Rebuilding old chimneys -- with a European technique

Steve Vinal is a brickmason by trade who has considerable experience in chimney building and rebuilding. Too many unsafe chimneys in this new age of wood- and coal-burning stoves provided a demand for his services. But the look of dismay that would flood a homeowner's face every time he gave an estimate got to him in the end.

So last year, when he saw an advertisement that offered a less-expensive, yet equally sound solution to the problem of old chimneys, he responded with enthusiasm. Now Mr. Vinal is among a growing number of dealers around the country who renew chimneys structurally by relining them with a poured, high-temperature refractory cement.

If you long for the return of a blazing hearth to your home but question the soundness of your chimney, this relining option might be worth investigating.

In Holland, where the technique was invented more than two decades ago, and in Britain, where it was further developed and refined, the system is known by several names. On this side of the Atlantic it is called PermaFlu.

The name is supposed to represent what the inventors claim the system does: Upgrade on a relatively permanent basis the unlined brick or stone chimneys that predominate in all but the more-recently constructed homes and those modern homes with cracked clay liners.

In simple terms, here is what happens to a chimney that is given the PermaFlu treatment:

The installers come in, clean the chimney, and insert an inflatable form. The form is centered so that there is a minimum one-inch-thick wall of mix all around. This can readily be accomplished even in a serpentine chimney. A slurry of refractory compound is poured around the form. The following day, the form is deflated and removed, leaving a rounded flue that can be 6, 7, 9, or more inches in diameter.

In Britain, the system has been used to line industrial stacks 4 feet in diameter and hundreds of feet high.

The exact composition of the refractory slurry (perfected only after years of trial, according to the manufacturers) is a trade secret. But it does contain certain types of volcanic rock which, while light in weight and incredibly heat-tolerant, also add to the insulating value of the lining.

This has two advantages:

* The flue warms up rapidly, creating a good draft which, in turn, reduces the amount of creosote deposited on the walls.

* In the event of a chimney fire, heat transfer through the chimney to the surrounding wooden floors or walls is dramatically reduced.

In one test, when the PermaFlu stack temperature was raised to 2,100 degrees F., the exterior temperature of the chimney was only 70 degrees F. above the ambient temperature of the room.

Because the slurry must be poured in a highly liquid state, it has the capacity to creep in and fill all cracks within the chimney. This means that the chimney itself is structurally strengthened while being relined.

PermaFlu has been tested by the Arnold Greene Testing Laboratories in Natick, Mass., to meet the Massachusetts code and Underwriter's Laboratory Standard No. 103 for heat resistance, strength, acid absorbancy, and freeze-thaw tolerance. High-temperature tests have exceeded the 2,100 degrees F. mandated in Canada, which is currently in excess of any standard required in the US.

The PermaFlu option is far less expensive than reconstruction.

''But it is not cheap,'' cautions Vinal, who has relined chimneys for as little as $850 up to several thousand dollars, depending on length and the number of twists and turns the chimney takes. A rough ball-park figure is $1,000 for a straight chimney 25 feet in length.

According to a representative of Chimney Relining International, which brought the technology to this country, the poured liner generally is about 30 percent more expensive than a stainless-steel flue surrounded with noncombustible insulation. But stainless steel does not strengthen the chimney in any manner. Moreover, even good-quality stainless steel is not totally immune to acid, which is particularly prevalant in stacks where coal is burned.

No one is yet sure of the exact life expectancy of the poured flue. But chimneys relined this way in England and Scotland more than 16 years ago reportedly still show no signs of deterioration.

Insurance companies, too, are recognizing the value of the system. Not only does the refractory cement withstand higher temperatures than conventional clay lining, but single-unit pouring (compared to clay liners laid one on top of the other) is seen as an advantage.

Recently, a PermaFlu installation was made in a new home under construction in Sugar Hill, N.H., because the contractor felt it was superior to the moderately less-expensive clay liners.

Introduced into the US two years ago, PermaFlu still is not available everywhere, but the number of trained installers is expanding at a rapid clip. For information, write to: Chimney Relining International Inc., PO Box 4035, Manchester, N.H. 03108.