Corbelled smoke chamber repair for Catalina homes

Refractory mortar and ASTM C199

ASTM C199 is the test method the code names for refractory mortars, the heat-rated mortars used inside fireboxes and smoke chambers. The code calls for parging made from mortar that conforms to it, and for firebrick linings laid in medium duty refractory mortar.

In practice, that means the product in a bucket on our job has been made and rated for fireplace heat. Ordinary masonry mortar is made for walls and weather. We name the refractory product we plan to use in the written estimate, so there is no question about what goes on your chamber walls.

How deposits build up on rough walls

Smoke cools as it rises through the chamber, and some of what it carries condenses on the walls. On a rough or stepped surface, those deposits have ledges and pockets to collect in, and each fire adds a little more.

A heavy layer changes the chamber shape and hides the masonry underneath. It also has to come off before any repair. Parging leaves a surface that is easier to brush clean at future sweeps, which is one of the practical reasons homeowners choose it.

Yearly inspection of a parged chamber

NFPA 211 expects every chimney, fireplace and vent to be inspected yearly at the least. A parged chamber belongs in that yearly look like every other part of the fireplace.

At each visit, we check the coat for cracks that have opened, areas that sound hollow and any buildup that has returned. We also check the shelf and damper seat. Most years the answer is a routine note, and the written record helps spot any change early.

• Coat surface and edges
• Smoke shelf and damper seat
• Buildup since the last visit

Flue and liner work kept separate

A chamber inspection often reveals something about the flue above it, such as cracked tiles, open joints or deposits. Those findings belong in the report, but flue repair and liner installation are separate services.

We describe what we saw in the flue, explain whether it needs attention soon or can be watched, and give it its own line when a repair is needed. Chamber work can go ahead on its own when the flue is sound enough to use.

Refractory mortar and ordinary mortar

Masonry mortar for exterior walls and chimney joints is made to handle weather, and it is the right product there. Inside a smoke chamber, the exposure is heat, and the code calls for refractory mortar instead.

Mixing the two up leads to failures, such as ordinary mortar used to patch a chamber that crumbles after a season of fires. We use each where it belongs and name both in the estimate when a job involves inside and outside masonry.