Swelling Gasket

Important: Most catalytic woodstoves do NOT require additional gasket material when you install a new combustor. Only use Condar CatGard™ gasket if your stove's original combustor installation included gasket material.

CatGard expanding gasket If you see a gap around the edge of your combustor, that doesn't mean it's necessary to fill it with gasket. Your combustor installation doesn't have to be airtight to achieve optimal operation.

CatGard gasket may be used effectively only if your stove was engineered for its original combustor to incorporate gasket in its installation. To use CatGard improperly risks serious damage to refractory brick in your woodstove, and to your new combustor, which may be broken when the powerful gasket expands.

Note: Professional installers often use gasket when it's not needed. Just because your installer packed in gasket material last time your combustor was replaced, doesn't mean it was installed correctly. Consult your woodstove owner's manual for information about the original combustor installation.

How does it work?

The golden flecks you see in CatGard are mineral mica, which expand rapidly when exposed to exhaust gases and water vapor 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.

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.

Its ability to swell makes CatGard swelling 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 Gaskets

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.

Uncanned Combustors

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.

Canned Combustors

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 in (15.24 cm) Diameter Round Combustors, Canned

Most woodstoves that have round catalytic combustors measuring approximately 6 in (15.24 cm) in diameter, 2 in (5.08 cm) thick, require an outer gasket. Therefore 6 in (15.24 cm) 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.)

Ordering 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 (48.26 cm) of gasket. 7 in (17.78 cm) round combustors require 22 linear inches (55.88 cm) of gasket. Oblong combustors require gasket twice the length, plus twice the width, PLUS 2 inches (5.08 cm) - a half-inch for each corner.

Standard One-Sixteenth in (0.15 cm) Thick Gasket

Most applications need CatGard expanding gasket that comes 1/16 in (0.15 cm) 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 in (2.54 cm) Wide Gasket 2 in (5.08 cm) Wide Gasket
Code 1P430: 40 in (101.6 cm) long Code 1P259: 17 ¾ in (43.18 cm) long
Code 1P100: sold by the inch Code 1P346: 22 in (55.88 cm) long
    Code 1P350: 31 in (78.74 cm) long
2.5 in (6.35 cm) Wide Gasket 3 in (7.62 cm) Wide Gasket
Code 1P403: 32 in (81.28 cm) long Code 1P426: 31 in (78.74 cm) long
    Code 1P426: 31 in (78.74 cm) long
    Code 1P427: 17 ¾ in (43.18 cm) long
Extra-Thick ¼ in (0.635 cm) Gasket
  CatGard gasket is available in extra-thick ¼ in (0.635 cm) -- 2.4 in (6.09 cm) wide and 32 in (81.28 cm) long. The order code is 1P401.:
Order your gasket here (standard or extra-thick).

Technical Notes

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.

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