ago, builders started addressing this problem by putting a moisture barrier under the thresholds to protect the aluminum. That’s also the clue to repair, which requires only a replacement threshold, not a new door. There are specialists who do just that. Be sure the installer waterproofs the concrete (mastic works fine) before laying the new threshold.

Where to Get Second Opinion on Problem

Q: Our garage slab has a fairly prominent X-shaped crack. A contractor said this was an indication of severe soil problems, and made a case for thousands of dollars in corrective work. Now we’re worried. Who should we call for a second opinion?

A: You might try your local building department first, to learn if they’re willing to come out and review your problem. If not, many home inspectors will do a partial inspection such as this for a nominal fee. Make sure the inspector isn’t selling you anything but his advice, so you’re assured of an impartial opinion. Look in the Yellow Pages under “Building Inspection,” and look for a CREIA/ASHI affiliation as an indicator of their professionalism.

Gas Co. Can Advise on Furnace for Free

Q: Now that the heating season is with us again, I wonder if my yearly routine of relighting the furnace pilot and changing the filter is really enough. I’ve heard some horror stories of carbon monoxide poisoning, and wonder what else I should do.

A: The gas company offers excellent free service that we highly recommend. When relighting your pilot, they will run a safety check on the furnace. If you ask the technician, they will most likely also advise you on possible other maintenance such as oiling the blower, changing the blower belt or plugging air leaks. If repairs are required, you’ll need a heating contractor.

Ross is the public relations chairman for the California Real Estate Inspection Assn. (CREIA / ASHI), a statewide trade association of home inspectors. Readers may send their comments or questions on home inspection topics to Bill Ross, CREIA, 1100 N St., Suite 5-D, Sacramento, Calif. 95814.