A special kind of gasket is used in the manufacture and installation of woodstove combustors to prevent smoke from leaking around the combustor honeycomb. The expanding gasket made for this application assures that smoke will pass through the cells of the ceramic. It isn't the same kind of gasket used for woodstove doors or elsewhere in wood stoves.
CatGard is the trademark for Condar Company's expanding gasket for woodstove combustors. The golden flecks you see in CatGard are mineral mica, which expand when heated in a hot woodstove, causing the gasket to swell. Once installed in the stove and heated, CatGard can expand permanently to twice its original thickness.
Its ability to swell makes CatGard expanding gasket easy to use by professional woodstove installers, chimney sweeps, and homeowners who perform their own gasket inspections and replacement installations. Regular stove-door gasket material should NOT be used for seating combustors in your stove.
Installing New Combustor Gasket
Once old expanding gasket has been subjected to constant high heat, it becomes fragile when handled. While serviceable in place, it may crumble when you remove your combustor for inspection or cleaning. Go ahead and remove crumbly gasket when new gasket is installed. If any old gasket is stable and serviceable in appearance, it's fine to continue using it indefinitely.
Remember that new CatGard gasket can swell up to a maximum of double its thickness! When your stove is cold and you're installing your new combustor, it's okay if the new gasket material doesn't completely fill the cavity, leaving a thin crack.
The combustor should, however, fit snugly.
Combustors that have no stainless steel "can" must always be installed with new expanding gasket. Uncanned Condar® brand combustors are manufactured wrapped with CatGard expanding gasket at no extra charge. The factory ships the correct gasket already in place, with masking tape to hold CatGard in the proper position during installation.
It isn't necessary to remove the masking tape; the tape will safely burn off the first time the catalyst is activated by heat. Remove the tape, and portions of the gasket, only if your new combustor won't fit in the woodstove with them in place.
Original equipment catalytic combustors that are "canned" (the ceramic is wrapped with a stainless steel strip) should be replaced by new combustors that are also canned. Observe that canned combustors have gasket material sandwiched between the can and the ceramic honeycomb.
Woodstoves with canned combustors may, or may not, require additional gasket outside the can for a good fit inside the stove. This depends on the particular stove design. In some cases the combustor assembly consists of two or more pieces. Gasket should be used between the individual pieces for a good fit.
If your woodstove presently has its original combustor, or a previous replacement combustor installed by a chimney sweep or hearth-shop installation professional, the presence of additional gasket wrapped around the outside of the can indicates you should order an outer gasket with your canned combustor.
Six-Inch-Diameter Round Combustors, Canned
Most woodstoves that have round catalytic combustors measuring approximately six inches in diameter, two inches thick, require an outer gasket. Therefore 6-inch round, canned Condar brand combustors come with additional outer gasket wrap at no extra charge. (If your stove doesn't need the gasket -- if the new round combustor fits tightly without the need for gasket -- don't force it into position. Simply remove the unneeded gasket.)
Condar Company offers CatGard gasket material in several configurations. CatGard is easy to cut with a sharp knife. It may be necessary in some woodstoves to double-wrap the unit to obtain a good seal.
When removing the catalytic combustor from your woodstove for summer inspection, you'll typically see the expanded gasket has become fragile. It may crumble. During the life of your combustor, you'll likely need at least one replacement gasket, and possibly a new one every year -- depending on the design of your stove and your operating patterns. Therefore, since CatGard is inexpensive, it's a good idea to go ahead and get at least one set of replacement gasket when you buy a new combustor, whether canned or uncanned.
To determine which gasket will work best, calculate the outer dimension of your combustor. Six-inch-round combustors require 19 linear inches of gasket. Seven-inch-round combustors require 22 linear inches of gasket. Oblong combustors require gasket twice the length, plus twice the width, PLUS two inches (a half-inch for each corner).
Standard One-Sixteenth-Inch Thick Gasket
Most applications need CatGard expanding gasket that comes 1/16th inch thick. Here are the order codes for this material, arranged by linear inches. More than one piece of gasket material may be needed to wrap all the way around your combustor.
It's okay to have your gasket a little less wide than the thickness of the combustor, but it shouldn't be installed WIDER than the thickness of your combustor.
1 INCH WIDE GASKET
Code 1P430: 40 inches long
Code 1P100: sold by the inch
2 INCH WIDE GASKET
Code 1P259: 17 ¾ inches long
Code 1P346: 22 inches long
Code 1P350: 31 inches long
2.5 INCH WIDE GASKET
Code 1P403: 32 inches long
3 INCH WIDE GASKET
Code 1P426: 17 ¾ inches long
Code 1P427: 31 inches long
Extra-Thick Quarter-Inch Gasket
CatGard gasket is available in extra-thick quarter-inch material -- 2.4 inches wide and 32 inches long. The order code is 1P401.
Order your gasket here (standard or extra-thick).
If the combustor is very loose, even allowing for swelling of the material, it is okay to double-wrap with more than one expanding gasket.
Certain Interam™ brand gasket materials may be substituted for CatGard gasket, but not all Interam gasket is designed for wood stoves.
All CatGard gasket is engineered for woodstove combustor installation purposes. Do not use CatGard gasket for any other purpose. CatGard is sold with no warranty of duration in use, because its serviceability depends upon appropriate installation and operation of individual woodstoves.
Certain publications and manuals list CatGuard, Catguard, or Catgard as Condar's brand of expanding gasket material. CatGard is a trademark of Condar Company, Columbus, North Carolina, USA.