Cast-in-Place Flue Lining Systems

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Author – Marge Padgitt

Homeowners have asked for information on what types of flue lining systems are available for masonry chimneys and what the advantages or disadvantages are among them. 

As a chimney contractor, we have used all types of lining systems so I’m familiar with each.  In this next series of articles I will give detailed information on each type of system. Chimney flues need to be relined for various reasons. 

During a chimney fire, clay tile flue liners often crack and break and need to be replaced.  In other cases, the flue liner is improperly sized or has multiple missing mortar joints or spalling flue tiles. Some older chimneys may not have a flue liner at all.  In each of these cases, relining is necessary and it becomes the job of the chimney professional to determine which method would be best to use for that particular application. 

In most cases, more than one method would work and it becomes the homeowner’s choice at that point. Cast-in-place flue lining systems are by far the Cadillac of flue liners.  They offer good insulation, excellent durability, and actually strengthen the chimney itself. 

A cast-in-place or ceramic flue liner is installed much differently than other types of liners.  If a clay tile flue liner is installed it is removed from the chimney first.  If there are multiple liners serving different appliances they would all be removed if there are no brick wythe walls between the flues.

Next, a block is installed at the damper area to prevent the liquid mix from entering the fireplace.  Then a heavy duty rubber tube with spring spacers is inserted into the chimney and inflated to the proper size.  The liquid mix is slowly poured around the inflated tube while a vibrator pushes the mix into every nook and cranny and removed air bubbles. 

This is continued until the entire flue is completed, then left to set up for approximately 24 hours.  The next day the crew will return to deflate the tube and remove it, leaving behind a hard, ceramic circular or oval shaped flue.

In most chimneys, the smoke chamber area above the damper and before the flue begins is rough and unparged (coated with insulating mortar). 

One way to address this potential problem is to use the cast-in-place mix in the chamber, let it set up for a short period of time, then carve out a new smoke chamber.  This insulates the chamber and keeps heat inside the area instead of migrating through the masonry chimney.

Cast-in-place lining systems are tested and listed to U.L. 1777 and allow for close clearance or zero clearance applications. This means that if combustibles are installed right next to the chimney, this application will make the chimney much safer because it keeps heat inside the chimney and away from combustible materials.

When searching for a good brand be sure to look for the U.L. listing and for the thickness required for the listing.  Not all cast systems are alike.

Due to the fact that the mix starts out as a thick, heavy liquid it seeps into any holes or cracks in the chimney during the pouring process.  By filling these gaps, the process strengthens the chimney, which is something that other lining systems cannot do.  This is often important to the homeowner who wants to maintain the integrity of their masonry chimney.

As far as price is concerned, the cast-in-place ceramic flue systems are more expensive than other methods, but many homeowners find that the value is worth the cost.

Cast-in-place liner benefits:

  • Improves the structural integrity of the chimney
    Lifetime warranty by the manufacturer
  • Installs around offsets (bends) in the flue
    Suitable for all flues serving wood-burning stoves, fireplaces, and gas appliances
  • Can be used in multiple flue applications
  • Provides a hard, ceramic, smooth surface which assists flue gasses in exiting the chimney


+ the graphic at the top of this article was supplied by

+ the graphic at the top left of the article was supplied by HearthMaster, Inc.

+ the last graphic was supplied by HearthMaster, Inc.

~ Marge Padgitt







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