Masonry Magazine December 2012 Page. 21
Refractory Mortar
While our building codes may have been a bit confusing or inconsistent in previous decades, that is no longer the case. The International Code Council (ICC), the International Residential Code (IRC) and the National Fire Protection Association (NFPA-211) now all require refractory mortar tested to American Society for Testing Materials, ASTM C-199, medium duty. Also called out in these codes are the high-temperature resistant manufacturing standards for firebrick (ASTM C-27 & C-1261) and for clay flue lining (ASTM C-315). It does make sense that the mortars used for installation of firebrick and clay flues should be manufactured to a high-temperature resistant standard as well. After all, what part of residential construction should have more attention to fire safety than that part in which we are going to intentionally build a fire?
There are basically two kinds of refractory mortar conforming to ASTMC-199 and permitted by code. Non-water soluble refractory mortar (sometimes called hydraulic setting) is a dry blend, requiring only cold water to be added, usually ships in a bag, and sets up or cures much like a regular mortar mix. The second type is a premixed version. It comes in a pail and is about the consistency of drywall compound. It usually requires no additives, and with a little mixing is ready to use.
Non-water soluble refractory mortar
THIS TYPE OF REFRACTORY MORTAR is a blend of aggregates and binders that are not only high-temperature
Questions Answered
Q: How long does the installation need to set after completion before building a fire?
Bob: One overnight of drying is sufficient for any installation.
Q: Where else do you use refractory mortar on your Rumford installations?
Jim: I use refractory mortar for setting the firebrick and the throat and then for installing the smoke chamber as well as all of the clay flue lining.
Q: Where can people find all they need to know about a masonry fireplace, chimney, or bread oven?
Jim: Try rumford.com.
Q: Any new publications regarding masonry fireplace or chimney construction?
Bob: New York State Concrete Masonry Association, Tech Spec 3.5, online at www.nyscma.org.
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READER SERVICE #173
December 2012
MASONRY 19