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Historically, the only available method to repair defective or deteriorated mortar joints between flue liners in a masonry chimney was to reline the flue. Using the FireGuard ceramic sealant, the need to reline the chimney is negated, saving time and expense.

The Problem
During original construction, it is not uncommon for masons to improperly align the flue liners or neglect to fill the joints between the flue liners with the appropriate refractory mortar. As stated in The BOCA National Mechanical Code, M-1207.2.1 Fire-Clay flue liner: “The fire-clay flue liner shall be installed ahead of construction of the chimney as the chimney is carried up and carefully bedded one on the other in an approved medium-duty refractory mortar, with close joints left smooth on the inside.” Even if the mason filled the joint with mortar, it most likely was the same mortar used to lay the brick, block or stone, which is not an approved refractory. In fact, standard mortar has almost no refractory properties. Standard mortar in the joints of flue liners cannot withstand the adverse conditions present within a chimney environment. The result of using standard mortar is rapid deterioration of the joint, ultimately leaving dangerous openings between the flue liners.

The Danger of the Problem
The results of these improper practices are dangerous openings within the flue area. These openings allow flammable creosote (by-products from wood combustion) to build-up between the outside of the flue lining and the inside of the chimney casing. Should these flammable deposits ignite, the heat and quite possibly the flame could transmit to the dwelling. As recommended by the National Fire Protection Agency 211 - Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, “If the flue liner in a chimney has softened, cracked or otherwise deteriorated so that it no longer has the continued ability to contain the products of combustion (i.e., heat, moisture, creosote, and flue gases), it shall be either removed and replaced, repaired, or relined.” In the past, relining was the only option .  Now, you and your chimney professional have a viable, safe alternative - FireGuard ceramic sealant; it is the most cost effective product addressing dangerous gaps between flue.

The Solution
The FireGuard ceramic sealant is a high-duty, refractory mortar specifically designed to correct open mortar joints, thus negating the need to reline the flue. The 3,200 degree service temperature far exceeds the requirements for residential chimneys. Applied by chimney professionals, the unique FireGuard material forms solid, smooth, water and acid resistant joints throughout the entire flue area. Once properly installed, the new FireGuard joints prevent the passage of flammable creosote through the joints, thus preventing the build-up of flammable creosote outside the flue area. In addition, the new FireGuard joints reduce heat transfer through the joints to the interior wall against the dwelling. Under normal operation of a masonry chimney, FireGuard is guaranteed not to loosen or dislodge from the joint(s) for a period of twenty years (please see your chimney professional for details).

Why FireGuard?

The Fireguard process typically costs less than traditional linings.

The FireGuard process is in full compliance with standard building codes. In fact, the FireGuard material far exceeds the service temperature requirements for residential applications.

The majority of the FireGuard process is usually completed within a single day, with much less disturbance to the inside of the home since the flue liners do not require removal.

The FireGuard process does not appreciably decrease the area of the original flue; therefore, the performance of the fireplace or appliance should not change.

FireGuard material exceeds all requirements for refractory mortar material.

The FireGuard material is guaranteed for twenty years not to fail (please see your chimney professional for details).

The FireGuard process was developed by Firesafe Industries, a company special- izing in chimney restoration products and processes for over 45 years.

The FireGuard process is protected under patent laws (patent pending).


N.F.P.A. 211 Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2003 Edition

  • Liners shall be bedded one on the other in a medium-duty, non-water-soluble calcium aluminate refractory cement    mixture, or its equivalent.
  • Joints shall be left smooth on the inside.

Test results indicating FireGuard’s compliance with N.F.P.A. 211,

* A.S.T.M. C24 Pyrometric Cone Equivalent
  PCE Value 33-34         
  Deformation Temperature 3,169 F – 3,205 F

Results indicate super-duty classification, which exceeds medium-duty requirement.

* Resistance to Action of Acids for Nonmetallic Flue-Gas Conduit (Section 28, U.L. 1777)
   - 3.19% pass

* Freezing and Thawing Test for Water-Absorptive Nonmetallic Materials (Section 29, U.L. 1777)
   - 4.78% pass

International Residential CodeĀ® for One-and Two-Family Dwellings, 2003 Edition

R1001.9 Flue lining
Fireclay flue liners shall be laid in medium-duty refractory mortar conforming to ASTM C 199 with tight joints left smooth on the inside….

Test results indicating FireGuard’s compliance with I.R.C code: R1001.9

* A.S.T.M. C24 Pyrometric Cone Equivalent
   PCE Value 33-34         
   Deformation Temperature 3,169 F – 3,205 F

Results indicate super-duty classification, which exceeds (ASTM C 199) medium-duty classification.

* Orton Refractories Testing & Research Center